University of Nigeria

Research Publications

OMAR, Suleiman A

utho

r

PG/M.ENG/89/8241

Title

An Appraisal of the Maintenance of Civil Engineering Infrastructure in the Nigerian

Ports

/Fac

ulty

Engineering

Dep

artm

ent

Civil Engineering

Dat

e

December, 1991

Sign

atur

e

AN APPRAISAL OF THE MAINTENANCE OF C I V I L ENGI NEERING INFRASTRUCTURE I N THE

NIGERIAN PORTS

A THESIS PRESENTED TO THE DEPARTMENT OF C I V I L ENGINEERING,

UNIVERSITY OF NIGERIA NSUKKA, I N PARTIAL FULFILMENT FOR THE

AWARD OF THE MASTERS OF ENGINEERING DEGREE I N MATERIALS AND

. CONSTRUCTION.

ENGR. PROF. 0.3 .' EZE-UZOMAKA

DECEMBER 1991.

CERTIFICATION m

OMAR SULEIMAN, A post graduate student i n the department

o f C i v i l Engineering w i t h reg i s t ra t i on No. PG/M.ENG/89/8241,

has s a t i s f ac to r i l y completed the requi rement f o r the degree

o f Masters: Engineering i n C i v i l Engineering.

The work embodied i n t h i s thesis repor t i s o r i g i na l and has

not been submitted i n Part o r f u l l f o r any other diploma o r

degree f o r t h i s o r any other University.

ENGR. PROF: 0.3. EZE-UZOMAKA F SUPERVISOR

DEDICATION g.

" Dedicated t o my Mother AISHATU SULEIMAN.

ACKNOWLEDGEMENT

My greatest appreciat ion i s t o my Supervisor Engr. Prof. O.J.

EZE-UZOMAKA f o r

guidance.

. I thank my w i fe

thank my f r i end

h is advices, understanding, patience and good

Maryam f o r her kindness and encouragement. I also

A lha j i M. Bashir f o r a l l h i s assistance. I also

thank Mallam Anas Suleiman for h is care and understanding.

AN APPRAISAL OF THE MAINTENANCE OF CIVIL ENGINEERING INFRASTRUCTURES I N THE NIGERIAN PORTS

BY *

OMAR SULEIMAN PG/M. ENG/89/8241

- PREFACE

Most o f the problems o f p o r t maintenance i n N i g e r i a a re

associated w i t h t h e h i s t o r i c a l development o f the Por ts . Thus a

h i s t o r i c a l survey o f p o r t development and e f f e c t s on p o r t maintenance

are f i r s t discussed.

Q

Th is i s fo l lowed by a d e t a i l e d assesment o f the causes,

and modes o f f a i l u r e and

The e x i s t i n g methods and

Consider ing the r a p i

t he l a t e s t techniques o f

d e t e r i o r a t i o n i n t h e N ige r i an Por ts .

techn ics o f r e p a i r s a re a l s o presented.

d changes i n P o r t Maintenance techniques ..-.

r e p a i r and maintenance which a r e p e r t i n e n t

t o t he N ige r i an s i t u a t i o n a r e discussed t o p rov ide a gu ide - l i ne

f o r the S t a f f and Management o f the N ige r i an Po,rts.

P

An e f f e c t i v e maintenance programme i s presented i n t he second

p a r t o f t h i s thes is , r e g u l a r i nspec t i on be ing one o f the most

impor tan t c o s t sav ing fea tu res i n maintenance management i s

discussed and appropr ia te recommendations made. , -

A d e t a i l e d survey o f t he techniques and equipments necessary f o r

good ' i nspec t i on o f C i v i 1 Engineering i n f r a s t r u c t u r e a re a l s o presented.

e

F i n a l l y a s t r u c t u r e o f Maintenance o rgan i sa t i on i s proposed and a

d e t a i l e d d e s c r i p t i o n o f the d u t i e s o f each s t a f f . Hierachy o f s t a f f

and the mode o f work o rder execut ion and feedback f o r f u t u r e needs.

a re a l l presented i n d e t a i l . The advantage of proper t r a i n i n g scheme

f o r t he Maintenance S t a f f , w i t h the f a s t changing technology i s

a1 so d l scussed.

F i g 3:2:1

F i g 3:2:2 "

F i g 3:2:3

F i g 3:3:1

F i g 3:3:2

F i g 3:3:3

F i g 3:3:4

F i g 3:3:5

F i g 3:3:6

F i g 3:3:7

F i g 3:3:8

F i g 3:3:9

F i g 3:3:10

F i g 3:3:11

F i g 3:3:12

F i g 3:%3:13

F i g 3:3:14

F i g 3:3:15

F i g 3:3:16

F i g 3:3:17

F i g 3:3:18

F i g 3:3:19

LIST OF FIGURES

Crossect ion of mound as b u i l t i n 1907

East mole a f t e r rehab i 1 i t a t i o n 1991

Breakwater P r o p e r t i e s

lockw wall Re ta in i ng w a l l

Anchored b u l khead w a l l

T h i r d Wharf Extens ion (open c o n s t u r c t i o n )

Typ i ca l O i l Tanker J e t t y

Resu l t f rom acce le ra ted c o r r o s i o n t e s t

E f f e c t o f cover on su r f ace c rack w i d t h

Simple c o r r o s i o n model

Simple v o l t a i c c e l l

C r i t i c a l humid i t y : In f luence o f . humi

atmospheric p o l l u t i o n on t h e r u s t i n g

s t e e l

Mechanism o f P i t t i n g

Typ ica l c o r r o s i o n r a t e o f s t e e l

S tee l Clamps

Patch r e p a i r o f sheet p i l e

\

d i t y and

o f muld

T i e back bulkhead r e p a i r . l i g h t w e i g h t b a c k f i l l

C e l l u l a r sheet p i l e r e p a i r

S tee l sheet p i l e bulkhead replacement

Cathodic p r o t e c t i o n

Cathodic p r o t e c t i o n t o a j e t t y by ga l van i c process 91

Cathodic p r o t e c t i o n t o j e t t y us i ng power

impressed method 93

23. F i g 3:4:1

24'. F i g 3:4:2

25. F i g 3:4:3

26. F i g 3:4:4

27. F i g 3:4:5

28. F i g 3:4:6

29. F i g 3:4:7

30. F i g 3:4:8

31. F i g 3:4:9

. 32. F i g 3:4:10

33. F i g 4:l

34. F i g 4:2

. 35. F i g 4:3

Grab o r c lamshel l dredger

Backhoe dredger

Dipper dredger

Bucket ladder dredger

P l a i n suc t i on dredger

Dustpan Dredger

Water i n j e c t i o n dredger

Cut te r head dredger

Bucket wheel dredger

T r a i l i n g hopper dredger

Factors invo lved i n maintenance

Organisat ion c h a r t

Economic/Financial Analys is f l o w c h a r t

LIST OF PLATES

1. Plate 3:2:1 West Mole showing damaged end

2, Plate 3:2:2 Recently rehabi 1 i tated eas t mole 2 6

3. p l a t e 3:2:3 East mole harbour side 27

4. Plate 3:2:4 East mole sea s ide - 5. Plate 3:3:4 Damaged j e t ty a t Apapa Dockyard

6. Plate 3:3:5 Collapsed quay deck a t Tincan Island Port 67

7. Plate 3:3:6 Do1 phi n damaged by corrosion 7 0

Plate 3:3:7

Plate 3:3:8

Plate 3:3;9

Plate 3:5:1

Plate 3:5:2

Plate 3:5:3

Plate 3:6:1

Plate 3:6:2

Abandoned j e t ty due to corrosion damaged

Cover cleaning of Reinforcement

Cover cleaning for repair of corroded s teel

Warehouse railway system Apapa

Railway i n an undeveloped part of Apapa Port

Maintenance of r a i l in progress a t Apapa quays

Damaged Warehouse a t Tincan Island Port

Settlement a t container Terminal I jora.

LIST OF TABLES

3: 1 Effect of concrete covers on bursting pressure *

3:2 Electro"chernica1 series . 1

CONTENTS ' PAGE

3.2.1 Desc r ip t i on and f u n c t i o n

3.2.2 C h a r a c t e r i s t i c fea tures

1. " INTRODUCTION

2. H I S T O R ~ O F PORT DEVELOPMENT IN NIGERIA

3. DESCRIPTION OF CIVIL ENGINEERING FACILI-TIES AT THE 15

NIGERIAN PORTS. 15

3.1 General 15

3.2 Breakwaters 15

Sources and causes o f damage

Repair and maintenance o f breakwater

Docks .I

Desc r ip t i on and f u n c t i o n

Charac te r i s t i cs o f Docks

Sources and causes o f damage

Repair and maintenance of docks

Dredgi ng

General

Types o f dredgers

Bottom mate r ia l

3.4.4 Disposal o f dredged m a t e r i a l s 107

3.4.5 Operat ion and maintenance 108

3.5 en Port voads and railways

3.5.1 Port raods -

: '3.5.1A Failure of port roads

3.5.18 . Port road maintenance

3.5.2 Port railways

3.5.2A Failure of port railways

3.5.20 Maintenance of port railways

3.6 Transit shed. warehouse and container depots

3.6.1 General

3.6.. 2 Transi t shed

3.6 .a Warehouses

3.6.8 Contai ner depots

MAINTENANCE MANAGEMENT 4

4.1 General 5

4.2 Inspection as an aspect of port maintenance

4.3 Maintenance management pol icy

CHAPTER ONE

INTRODUCTION

~ r o ; the beginning o f c i v i l i z a t i o n and the e v o l u t i o n o f es tab l i shed

communities, t he re has been a need t o t r a n s p o r t people, equipment,

mater ia ls , and commodities by water. Th is r e s u l t e d i n the

establ ishment o f por ts .

By d i f i n a t i o n a p o r t i s a she l t e red area a long a water course

where marine te rmina l f a c i l i t i e s such as p i e r s and wharves a r e

prov ided t o enable sh ips b e r t h fop load ing and o f f l o a d i n g o f Cargos.

T r a n s i t shed and warehouses a re p rov ided where Cargos cou ld be

moved by r a i l road, highway o r i n l a n d waterway connect ion. The

area of in f luence o f the p o r t reaches o u t f o r a considerable d is tance

beyond the harbour.

For e f f e c t i v e opera t ion o f a por t , these f a c i l i t i e s must be kept

i n good working cond i t i on . This necess i ta tes r e g u l a r a t t e n t i o n .

o r maintenance t o r e p a i r o r rep lace damaged par ts , c lean up . accumulated wastes, a d j u s t d isp laced members, t i g h t e n loose p a r t s

e tc .

N ige r i an Por ts development were a1 1 c a r r i e d o u t i n haste. There

was n o t enough t ime t o c a r r y o u t proper s tudy o f t he environment

and prepare adequate design. The aspect o f maintenance which is,

supposed t o have been considered a t t h e design stage was neglected.

F i f t e e n years back our Por ts were mainta ined by e x p a t r i a t e s and

Niger ians.

o f management i s u s u a l l y gained when t h e r e , i s an u l t i m a t e c o l lapse

o r damage. Then they a r r i v e the re w i t h a l l s o r t s o f port-morten

remedies.

Fo l low ing the i n d i g e n i z a t i o n and reduc t i on o f expa t r i a tes quotas,

sthe e x p a t r i a t e s s low ly l e f t and most operat ions were handed over t o

n a t i o ~ a l s t a f f who i n many cases had inadequate t r a i n i n g and experience

t o e f f e c t i v e l y manage and c o n t r o l t h e i r task.

Maintenance was made more d i f f i c u l t by l a c k o f proper equipment t o .

c a r r y o u t s p e c i f i c task. The procurement o f maintenance equipment .

a re n o t g iven proper a t t a n t i o n . The maintenance budget i s always

g ross l y inadequate. The a t t i t u d e o f management t o maintenance i s t he . >

g rea tes t problem fac ing the maintenance management. The management

.' t r e a t s maintenance budget, i f any as an cont ingency budget t h a t c o u l d

be e a s i l y tempered w i t h and d i v e r t e d t o othe; means. The a t t e n t i o n

The 1 ukewarm a t t i tude o f management t o t he maintenance o f i n f r a s t r u c t u r e

was t h e reason f o r t h i s p a r t i c u l a r t op i c . A Survey a long N ige r i an

Por ts w i l l Convince anybody o f t he l a c k o f maintenance of these

s t ruc tu res . Th is t h e s i s i s t o educate t h e s t a f f , Management, o f

t h e N iger ian P o r t i n terms o f technology, equipments and t h e maintenance

management. Th is knowledge i f app l i ed should r e s u l t i n an e f f e c t i v e

maintenance o f these i n f r a s t r u c t u r e s .

The problem of Port infrastructure maintenance is an engineering

and economic problem. The solution of the problem is made much

more difficult than it really should be because the engineers

responsible for the concept, design and construction were often

more concerned with achieving a timely and low cost products rather I

than with consideration of the difficulties,efforts and cost that

would be associated with the necessary maintenance.

Port maintenance is very expensive. Many ports spend more money

on maintenance than on capital investment. The overall maintenance

problem has to be tackled and solved in a we1 1 conceived manner,

using the best available management and engineering concept.

The age of new port construction in the Nigerian Ports which lasted

from 1970 to 1980 is now over. The emphasis now i's on the rehabil i -

tation of existing structures and their maintenance for continuity

of life for uncertain duration. The aspect of maintenance in this

thesis covers both physical facilities and the human resources. . . .

The objective of this study is to achieve an inproved maintenance

of the Nigerian Ports Authority's Civil Engineering.infrastructureS. . , .

This will ensure that Ports infrastructures are kept in good working

condition, with resultant reduced damage to equi pments and cost

effectiveness. This objective will be achieved by applying the

proper technology and a good maintenance management po1,icy. The

technology and the maintenance management pol icy are discussed in

the body of this thesis.

The scope of this study are the Nigerian Ports. As the author is,

an employee of the Nigerian Ports, Authority, access to the ports

facilities and datas was not difficult. The study involved a proper

literature review of the technology and the maintenance management .. .

of Civi 1 Engineering infrastructures in the ports. The ports document

on technology and maintenance were also studied, and finally visits to

the individual ports was undertaken.

There are four factors which the author considers as an indespensable' , ,

part of good port maintenance. These factor are fully elaborated in

the body of this thesis. The highlight of these factors will be briefly

introduced here.

The factors are:

(1) The machanics of deterioration.

The present type of maintenance employed by the Nigerian Ports ,.

Authority does not give time for the proper study of the machanics

of deterioration or failure. As discussed in this thesis most,

if not a1 1 the maintenance carried out are adhoc types of

maintenance. Usually after an immense fai lure or unusable state . .

has been reached. For these reasons at the end of 'a study of

a particular i nfrastructural element, the author has presented ..

the machanics of failure and deterioration. Understanding the

.. - mechanics of deterioration will anable the authority to select

the best and cost effective maintenance to be applied. The

materials, equipment and the technology required for the maintenance

are fully discussed in relation to the Nigerian Ports situation.

..

( 2 ) S t r u c t u r a l Pol i c y .

A good s t r u c t u r a l p o l i c y i s an indespensable p a r t o f good

1;;ai ntenance management. The author has proposed a s t r u c t u r a l - .. ., .. .. , .

p o l i c y f o r t he maintenance. A complete sec t i on o f maintenance

management has been presented. The s t r a t i , f i c a t i o n i s p rope r l y . ,

def ined, each o f f i c e w i t h i t s func t ions . There i s a l so an

attempt by the author t o reduce the bureaucracy associated

w i t h government o f f i c e s ; as bureaucracy causes delay i n j o b

execut ions and gives r i s e t o r e p e a t i t i o n .

( 3 ) F inanc ia l Resources. . .

It i s known f a c t t h a t t he s imp les t process of maintenance cannot

,be achieved w i thou t . fund. The b igges t bo t t leneck i.n maintenance ...

management i s 1 ack o f f i n a n c i a l resources. N iger ian Ports

A u t h o r i t y i s a money generat ing i n s t i t u t i o n , . t he re fo re proper

f i n a n c i a l backing should be g iven t o the maintenance pol i p y . .

f o r the p o l i c y t o be e f f e c t i v e .

. ( 4 ) The importance o f up t o date technology i n terms o f ma te r i a l s ,

equipment and knowledge cannot be over. emphasised. ,,Due t o the I..... . . ,'

g rea t importance of technology the author has discussed and

presented these technologies t h a t cou ld be useful t o the N iger ian

Ports. Some o f the th ings suggested by the author, . include .

t he purchase of these equipments t h a t cou ld f a c i l i t a t e both

p lanning and execut ion of maintenance of s t ruc tures .

Human resources i s the most important element o f maintenance

programme. Up t o date t r a i n i n g o f s t a f f i n t h i s era o f f a s t changing

technolbgy i s very important. Therefore the author has suggested an

up t o date t r a i n i n g f o r a l l cadres o f the maintenance s t a f f .

CHAPTER TWO

2. HISTORY OF PORTS DEVELOPMENT IN NIGERIA

I n t h i s Chapter we i n tend t o l ook i n t o the devel opment o f Por ts

i~ Nige r ia and r e l a t e i t t o the maintenance needs. The design ,, ,. .

I

modes and m a t e r i a l s a re a l so discussed.

The f i r s t p r a c t i c a l approach t o P o r t development i n N i g e r i a

s t a r t e d w i t h the cons t ruc t i on of the East mole breakwater a t

Lagos i n 1907. I n 1908 the cons t ruc t i on o f the S i s t e r mole . .

. .

(West mole) a l so commenced. The cons t ruc t i on o f the West mole '

s t a r t e d s imul taneously w i t h the cons t ruc t i on o f t he custom j e t t y

i n Lagos Is land. (6 ) .

I n 1913 t h e a u t h o r i t i e s decided t h a t t he te rmina l should be

re1 ocated a t Apapa. This was due t o the f a c t t ha t . there was very

l i t t l e room f o r expansion a t the Lagos end. A scheme fo r t h e -

development o f Apapa s i t e was prepared i n 1918 and i n June 1921

a c o n t r a c t was awarded f o r t he cons t ruc t i on o f the f i r s t four

deep water ber ths t o t a l 1 i n g 548.64 metres o f wharfage. The I .

new be r th was designed f o r an u l t i m a t e depth of 9.75 metres

alongside. (6) .

The design adapted was a g r a v i t y wa l l of concrete b locks s e t i n

slopjcy bound. During the cons t ruc t i on of the f i r s t f o u r ber ths

a t Apapa, the volume of imports and exports increased tremendously,

and i n 1929 the re was a c a l l f o r t he cons t ruc t i on of t he nex t

insta lment . However the depressed s t a t e of t he wor ld economy

i n the fo l l ow ing years c u r t a i l e d any plans t o proceed w i t h such

a major p r o j e c t a t t h a t t ime. ..

A t o t a l of 0.53 million tonnes of Cargo had been handled in the Port

in 1929, but in the f i ve years t ha t followed, the f igure f e l l below

0.53 million tonnes, and i t was not un t i l the year of the second

world war t ha t a steady increase was again recorded.

i n 1945 the f igure had reached an annual t o t a l of 769, 150 tonnes and

allowing for special conditions during the war. I t was ant ic ipated

; , t ha t by 1960 t h i s f igure would have reached. 1.52 million tonnes. Based

on t h i s f igure designs fo r an extension t o provide fu r ther 762 metres

of berthage were put in hand in 1948. These berths were constructed

down steam as a continuation of the f i r s t four berths and about 41

hectares of reclamation behind the wharves was undertaken t o accommo-

date t rans i t sheds , warehouses and mars ha1 1 i ng yards.

Prior t o ,1952, the landing of Cargo a t the quays i n Lagos had been

the responsi bi 1 i t y of the Nigerian Rai lway Corporation, with the

marine department being responsible fo r the maintenance of the harbour

channels and berthing of vessels. Within the marine department there

was a port engineer seconded from the Public Works Department,

responsible fo r the maintenance of the quays up t o cope level .

' In 1952 the government appointed a committee t o study the ex i s t ing

system of pore operation in the country and i t recommended a su i tab le . .

organi sa t ion charged with the responsi bi 1 i t y fo r a1 1 ports matters

in the country.

The government examined the report and i t s findings and thereaf te r

promulgated the Port Act 1954 (Cap 115) which resulted in the s e t t i ng

up of the 'Nigerian Ports Authority' as an autonomous public ,

corporation. The Nigerian Ports Authority commenced f u l l operation

on 1 s t Apri 1 , 1955. ( 6 ) .

The 'Authority ' planned and executed i t s f i r s t wharf extent i on

project between 1956 and 1961 f o r the Ports of Lagos and PortHarcourt,

During t h i s period s i x berth with t o t a l quay of 943 metres and four

berths with a t o t a l quay lenght of 506 metres were completed in

Lagos and PortHarcourt respectively . In . addi t i on t o these berths, -

the Nigerian Ports Authori ty completed the construction of new

warehouses in Lagos and PortHarcourt.

The 'Author i t ies ' development programmes between 1962 to 1968 were

based on the guidelines as indicated in the f i r s t National Development

pian 1962 - 1968, which i n i t s e l f was par t of the au tho r i t i e s long

range ten year development programme. The e a r l i e r pa r t of t h i s ' ,

plan period was u t i l i z ed i n completing preliminary studi-es' leading

to the execution of the second extension of Apapa Quays. About 80% 9 .

of the construction work on the four berths, each 152 metres i n

length, four t r a n s i t sheds and two warehouses a t Apapa Port, was

completed, before the Army took over in 1966. The remaining 20%

construction work as well as construction of the open berth, 220

metres in length, a t Apapa quays was completed shor t ly a f t e r the

Army had taken over.

I n Por tHarcour t and a d d i t i o n a l b e r t h 137 metres i n l e n g t h was

constructed du r ing the per iod. During the p e r i o d under, rev iew a

sum o f W45 m i l l i o n was spent on var ious p o r t development p ro jec ts .

Dur ing the pe r iod o f c i v i l war 1967/1970, a l l N iger ian Ports , except

Lagos Port , were c losed t o f o r e i g n t r a f f i c . This r e s u l t e d i n

tremendous f l o w and concent ra t ion o f good i n Lsgos Por t . The p o r t .

o f Lagos was made t o handle Cargo much beyond the designed capac i t y

and t h i s c rea ted the f i r s t congest ion i n N iger ian Ports. The Federal

Government had t o enact a spec ia l decree empowering the A u t h o r i t y

t o take over a l l the Ports which were p r i v a t e l y owned. 4 s a r e s u l t ,

the Por t A u t h o r i t y acqui red the p o r t o f W'arri f r om ~ o l t rans sport

a t a cos t o f W1.62 m i l l i o n , Burutu P o r t from U.A.C.'of N i g e r i a L i m i t e d

a t W1.2 m i l l i o n and Calabar P o r t f i v e operators a t an est imated c o s t

o f W 0 . 6 3 m i l l i o n . U n f o r t u n a t e l y t h e f a c i l i t i e s w e r e ' f ~ n d i n a -

s t a t e o f decay due t o i n s u f f i c i e n t maintenance and u t te ' r l ack o f - .

development i n terms o f c a p i t a l investment b y , t h e previous p r i v a t e owners. :

The second development p lan 1970 t o 1974 i s a l so a f o u r year pos t war

economic recons t ruc t i on rehab i 1 i t a t i o n and development programme.

: This i s the f i r s t pos t war comprehensive and concerted e f f e c t aimed

a t r e h a b i l i t a t i o n , reconst ruc t ion , development and modernizat ion . ,

of the s i x po r t s d i r e c t l y c o n t r o l l e d by t'he ~ u t h o r i t i . V i z Lagos,

. . PortHarcourt , Calabar, Warri, Burutu and KoRo.Ports.

There was considerable damage t o p o r t s i n s t a l l a t i o n and mechanical

handl ing equipment e i t h e r as a d i r e c t e f f e c t of t h e . c i v i 1 war o r as

a r e s u l t o f disuse fo l l ow ing abandonment o f operat ions i n t he war

a f f e c t e d areas. 'A p r o v i s i o n o f N4.1 m i l l i o n was made f o r t he

r e h a b i l i t a t i o n o f the p o r t s s t ruc tu res and necessary mechanical

' equi pments.

The end o f c i v i 1 war (1967 - 1970) witnessed a sharp increase i n t he . . .

coun t r y ' s i n t e r n a t i o n a l t rade and p o r t a c t i v i t i e s . The heavy imported

: . and recons t ruc t i on machinery i n c l u d i n g heavy s t ruc tu res o f ' some. bas ic

i ndus t r i es , cons t ruc t i on ma te r ia l s and consumer goods t h a t f looded the

Lagos Ports immediately a f t e r t he war were too much f o r t he capac i t y

of the p o r t s which had n o t been completed c lea red o f t he accumulated

war Cargo. (6)

Out o f 6.0 m i l l i o n tonnes passing through N iger ian Ports i n 1970 - 1971 Lagos Ports handled 5.1 m i 11 i o n tonnes o r 85%. The A u t h o r i t y

was compelled t o s e r i o u s l y t h i n k about the p o r t expansion.

-. This a c t i o n was j u s t i f i e d because the p o r t development p r o j e c t s a re

t ime consuming and invo lves very huge amounts o f fund. Therefore t h e

problem o f how much, where and when t o i n v e s t was o f c r u c i a l importance

because a mistake made may have a s&ong negat ive i n f l u e n c e f o r a l ong

t ime t o come. To t h i s end, the pre l im inary . s tud ies i n c l u d i n g the .el

engineer ing design i n connect ion w i t h the T h i r d Wharf Apapa expansion

p r o j e c t were undertaken.

Due t o the o i l boon, improved economic s i t u a t i o n and a very favourab le

balance o f payment p o s i t i o n , the count ry saw a unprecedented sharp

increase i n i t s i n t e r n a t i o n a l t r ade and p o r t a c t i v i t i e s . For ins tance

i n 1975 - 1976, 9.3 m i l l i o n tonnes o f Cargo passed through our var ious

p o r t s as aga ins t t h e .design capac i t y o f 4.1 m i l l i o n tonnes. I n e a r l y

1975, the sh ips awa i t i ng b e r t h s t a r t e d b u i l d i n g up r a p i d l y i n N ige r i an

waters. The s i t u a t i o n become u n c o n t r o l l a b l e when a t the he igh t of

t h e p o r t s congest ion i n August 1975, 455 vessels were a w a i t i n g b e r t h

a t Lagos P o r t alone. By October 1975, and i n s p i t e o f tremendous

e f f o r t made t o c l e a r t he congestion, t he re were s t i l l as many as 394

vessels c a r r y i n g about 27 m i l l i o n tofines o f Cargo, w h i l e ., the .. average

w a i t i n g t ime stood a t 180 days. Th is s i t u a t i o n arose main ly from

unprecedented i n f l u x o f cement i n bags imported i n t o t he count ry as

w e l l as t h a t o f goods meant f o r 'FESTAC' p repara t ion . (6 ) .

The Federal Government t he re fo re accorded a p r i o r i t y t o t he p o r t

development programme i n t h e t h i r d 'Na t i ona l Development Plan 1975

- 1980'. A s e r i e s o f measures c o n s i s t i n g o f both sho r t term and . . , I

l ong term ope ra t i ona l tecchniques as w e l l as p o r t development I ..

programme were planned as success fu l l y executed. .

It i s hear ten ing t o mention t h a t v i r t u a l l y a l l the major p o r t

development p r o j e c t s envisaged i n the t h i r d n a t i o n a l development

p lan have been success fu l l y completed and t h i s has t o a very g r e a t * " '

e x t e n t improved s i t u a t i o n i n N ige r i an Por ts so much t h a t no s h i p

has t o w a i t f o r b e r t h i n g beyond the i n t e r n a t i o n a l l y accepted maximum

p e r i o d o f 10 days.

The f o u r t h Na t i ona l Development P lan was t h e t ime i n which some

o f t he p r o j e c t s t h a t were n o t completed i q , t h e T h i r d Na t i ona l

Development P lan were completed. These. i n c l u d e p o r t o f Onne and

Sapele P o r t . The p o r t s development i n ~ i g e r i a c o u l d be b r o a d l y . .

c l a s s i f i e d i n t o phases:-

The f i r s t phase spanned f rom 1907 t o 1970. The c o n s t r u c t i o n i s a l l

o f g r a v i t y w a l l s o f concre te b locks, s e t i n s l opp ing bonds. These

a r e now cons idered as t h e o l d po r t s , mos t l y used. f o r Coaster vesse ls

and source c r a f t s . They a r e e a s i l y recogn ised by t h e i r t imbe r

fenders and t h e i r s t a t e o f d i s r e p a i r . Example o f these p o r t s are,

Warr i o l d p o r t , Apapa o l d p o r t , Calabar o l d p o r t , Burutu p o r t and . . . ,.

O ld Onne p o r t .

The second phase i s 1975 t o 1980. There was a has te t o develop

p o r t s due t o s h i p conges t ion i n N i g e r i a n waters. The P o r t s . .

developed i n c l u i e T incan I s l a n d por t ; Warr i n e w p o r t , Sapele p o r t ,

Calabar new p o r t and Onne p o r t , Por t -Harcour t . The mode o f

c o n s t r u c t i o n i s a deck supported by p recas t concre te p i l e s .

From 1981 t o da te t h e r e has been economic. depress ion and t h e s h i p

t r a f f i c reduced tremendously. There were ve ry few sh ips f o r t he

: numerous po r t s . As a r e s u l t o f t h i s low t r a f f i c , t h e p o r t o f Sapele

.was handed over t o t h e N i g e r i a n Navy.

There i s general- lack of a t t en t ion t o maintenance in Nigerian Ports.

The old ports a re already in bad s t a t e of repa i r , and proper a t t en t ion

i s not being paid t o the new ports e i t he r . A walk along the new

ports quay aprons will convince one of the lack o f - a t ten t ion t o these

quays and the quay infras t ructures .

CHAPTER THREE

DESCRIPTION OF THE CIVIL ENGINEERING FACILITIES AT NIGERIAN PORTS

3.1 GENERAL

E a r l i e r the e s s e n t i a l c i v i l eng ineer ing f a c i l i t i e s ... i n . t he N ige r i an ' .I "

p o r t s had been discussed. I n t h i s chapter a d e t a i l e d d e s c r i p t i o n

o f these f a c i l i t i e s w i l l be given. As has a l ready been s ta ted ,

these f a c i l i t i e s i nc lude breakwater, quays, j e t t i e s , dredge, r a i l w a y

roads, paved te rmina ls , warehouses and sheds. These i tems c o n s t i t u t e

t he e s s e n t i a l c i v i l engineer ing i n f r a s t r u c t u r e s i n t he po r t s .

The i r proper maintenance i s very impor tan t t o t he economic se rv i ce +

o f the por ts .

BREAKWATER

3.2.1 Desc r i p t i on and f u n c t i o n

A harbour i s a water area p a r t i a l l y enclosed and so p ro tec ted f rom

storms as t o p rov ide sa fe and s u i t a b l e accommodation f o r vessels. . There a re two types o f harbours, n a t u r a l and a r t i f i c a l harbour.

A n a t u r a l harbour i s i n l e t o f water area p ro tec ted f rom the

storms and waves by the n a t u r a l con f i gu ra t i on ' o f t h e land. I t s

enterance i s so formed and l oca ted as t o f a c i l i t a t e n a v i g a t i o n

whi l e ensur ing comparative q u i e t w i t h i n t he harbour. Natura l

harbours a re l oca ted i n bays, t i d a l es tua r i es and r i v e r mouth.

Warri P o r t and Koko P o r t a re good examples o f n a t u r a l harbours

i n N i g e r i a .

An a r t i f i c i a l harbour i s one which i s p r o t e c t e d f rom t h e e f f e c t s o f

waves by means break-water. Thus a breakwater cou ld be d e f i n e d , as a

; . s t r u c t u r e cons t ruc ted f o r t h e purpose o f fo rming an a r t i f i c i a l harbour

w i t h t h e water area so p r o t e c t e d f rom t h e e f f e c t s o f sea waves as t o

p rov ide s a f e accommodation f o r sh ipp ing .

3.2.2 C h a r a c t e r i s t i c f e a t u r e s

There a re many d i f f e r e n t types o f breakwaters which have been . \

c ons t ruc ted i n d i f f e r e n t p o r t s of t h e wor ld . The n a t u r a l r o c k and

concre te o r t he combinat ion o f bo th m a t e r i a l s fo rm 95% o f a l l t h e

breakwaters cons t ruc ted (1).

The Lagos channel breakwaters a re cons t ruc ted w i t h n a t u r a l rocks which

i s commonly r e f e r e e d t o as rock mound breakwaters. The e a s t Mole and

West o f Lagos harbour e n t r y a r e t y p i c a l examples o f r o c k mound break-

water.

T h e i r c o n s t r u c t i o n c o n s i s t s

r u n - ~ f f - ~ u a r r j m a t e r i a l s , p

i s p r o t e c t e d w i t h a su r f ace

and shape and l a i d t o a we1

o f a core o f sma l l e r rocks,. r e f e r e e d t o as

laced as a f i l l on t h e seabed. Th i s m a t e r i a

course o f l a r g e rocks, se lec ted as t o s i z e

1 d e f i n e d s lopes. One i n te rmed ia te l a y e r o f

sma l l e r s i zes , u s u a l l y termed the under layer o r t h e f i l l e r course

separates t h e i n n e r c o r e and t h e o u t s i d e envelope of l a r g e armour rocks.

The s i g n i f i c a n t f e a t u r e o f t he breakwater i s t he f i t t i n g and key ing

o f t he stones i n t h e armour l aye rs . The ma jo r weakness o f t h i s t ype

o f c o n s t r u c t i o n i s t h a t displacement o f a s i n g l e keystone may r e s u l t

i n _ ' f a i l u r e of complete s e c t i o n of t h e breakwater.

Generally wave break i n a depth o f water equal t o about 1.3 times t h e

wave he igh t ( 13 ) .

F i g 3:2;1 Crossect ion o f the mound as b u i l t 1907

3 . 2 . 3 Sources and causes o f damage

There i s a considerable damage t o the Lagos breakwaters. The

damage t o eas t Mole breakwater i s consid,erably smal l because o f

r e h a b i l i t a t i o n which was c a r r i e d o u t recen t l y . The breakwater

i s i n good c o n d i t i o n w i t h the except ion o f minor stone dislodgement

a t t he end o f the mole.

The West Mole breakwater i s i n a s t a t e of d i s repa i r . The main

breakwater head which has the l i g h t house has been severed see

p l a t e ( 3 : Z : l ) . This damage i s caused by washing away of t he f i n e r

ma te r i a l s l ead ing t o dislodgement accompanied w i t h some degree of

set t lement .

Present ly t he west mole breakwater r a i l i s a l s o i n a a bad s t a t e

and the mole crane i s o u t of commission. A very huge sum o f money

i s requ i red t o r e h a b i l i t a t e the s t ruc tu re .

The f a i l u r e o f breakwater has become a sub jec t of g rea t concern

cons ider ing the huge c a p i t a l invo lved i n the cons t ruc t i on and

repa i r o f breakwater,.

The e a r l i e r designs o f breakwater neglected the i n f 1 uence of

wave periods. I t i s now known t h a t wave per iods have a very

g rea t i n f l uence on the s t a b i l i t y o f breakwaters. The in f luence

o f wave pe r iod has n o t been demonstrated by the Hudson formula

o r by t h e I r i b a r r e n formula (16) . There i s a t r e n d t h a t l onge r wave

per iods g i ves r i s e t o g r e a t e r damage and thus r e q u i r e heav ie r armour

u n i t s (16) .

I n a p r o p e r l y designed and cons t ruc ted breakwater, mode t e s t (11)

demonstrated t h a t f a i l u r e s a t i d e a l i z e d sphere mounds occur a t o r

below t h e lowes t l e v e l o f wave r e t r e a t due t o h i g h normal fo rces .

The damage was most pronounced j u s t below , . .. t h e Seawater l e v e l (SWL).

A p a r t i c u l a r dangerous s i t u a t i o n e x i s t s i f resonance occur between

wave per iods and downrush per iods . Resonance r e f e r s t o t h e s i t u a t i o n

t h a t occurs when downrush i s i n a low p o s i t i o n and c o l l o p s i n g . The

b reak ing o f p l ung ing waves takes p l ace simul tanLously and repea ted l y

a t o r c l ose t o t h e low downrush p o s i t i o n caus ing peak forces

perpend icu la r t o t h e s lope. A t t he same t ime h y d r o s t a t i c p ressure

from i n s i d e t h e mound a t t a i n s a maximum valve. The 'phenomena i s we1 1

known f rom p r a c t i c a l exper iences as has been recorded on Dutch and

B r i t i s h revetments and on Norwegian breakwaters (11) .

A b e t t e r understanding o f f l ow c o n d i t i o n s d u r i n g t h i s resonance s i t u a t i o n

may be ga ined by cons ide r i ng t h e v e l o c i t y f i e l d w i t h i n a b reak ing wave,

where h i g h fo rward v e l o c i t i e s dominate.

The r a p i d change i n d i r e c t i o n o f v e l o c i t i e s i n t h e t oe . o f t h e wave causes

h i g h acce la ra t i ons . The c o n d i t i o n i s s i m i l a r when a wave breaks on a

s l o p i n g s t r u c t u r e where downrush and outward v e l o c i t i e s i n t he back p a r t

of t he t oe combine.

When downrush velocities join upward velocities in the part of the toe.

the combined velocity vector rotates. This resu l t in a. broad sustained

maximurh normal force, reaching a peak valve as the velocity vectors a re

directed almost normal to the breakwater slope. This development has , .

been demonstrated experimental ly (11).

The phenomenon clearly indicates the significance of wave period.

Negligence of th i s factor has resulted in fa i lures of many rubble , ,.

mounds and other sloping structures.

Slope s t a b i l i t y i n colessionless material under s t a t i c condition

depends upon the angle of internal f r i c t i o n of the materials in

the slope.

The potential f a i l u r e planes are nearly paralled with slope in tersect ing

i t near the toe. In the case of a breakwater where the outer surface

i s .composed of heavy armour, the angulari ty of the pieces produces a

very high angle of in ternal f r i c t i on . The lowest angqe will generally

occur in the core material .

Under dynamic conditions , wave ve loc i t i es concentrate on the outer

surface of a breakwater and t h i s has been the t rad i t iona l concern of

designers. Characteri s t i c a l ly the Huds0.n formula. (1.0) f o r the s i z e and

slope of armour deals with t h i s outer layer.

The mound i s par t i cu la r ly suscept ible t o the constant f r e t t i n g and

a t t r i t i o n of weaves. Impact and backdraught or suction cons t i tu te two

a l t e rna t ing forces which are contineously and incessantly a t work even

in time of moderate o r calm weather. Rough rubble i s smoothed and

rounded by repeated movement unt i l 1 i t i s e a s i l y sucked out position

and rol led away.

The surface slopes thus become gradually l e s s s teep while the f l a t t e r i n g

increases the power of the waves changing them more and move from osci 1 l a to ry

i n t o the t rans la to ry variety.

Considerable f a i 1 ures occured t o breakwaters a1 1 over the world.

Investigation have indicated t ha t there are three main causes of f a i l u r e

tcf Breakwaters .

( i ) Improper Design.

The f i r s t type of fa i lure i s caused by improper design. This i s

as a r e su l t of the lack of suff ic ient information about the nature

of waves in that area, lack of proper so i l investigation or wrong

interpretation of the resul ts of the so i l investigation and the

nature of construction materials. The s t a b i l i t y of rock mound

breakwater i s dependent mainly upon the weight and shape of

individual amour rock and slope on which they are la id . This .' . .

indicate that the s ize and nature of the rock are very important

factors i n the construction of rock mound breakwater. The nature

here refers to the density porousity and roughness of the rocks.

( i i ) Segregation

The second cause of fa i lure i s the washing away of the f iner

materials from underneath the large rocks. Unless the armour

rocks are la id carefully f i t t e d together so tha t i s practically

no voids, (a job which i s very d i f f i c u l t to perform because of

the i r regular i t ies of the large pieces of rocks and which i s not

considered the best practice because of i t s low permeability)

some of the f iner materials of the core may be washed away, . .

destroying the support under the armour rock and ultimately

causing i t to be dislodged resulting in the eventual collapse

of the breakwater.

In the case of a core composed of stones of small sizes :and

where only one protective covering of large stone i s provided

wave action particularly tha t of breaking wave wi 11 tend to loosen

and wash out the smaller materials through the voids.

Thus settlement and deformation will ensue with subsequent danger to

breakwater. Such a core real ly needs two protective covering. Below

the principal (outer) covering should be placed a layer'of stone graded

in s ize from large to small and completely covering the mound. This , ,

layer having a minimum of spaces and acting as a seive, will minimize

the loss of materials from the core.

I t i s very important to protect the core, unless i t i s bu i l t of.coarse

clean rock, with an under layer or f i l t e r coarse of selected rock,

which will prevent the loss of f iner materials through the larger voids

between pieces of armour rock and which will permit good.drainage of

the water l e f t behind by the backwash of waves. Unless , t h i s water can

readily escape i t may build up a high hydrostatic head which may displace

the armour rock.

The success or fa i lure of a rock mound breakwater also depends

on the principal protective covering. This also i s influenced' by the

composition, s ize of stone, thickness, slope and levels. . ,

( i i i ) Settlement

The third type of ' fa i lure i s caused by settlement. The nature of

rock mound breakwater i s such tha t i t can withstand a considerable

amount o f set t lement . The method o f cons t ruc t i on permi ts

i n t e r n a l adjustment t o take p lace w i thou t a f f e c t i n g i t s o v e r a l l

s t rength. The amount o f set t lement should be p rope r l y est imated

and a l lowed f o r i n determin ing the he igh t o f ' t h e breakwater.

When ever a rock mound breakwater i s t o be cons t ruc ted on a s o f t

bottom, i t i s impor tan t f i r s t t o p lace a l a y e r o f rock over the

bottom f o r a w id th considerably wider than the ba'se-'of t h e breakwater

The purpose o f t h i s i s t o d i s t r i b u t e the l oad over a wider base so

as t o prevent shear f a i l u r e and eros ion o f , t h e under lay ing s o i l a t . .. . . . . .

, toe o f t he roc kmound.

It i s known f a c t t h a t when the l oad placed on the s o i l exceeds i t s

bear ing va lve the s o i l w i l l f a i l by shear ing a long curved p lane

c u t t i n g the bottom a t some d is tance beyond the toe o f the super

imposed load, and causing the s o i l t o heave . i n t h a t area (1.2).

Therefore a base of s t ronger m a t e r i a l extending beyond the toe

and plane o f f a i l u r e w i 11 reduce possi b i 1 i t y o f - f a i l u r e .

The seabed on which the s t r u c t u r e has been founded mus-t n o t be

overloaded. Weak foundat ion beneath a breakwater w i 11 r e s u l t

i n l ack o f s t a b i l i t y and undue se t t lement if the under lay ing

ma te r ia l i s

s t ruc tu re .

too weak t o w i ths tand the weight imposed on i t by the

Wedges o f the m a t e r i a l s w i l l ' be displaced l a t e r a l l y ,

causing the seabed to haeve a t some distance from the toe of the

mound. This will pers is t while the so f t materials i s being.squeezed

out by the continued addittion of rubble to the mound.

Allowance fo r th i s can then be 'made i n the design of the structure

so tha t the designed height i s achieved when settlement has ceased

and can thereafter be maintained. Breakwaters constructed on the

usual firm sand and gravel of coastal s i tuat ion may have an allowance

for ultimate settlement of one or two fee t ( 2 ) . ' On the other hand

a much greater allowance may have to be made i n the case. of breakwater

founded on clay f ine sediment or the alluvial deposit of in te r ior

bays and estuaries. - Settlement of breakwater may also occur in a l l cases, due to in te r ior

consolidation. Settlement of breakwater may also occur due to scour . . ..

of the toe which must be guided against. Where structure are

founded on s-and and gravel, settlement i s l ikely to be practically

completed by the time the work i s finished. If the thickness a n d

compressi b i 1 i t y of the underlaying stratum vary considerably under

different parts of the breakwater, both the re la t ive and total

settlement .will. vary from place to place. I.. t will be r ight t o say .. .

. that the need of accurate and proper so i l .investigation cannot 'be over

emphasized.

Plate

Plate 3:2:2 Recently rehabili ted e a s t mole

Plate . . 3:2:3 East mole harbour side

Plate 3:2:4 East mole sea side

-

3: 2 :LJ. REPAIR AND MAINTENANCE OF BREAKWATERS

Several processes are invo lved i n the maintenance o f ,, breakwaters. Once the need f o r maintenance i s establ ished,

the f i r s t s tep i s t o decide on the type o f maintenance t o

be appl ied. With the knowledge of t he mechanics o f f a i l u r e

o f rock mound, t h i s f i r s t s tep would n o t be d i f f i c u l t . A t

t h i s stage the type o f ma te r i a l t o be used are a l so determined.

The second s tep invo lves es t ima t ion of the q u a n t i t y of ma te r i a l s

requi red. These ma te r ia l a re sourced and stocked i n s u f f i c i e n t

quan t i t y . It i s very important t h a t the ma te r ia l s requ i red

are stocked i n s u f f i c i e n t quant i ty 'because o f t he d is tance

invo lved i n acqu i r i ng these mater ia ls . The ma te r ia l f o r

Lagos mounds, a re obta ined from Abeokuta, a d is tance o f about

150Km from Lagos.

When the ma te r ia l s a re stocked the nex t s tep i s t o mob i l i ze

equipment and human resources. The equipments used i n

r e h a b i l i t a t i o n o f rock mounds are the mole cranes o r f l o a t i n g >

cranes. Adequate hand are requ i red t o operate the cranes and

t o secure the stones so t h a t i t couqd be l i t t e d and placed

where i t i s needed.'

The j o b i s then performed and a f t e r complet ion the s i t e i s

demobi 1 i sed.

The preserva t ion o f a mound breakwater necessi tates there fore a

p e r i o d i c replenishment of mater ia ls . This can however be reduced

b u t n o t e l iminated, by ensur ing t h a t t he rubb le s i z e are such as t o I '

reduce t h e i r movement t o a minimum.

The p i t c h i n g o f seaward slopes w i t h massive stone o r concrete b locks

goes f a r t o n e u t r a l i z e the d e s t r u c t i v e act ions, b u t the p r o t e c t i o n

provided i s n o t always completed.

As i n d i c a t e d e a r l i e r t he success o r f a i l u r e of a breakwater depends

on the s ize, s lope and he igh t o f t he p r i n c i p a l p r o t e c t i v e covering.

It i s imperat ive the re fo re t o have a double p r o t e c t i o n layers . This

prevents movement and washing away o f t he core ma te r ia l s . P la tes

3:2:2, 3:2:3 and 3:2:4 show eas t mole a f t e r r e h a b i l i t a t i o n .

F i g 3:2:2 i nd i ca tes a sec t i on o f the eas t mole a f t e r r e h a b i l i t a t i o n

F i g 3:2:1East mole a f t e r r e h a b i l i t a t i o n 1991

It would be observed t h a t t h e seas ide has been r a i s e d much above t h e

r a i l r o a d . Th i s i s because se t t l emen t occured t o a p o i n t t h a t t h e waves

c o u l d n o t be broken by t h e breakwater and i t became necessary t o

r a i s e t h e seas ide s tones f o r t h e breakwater t o per fo rm i t s f unc t i on .

Be fo re t h e r e h a b i l i t a t i o n , waves cou ld c ross t h e breakwater over t h e

t o p i n t o t h e harbour s ide .

P l a t e 3:2:1 shows West mole breakwater where t he ex tens i ve damage has

severed o f f t he head o f the mole.

I n t h e maintenance and r e c o n s t r u c t i o n o f damaged breakwater , t h e r e

i s t h e need t o i n c o r p o r a t e some l a t e s t des ign p r i n c i p l e s t h a t cou ld

be very u s e f u l i n enhancing t h e s t a b i l i t y and d u r a b i l i t y o f t h e

s t r u c t u r e . Such des ign p r i n c i p l e s a re geared towards reduc ing t h e

c o s t o f maintenance o f a breakwater and a l s o improve e f f i c i e n c y .

These p r i n c i p l e s as advocated (11) i nc l ude .

Downrush v e l o c i t i e s s h a l l be as smal l as p o s s i b l e and s t e p s lopes

o f downrush p r o f i l e s should be avoided. Uprush t h e r e f o r e must be

r e t a i n e d o r decreased.

Avo id e x c e p t i o n a l l y p r o t r u d i n g elements*.

Avoid resonance o r des ign f o r resonance between downrush and

p e r i o d and weave per iod.

Increase t h e p e r m e a b i l i t y i n o rde r t o reduce t he b u i l d i n g of . <

h y d r o s t a t i c pressures.

F r i c t i o n between armour b locks and between these b locks and t h e

w b l a y e r i s impor tan t . Angular stones should be used.

6) Slope should be most, gen t l e w h e r e des t ruc t ive forces a r e

maxi 'mum, this impl ies ' S - s h a p e g e o m e t a r y particularly, for

c o n d i t i o n s w i t h r e l a t ive ly low t i d a l w e a v e s ,

Fig 3: 2: 3 B r e a k w a t e r p r o p e r t i e s

F i g 3:2:3 shows the S-shape breakwater. The ' f a l s e ' beach BC evolves

a new breaking p o i n t a t C, which reduces run up (p lung ing waves and

ou t o f phase damping).

The impervious l a y e r FEY ,prevents i n f l o w above p o i n t E which reduces

the b u i l d up t o h y d r o s t a t i c pressure i n the mound. The impermeable

l a y e r GH, prevents backwash - o u t f l o w t o be concentrated on the breaking

po in t , where the ex terna l fo rces a re maximised.

The S-SLO~CD, makes the backwash - i n c i p i e n t breaker i n t e r a c t i o n

l ess v o i l e n t and f u r t h e r separates backwash from the r e t r e a t i n g

v e l o c i t y f i e l d i n t he toe o f t he breaking wave.

The breakwater s lope i s divi'ded i n t o th ree Zones, each w i t h the

c h a r a c t e r i s t i c b lock p rope r t i es . This r e s u l t i s more evenly exposed

s t r u c t u r e which increases s a f e t y aga ins t f a i l u r e . ' I t has been known

f o r long t h a t rubb le mound s t ruc tu res when matur ing develops a S-shape.

For instance the breakwaters a t Plymouth England and Cherbourg France

b u i l t 150 years - 200 years ago have S-shape (11).

. For every cross sec t i on however waves lower than the design

are o f no inportance, and f o r waves h ighe t than about 1,5 t

design wave the breakwater i s completely destroyed. So the

wave

imes the

var ious

breakwater cross-sect ion t o be tes ted are exposed t o a c e r t a i n , and

t o the design wave r e l a t e d p a r t o f t he t o t a l probabi 1 i ty spectrum o f

t he wave c l imate .

When one armour u n i t has moved away t h e surrounding u n i t s t end t o

move i n o rde r t o f i l l t h e c rea ted gab. It i s up t o t h e engineer t o

d e t i r m i ne when r e p a i r i s necessary.

It i s b e t t e r n o t t o r e p a i r t o o o f t e n as mob i ' l i za t i on f o r maintenance

work can be more t o s t l y than t h e r e p a i r j o b i t s e l f .

There .are t h r e e ph i losoph ies w i t h r ega rd t o t h e breakwater maintenance*

Damage can be r e p a i r e d immediate ly o r annualJy!,or;,neYer. Immediate

r e p a i r s e s p e c i a l l y t o m inor damage proves t o be h i g h l y uneconomical

i n general .

Th is phi losophy o f immediate r e p a i r i m p l i e s t h a t r e p a i r equipment i s

p u t t o work on t h e breakwater immediate ly a f t e r a damage caus ing

s torm has taken place. Such an a c t i o n w i l l a l s o expose t h e c o n s t r u c t i o n

equipment t o a h i g h r i s k o f damage, as damages n a t u r a l l y occur d u r i n g

seasons o f h i g h storm. A lso work d u r i n g s to rm i s ve ry t ed ious and : .

, . r i s k y . These f a c t o r inc rease t h e c o s t o f r e p a i r i n which case such

a c t i o n s would be j u s t i f i e d o n l y i f t h e r e i s v e r y severe damage ,'

w i t h poss i b i l i ty o f a g r e a t e r damage.

The second maintenance ph i losophy i s t o de lay r e p a i r s u n t i l a p e r i o d

o f calm weather can be expected. A breakwater s u f f e r s damage o n l y

when i t ' h a s been sub jec ted t o a s torm o f a c e r t a i n l e v e l o f i n t e n s i t y .

. Once a damage has occured, subsequent storms o f t h i s i n t e n s i t y w i l l

cause no f a r t h e r damage (12) . There fo re t h e r e i s no a d d i t i o n a l danger

d u r i n g t h e i n t e r v a l be fo re r e p a i r i s e f f ec ted .

The thi rd maintenance or better non-mai ntenance phi 1 osophy i s not

repair the breakwater a t a1 1.

In practice the second maintenace philosophy l i s t ed above i s the most

common and most reasonable. The author suggest that the Nigerian

Port Authority should adapt and use the second philosophy of

maintenance of breakwaters.

3:3 DOCKS

3:3:1 DESCRIPTION AND FUNCTION

A dock i s general term used t o descr ibe a marine s t r u c t u r e

f o r moorihg o f vessels, f o r l oad ing and unloading o f cargo and

fo r emberking and disemeberking passengers.

A wharf o r quay i s a dock which p a r a l l e l s the shore. I t i s

genera l l y contineous w i t h the shore. On the o the r hand a

bulkhead o r quaywall, wh i l e s i m i l a r t o a wharf and o f t e n

r e f e r r e d t o as such, i s backed up ground, as i t der ives i t s

name from the very nature of ho ld ing o r support ing ground i n

back o f i t .

A j e t t y i s a dock which p ro jec ts i n t o the sea. While whart

can be used f o r dock l ing on one s ide only , a j e t t y may be used

on both sides. A j e t t y i s u s u a l l y i n L o r T shape. Dolphins

a re marine s t ruc tu res f o r mooring vessels. They.are an e s s e n t i a l -.

p a r t of the f i x e d - mooring b e r t h i n g type of s t r u c t u r e now

being ex tens i ve l y used i n bul k cargo ' l oad ing i n s t a l l a t i o n s . They

are used i n combination w i t h j e t t i e s and wharves t o shorten

the l eng th o f these s t ruc tures . There are two types o f do lp ins : ? *

b reas t i ng ( o r be r th ing ) and mooring.

To ho ld the sh ip i n d i r e c t i o n norminal t o the dock a d d i t i o n a l

dolphin, mooring do lph in are prov ided o f f the bow and s tern ,

l oca ted some d is tance i n back o f the face o f the dock. They -

are prov ided w i t h bo l l a r d s '(no fender ing) .

3 : 3 : 2 Characteristics of docks

A dock could generally be classif ied into two: Wharves

or quays and j e t t i e s or piers. As described, wharves a re

structures for ship berthing that runs continous with the

shore. These structures are further c lassif ied into three

according to the i r mode of construction. These classif icat ions

are:-

(4 Blockwork Retaining Wall.

This type of wall as shown in f i g (3:3:1) i s the type of

the early whatf construction in Nigeria. The wall requires

a firm., non-erodible foundation, preferably rock or ,a s t i f f

clay. These walls were bui l t from individual blocks, the

blocks are 1 aid in horizontal courses of $1 uiceiiwor% i n

which the blocks an la id in sloping courses which allows

the quay to accommodate settlement. An example of these

type of construction could be found a t Port Harcourt.

Old Wharf and Warri old Port,

MHWS-

Fig 3:3:1 Blockwall Retaining wall

( b ) Anchored Bulkhead Wall.

Anchored steel sheet pile retaining wall as shown in Fig

(3:3:2), have been widely used for quay walls construction in

the Nigerian Ports.. The steel sheet piles are supported by the

rods attached to an anchor well located a safe distance in the

back of the face of the bulkhead. In shallow installations and

where the bottom i s of good supporting valve, the sheet piling

are driven deep enough t o act as a cantilever without benefit

of additional support.

Tie rod MLWS Turnbuckle

. . . . . . . .. .. ' ,. . , . . .' * 1 *; : .: . . -. . -. , .Sand -.fill-, . , . ... , : . ' I . " ' _ ,", . .

Dredged Level tee1 psheet pile

steel sheet unchcr piles

Fig 3: 3: 2 Anchored bulkhead wall.

(c ) Open P i l e d Wharf

An area o f por ts development was s ta r ted a t the height of p o r t

congestion i n N iger ia (1975). This resu l ted ' i n commissioning

the Tincan Is land Port, Apapa t h i r d Wharf extension and Warri

new por t . A l l these p o r t are constructed of open p i l e d . . . ..

const ruc t ion F ig (3:3:3).

The deck i s o f re in fo rced concrete. P i l es are located i n .

transverse rows o r bents and are capped by concrete g i rde rs

which d i s t r i b u t e the load t o the p i l e s from the deck framing.

Longi tudinal beams are placed a t po in ts o f concentrated loads,

such as under r a i l r o a d and crane r a i l s and warehouse walls.

Shore line < PLAN

F i g 3:3:4 Typ i ca l o i l tanker j e t t y

3:3:3 SOURCES AND CAUSES OF DAMAGE TO DOCKS

The .causes for dock failure could be classified into four.

A. Foundation failure

B Impact of ships

C Chemical action

D Natural agencies

A. Foundation Fai 1 ure

Most failures of' docks have been as a result of bad foundation.

This is due to failure to obtain sufficient data or lack of Y .

appreciation of the significance of some of the soil movement

to be expected. When walls are founded upon soil stratum

other hard rock, an accurate idea of the soil characteristics

should be obtained so as to be able to predict settlement of

soi 1 s and foundations.

Docks are frequently massive structures built as a rule on low

lying ground, on rivers or estuaries or sea coast, where the

ground may often be alluvial deposit of poor quality. :The . .. .

most elaborate calculations for the stability of docks may

be nulfied if the site information as to the ground and

subsoi 1 is either inaccurate or insufficient. The materials

should also be of very good standard and using skilled workmen

for the construction. Poor workmanship and poor quality of

materials could also lead to damage. -

€3. Impact From Ships During Berthing Process.

This i s also a very important factor in the f a i lu re of docks.

This category of fa i lure i s usaul ly caused by man, in the

course of his normal duties, such as berthing a ship or by

accident due to loss of control of the vessel. T h i s type a t

incidence occur frequently i n the docks. Damage occurs to

docks due t o excessive impacts. See plate (3:3:4).

Plate 3:3:4 Damaged j e t ty a t Apapa Dockyard

In 1989 Nigerian National Shipping Line (NNSL) River O j i co l l ided

w i t h quay a t berth 16A of t h i rd wharf extension Apapa. The

co l l i s i on caused a very ser ious damage t o the p i l e s i n t h a t

area. Quay beams and deck were a l so damaged. The incidence which

occured during berthing process costed W2.71 mill ion f o r i t s

r epa i r s and a l so a l o t of revenue was l o s t due t o the berth

being out of use fo r t h a t period. This type of damage a l so occur

often a t Alas core o i l Tanker j e t t y . Such damages r e s u l t in

breaking of the tenders, which i f not replaced immediately could

lead t o damage of the j e t t y s t ruc tu ra l members, even during

normal and accurate berthing process. I

C. Chemical Action

The chemical ac t ions causing damage t o marine s t r uc tu r e a r e due

t o the act ion of water. Sea water a t t acks marine i n s t a l l a t i o n

i n two main forms.

( i ) The action of seawater on marine concrete elements. , .

( i i ) Sea water corrosion on marine s t e e l i n s t a l l a t i ons .

(1) Action on concrete elements. Seawater .contains sul phate and

a t t acks concrete i n a manner s imi lar t o the way sulphate a t t acks

concrete. Sul phate present in seawater can reac t with hardened

cementpas te , t h e s u l p h a t e r e a c t i n g w i t h c a l c i u m h y d r o x i d e .

( ~ a ( 0 l - I ) ~ and w i t h calcium alluminate hydrate. The products of

the react ions , gypsum and calcium sul phal uminate have considerably

g rea te r volume than the compound the replace.

So the r e a c t i o n w i t h the sulphate leads t o expansion and d i s r u p t i o n

o f concrete. This p a r t i c u l a r phenomena o f expansion due t o sulphate

a t t a c k does n o t occur i n seawater. The absence o f expansion i s main ly -

. .. due t o the presence i n seawater o f a l a r g e q u a n t i t y of c h l o r i d e which

i n h i b i t es the expansion. Gypsum and calcuim s u l phoal umini t e a re more

so lub le i n a c h l o r i d e s o l u t i o n than i n water and thus leached o u t by

sea water. Although c h l o r i n e i n h i b i t concrete expansion, i t s presence

i s a l so de t r imenta l t o the s t e e l ra inforcement i n s i d e concrete; t h i s

w i l l be discussed i n d e t a i l l a t e r .

I n a d d i t i o n t o the chemical act ions, c r y s t a l l i z a t i o n of t he s a l t s i n

t he pores o f the concrete may r e s u l t i n i t s d i s r u p t i o n owing t o the

pressure exer ted by the s a l t c r y s t a l s . Because c r y s t a l 1 i z a t i o n takes

p lace a t the p o i n t o f evaporat ion of water t h i s form of a t t a c k occurs

i n the concrete above sea water l e v e l ( 3 ) .

Since however the s a l t s o l u t i o n r i s e s i n t he concrete by c a p i l layy..ac€ion

t h e a t tack takes p lace on l y when water can penetrate i n t o the concrete,

so t h a t impe<meability o f concrete i s once again the most impor tan t , .

f a c t o r .

Concrete be tween

d ry ing i s severe

. a t tacked l eas t .

t h e t i d e marks subjected t o

l y attacked, wh i l e permanent

a l t e r n a t i n g w e t t i n g and

l y immersed concrete i s

The ac tua l progress o f a t t a c k by sea water va r i es and i s slowed down

by the b lock ing o f t he pores i n t he concrete t h r ~ u ' ~ h depos i t i on o f

magnessium hydroxidegin the t r o p i c s the a t t a c k i s more rap id .

Concrete i s a t tacked by sulphate s a l t s on l y when they are i n s o l u t i o n

(2 ) and as the s a l t i s removed from water a f t e r a t t a c k i n g the concrete.

The r a t e o f a t t a c k i s dependent both on the amount of su lphate present

i n t he water and on the r a t e a t which i t i s replenished. It f o l l o w s

t h a t i f there i s no moisture movement as i n t he case w i t h impermeable

concrete, d e t e r i o i a t i o n due t o s u l phate w i 11 be less. Concrete a t tacked .,.

by sulphate has a c h a r a c t e r i s t i c w h i t i s h appearance. The damage u s u a l l y

S tar ts a t edges and corners and i s fo l lowed by progressive c rack ing and .. .

spa11 i n g which reduce the concrete t o a f r i a b l e o r even s o f t s t a t e ' (3 ) .

Man i fes ta t i on o f d e t e r i o r a t i o n on concrete

Near ly a l l the d e t e r i o r a t i o n o f concrete s t r u c t u r e i s mani fested by the

appearance of cracks. There are two main sources o f c rack ing i n concrete

s t ruc ture : - cracks caused by phys i ca l mechanism o f load, thermal movement -. and shrinkage o f concrete and c rack ing from co r ros ion o f t he reinforcement.

The co r ros ion cracks a re chemical i n na ture . . Therefore on l y co r ros ion

cracks w i l l be discussed i n t h i s sect ion.

Corrosion Cracks

.Above water, co r ros ion induced s t ress develop around rebar u n t i l

(depending on the cover thickness, bar spacing and concrete t e n s i l e

s t reng th ) cracks emanate from the co r ros ion area o f s t e e l which can

eventual l y l e a d t o spa1 1 i n g and cracking.

- 8

Finite element analysis of the s t r e s s f i e ld around the bar, measurement

of bursting forces induced into concrete holes, and accelerated

corrosion t e s t on reinforce concrete specimens and columns have been

undertake by R. D. Browneq(43). His resul ts indicated tha t

( a ) The pressure to i n i t i a t e cracking was not dependent on the cover

thickness, b u t t h i s did a f fec t the crack, the nature of the

damage and the maximum pressure achieved. Table (3 : l ) .

(b ) For corners the accelerated corrosion t e s t s showed that hard

corrosion products of less than 100 microns (0. l m m ) were suf f ic ien t

to crack the concrete, equivalent to 21 times the thickness of

steel f i g (3:3:5).

( c ) The size of crack a t the surface increased 1 inearly from 0.7 to

1.3 with an increase in depth of cover from 12fmm to 75mm f i g

(3:3:6).

:1 Effe of concrete cov ,er on bursting pressure

Ratio cover t o bar dia

%

1

Type of damage (Conti nures surface)

2

3

Cont i neours Surface

corners

Local spal l ing of cover crack Prppergated from the surface

Geometry Analysis ' .'.... . ' .

Pressure a t cra ki ng M.p.a.

Larger area of spa1 1 ing possible delamnation

Delamnation area of spa1 1 ing of reinforcement

Test r e s u l t

Max pressure

M.p.a.

3.5 3.8

4.5

4.9

6.5

9.0

Fig 3:3:5 Result from accelerated corrosion t e s t (cover)

25 5 0

Cover depth

Fig 3:3:6 Effect of cover on surface crack width

Browne's work shows that only very little corrosion of the reinforcement

is needed to damage the concrete cover and the effect of greater cover

is to delay the onset of cracking, change the type of resulting damage

and increase the size of cracks visible at the surface for the same

degree of corrosion.

Under water, there is little 1 i kel i hood of corrosion cracking accuring

in this region due to the absence of oxygen.

Corrosion Process.

It is not very long when the corrosion of concrete began to gain

attention. It is very important to know how the corrosion occurs, as

this will help in the formulation of the maintenance system.

A simple 3 factor model has been developed by Browne (43) to simulate

the key factor causing damage due to corrosion of reinforcement fig

(3:3:7)

This model has aided in the survey works and helped to explain the

process of attack Fig (4: 3: 7a) shows the primary environmental factor responsible "for corrosion of steel in concrete and Fig (333: 7b) gives a simiplified model of the process of attack.

c h l o r i d e

'42D

02

Carbonation G

Steel dispossiuation

-c

Chloride

wTer Low resistivity

4

Temperature 1-1 concrete cover

Oxygen

1

C o r r o s i o n

CB ) F i g 3:3:7 Simple corrosion model

: . ( a ) Chlorides or Carbonation has t o penetrate t o the s tee l to destroy

a lka l i protection provided by the cements.

(b ) A low e l ec t r i c a l r e s i s t i v i t y of the concrete i s required t o

permit the electrochemical corrosion processes t o occur val ues of

l ess than 10,0000 ohm can be c r i t i c a l .

( c ) Oxygen from atmosphere has to reach. the s t ee l t o allow corrosion

products t o form. The volume of corrosion products i s 2 t o 4

times the volume of- the s t ee l i t replaces causing disruption of

the concrete cover zone (43)

A1 1 the three conditions above a r e necessary fo r corrosion t o

take place. This.may be summarized fo r marine s t ruc ture as - follows:

( a ) Underwater: Chlorides may penetrate through t o the s t ee l and ye t

even with a low e l ec t r i c a l r e s i s t i v i t y of saturated concrete, the

low ava i l ab i l i t y of oxygen (10 PPm i n seawater) inh ib i te the

corrosion ra te- the cathodic reaction in the corrosion being oxygen

control .

(b ) In. the t i da l zone, as f o r the underwater zone since the cover of

concrete i s su f f i c i en t l y saturated during the t i da l cycle t o a c t

as a bar r ie r t o oxygen ingress. However prolonged drying out period

in the upper t i da l zone during drain down periods in dry docks can

permit corrosion.

(c) Above the tidal zone this i s the most vulnerable zone as the

moisture content i s likely to be high, resulting in low concrete

resistivity.

High s a l t deposition'on surfaces can combine with rapid chloride

penetration to the steel i f the concrete qua1 i ty and cover are

inadequate and oxygen penetration through the unsaturated concrete

cover zone i s very rapid.

Carbonation penetration into marine structures was no t considered

t o be important due t o the presence of choride and their greater

speed of penetration. The cr i t ica l chloride level a t the

reinforcement surface to cause loss of alkali protection was

taken as 0.4% chloride (43) by weight of cement in the concrete

mix. Thus aggregate content does not play any major role in the

chemistry of the attack process,for above water condition the

time for chloride to penetrate through the cover zone to reach

the cr i t ica l chloride level a t the outer reinforcement depends

on the s a l t build up in the concrete surface and the diffusion

rate of the chloride ions through the concrete cover.

The concrete, i f dry can absorb sea water which on drying out

leaves the s a l t in the outer layers of the concrete,the amount

depending on the surface absorptivity. The absorptivity i s

primarily related to

a The concrete mix

b The degree of curing

c The degree of compaction cover zone. -

Cor ros ion o f Marine S tee l I n s t a l l a t i o n s

The s u b j e c t o f t h e d u r a b i l i t y o f meta l s t r u c t u r e s exposed t o atmospheric

and aqueous agencies i s one o f v i t a l importance i n dock and harbour

engineer ing. I n t he f i r s t p lace i t i s o n l y w i t h i n p a s t cen tu ry t h a t -?.

i r o n began t o g a i n t he pre-eminence enjoyed by wood and s tone i n

mar i t ime cons t ruc t i on , and s t e e l was an i nnova t i on o f s t i l l l a t e r date.

Consequently t h e r e has o n l y j u s t e lapsed a s u f f i c i e n t l e n g t h o f t ime

f o r r e l i a b l e da ta t o be acqu i red on t h e de te rm ina t i on o f t h e a c t u a l l i f e

o f m e t t a l l i c s t r u c t u r e s and more p a r t i c u l a r l y s t e e l i n va r i ous cond i t i ons .

V a r i a t i o n i n atmospheric c o n d i t i o n i s ext remely g rea t , the seasons be ing

marked by g r e a t f l u c t u a t i o n s i n sunshine, r a i n f a l l and temperature, n o t

o n l y f o r d i f f e r e n t seasons i n t he same year , b u t f o r t h e same season

i n consecut ive years.

The ques t i on i s s t i l l f u r t h e r compl i ca ted by t h e f a c t o r o f l o c a l i t y .

As rega rd t he aqueous i n f l uence , t h e r e i s no d e f i n i t e s tandard o f

comparisons. The s a l i n i t y , a c i d i t y , d e n s i t y and temperature o f sea

water d i f f e r s i n " a lmost every u n i t volume, so t h a t i t i s never p r e c i s e l y

t h e same a t any two po r t s . Ocean c u r r e n t s a l s o co 'n t r ibu te t o modify

t he chemical composi t ion o f t he sea.

Thenard i n 1819 ( 2 ) expressed t h e o p i n i o n t h a t r u s t i n g i s an e l e c t r o -

chemical phenomenon, w h i l s t Davy proposed t he use o f i r o n and z i n c

t o a f f o r d e lec t rochemica l p r o t e c t i o n t o copper aga ins t c o r r o s i o n by

seawater.

Another electrochemical interpretation of corrosion was p u t forward by

mallet in 1838 and the writings of faraday are fu l l of emphasis on the

essential connection between voltaic current and chemical action.

Since then four theories of immersed corrosion have been advanced, namely - the acid, the hydrogen peroxide, the coll idal and the electrochemical

theories.

Nature and Mechanism of s teel corrosion.

By definit ion corrosion the wastage of metals which i s now known to

be caused not only by chemical reactions b u t a lso by electrochemical

agencies. This problem of corrosion has been given attention recently

due to the huge loss of money incurred when corrosion takes place. The

huge loss of capital has made i t necessary to control corrosion of s t ee l .

The corrosion and -preservation of metals i s subject of great complexity

which cannot be adequately deal t with in a t r ea t i se such as th is . The

nature of corrosion of metals may be stated as the i r constant e f fo r t to

revert to the s table conditions of the mineral (5) . The reduction of

a metal from-its natural s t a t e of combination w i t h other elements i s

a achieved by the expenditure of energy and i t follows that only in the

so called 'noble' metals headed by gold i s the mettall ic ' s ta te naturally

stable. The tendency of a metal to corrode may be expressed quanti tavely

by the amount of energy 1 ibrated in change from the mettall i c to the

- oxidised s t a t e , by the standard electrodes potential of the metal.

The standard or.hydrogen sca le o f p o t e n t i a l i s t h a t i n which the .

p o t e n t i a l s between blackened p la t inum satura ted w i t h hydrogen under

one atmosphere pressure and an a c i d s o l u t i o n o f normal hydrogen

concent ra t ion i s taken a s s z e r o j u s t as the temperature of f r e e z i n g

water i s taken as zero on the cont igrade thermometer. By ar rang ing

the metals i n order o f t h e i r normal e lec t rode p o t e n t i a l we ge t what i s

known as the e lect rochemical ser ies .

Electrochemical se r i es

Metal Noble end (ca thod ic o r p ro tec ted end)

Go1 d

S i 1 ver

Copper

Hydrogen

Lead

T i n

I r o n

Zinc

Aluminium

Magnes i um

10n considered Normal p o t e n t i a l

e lec t rode ( V o l t s )

L i thum L i -3.02

(Base end Corroded end) Table 3:2 Electochemical se r i es

Neither the r a t e nor the mode of corrosion in a given environment can

be inferred from t h i s table 3:2 otherwise the corrosion problem would

. . be simpler than i t i s . I t i s necessary to consider other fac tor super

imposed upon the i n i t i a l c,orrosion tendencies a s represented by the

values in the table fo r example the extreme react iv iness of the

alluminium under normal conditions leads t o the formation oxide f i lm

(alumina) which e f fec t ive ly suppresses continued a t t ack upon the metals

beneath i t . The same action occurs t o some extent with a l l metals (2)

Analysing the causes of corrosion of immersed metals, the l ib ra t ion

of energy which occurs when corrosion takes place i s accompanied by

a redis t r ibut ion of electrons which, i f conditions a re favourable,

may produce detactable e l e c t r i c current .

This can be visualised by considering a simple vo l ta ic c e l l , a l l the

features of which have t h e i r counterparts in ordinary immersed F

corrosion, though separate anodes and cathode cannot always be usually

distinguished.

Elect rolyte i

Anode 1 1 t Caltode

- Fig. (3:3:8) Simple Voltaic Cell

E

- - + M e t + HS- --t

- .

, E 2

The co r ros ion process may be regarded as caused by the i n t e r a c t i o n of

anodic and cathodic components.

The v o l t a i c c e l l ( t h e e l e c t r o l y t e being a d i l u t e a c i d s o l u t i o n )

represents the hydrogen e v o l u t i o n type o f co r ros ion i n which co r ros ion

i s a f u n c t i o n o f the amount o f hydrogen evolved. Here the cathodic

r e a c t i o n may be represented as fo l lows.

2E + 2H+ - 2H + Hz

Hydrogen e v o l u t i o n co r ros ion i s normal l y associated w i t h a c i d i c

i n d u s t r i a l waters.

l a t i o n of e lec t rons a t I n neu t ra l s a l t so lu t ions , however the accumu

the Cathode occurs (except w i t h very r e a c t i v e metals) o n l y i n t he

presence o f oxygem,which becomes reduced t o the equat ion

2E + 0 + H20 - 2 ( 6 ~ ) - I

This c o n s t i t u t e s the'oxygen absorp t ion type o f corros ion. I n the more

general case i n which a l k a l i n e s a l t s a re present, the fo rmat ion o f

, . hydroxylions a t t he Cathode must occupy w i t h the format ion o f f r e e a l k a l i .

U.R. Evans ( 2 ) descr ibe experiment by which i t may be shown q u i t e

dea r l y t h a t t he mechanism o f co r ros ion o f metals i s e lect rochemical i n

character and t h a t the fou r main p a r t s o f the process can be demonstrated

as fol lows:,

(1) The product ion o f an e l e c t r i c c u r r e n t

(2 ) The product ion o f a so lub le m e t a l l i c s a l t ( c h l o r i d e ) a t t he anode

(unaerated) places

(3) The product ion o f a1 k a l i (hydroxide) a t t he cathodic (aerated)

places and -

(4) The precipitation of an insoluble hydroxyl where the products

from the caihodic and anodic areas meet.

For instance with iron immersed in a solution of sodium chloride

the primary anodic products is a soluble iron chloride and the

cathodic products is sodium hydroxide. By precipitation we get

white ferrous hydroxide, but in the presence of oxygen this

rapidly oxidises and becomes green on the lower surface, (ferric

hydroxide), thus forming the mixture of iron hydroxide which

we know as rust.

Controlling factor in immersed corrosion.

The agent by which the course of corrosion may be influenced are

of many kinds and may be conveniently classified as "Promoting

and Control ling" factors or those associated with the metal and

those connected with the environment.

The former include for example, electrode potential and' surface

condition including internal stresses. The actual amount of

corrosion almost invariably fails to reach the calculated value a

and thus it is recognised that there are control 1 ing factors at

work which have some influence in restricting the corrosion attack

on the metal. In immersed corrosion these may be associated with

the complex phenomenon associated with "hydrogen over potential " . In the case of atmospheric exposure, humidity provides the

electrolyte and in industrial atmosphere this is invariably

acidic in character (5).

Experiment by Frjend J.N. (2) established the linkage between immersed

corrosion and atmosphere oxidation. By progressively increasing the

speed of movement of aerated water over steel, he showed that the

rate of corrosion increased, but when the critical speed of movement

was reached the increase in corrosion gave place to falling valves.

Increasing the speed still further, it was found that complete

inhibition of corrosion occured, the specimen removing quite bright

and rustless.

Vernon W.H.J. (2) has shown by experiment the effect of progressively

increasing rebtive humidity on the corrosion of iron specimen with

and without the presence of atmospheric pollution and the curves in

fig 3:3:9 gives the results.

Air pollutkd with O.Ole/. of wlphor and partic:les of charcoal.

I

I

i r pol 7 dioxide

~ t e d w i t h o n l y .

0.01% of sulphor

Progressive increasing r e l a t i v e humidity per cent

Fig. 3:3:9 C r i t i c a l humidity: Influence o f humidity and atmospheric p o l l u t i o n on the rus t ing of m i ld s t e e l .

A i r

- 4'-- +. - // \ rust

Scale ca l tode m o l t ' FecIp \ NeoIt

' F ig 3:3:10 Mechanism o f p i t t i n g

He points out that:-

a. A t r e l a t i ve humidities l e s s t ha t 60% there i s no v i s i b l e change, *

whether the a i r i s polluted or not and t ha t u p to t h i s level of

humidity, f i lm formation i s predominant.

b. Within the range of 60 - 80% some rusting occurs and the f i lm

i s evidently breaking down.

c. When t h i s c r i t i c a l humidity range exceeded there i s r e l a t i ve ly

enormous increase in the r a t e of corrosion provided only t ha t

t races of pollution are present. Curve C shows the added e f f e c t

of ammonium sulphate, the typical consi tuent of ordinary sol id

atmospheric pollution.

. C D i s t r i bu t i ono fco r ro s ion

With regard t o the d i s t r ibu t ion of corrosion the simplest and

l e a s t dangerous i s t ha t of corrosion d i s t r ibu ted uniformly

over the whole surface of metal. Localised corrosion however,

when i t takes the form of p i t t i ng , may lead to more or l e s s

rapid perforation. Fig. (3:3: 10) indicates ' what occurs in .such

cases in neutral solution o r natural water, i . e the formation of

a film or scale which i s capable of act ing as a cathode when the

underlying metal becomes exposed a t any point forming anode areas. . ..

While the cathodic area i s protected, the danger of the s i t ua t i on

a r i s e s from the f a c t t ha t oxygen reaching the r e l a t i ve ly large

area of the metal surface functioning cathodically may d i r ec t l y G

contribute t o the corrosion of the small anodic areas.

An important f ea tu re of the formation of r u s t i s t h a t i t s presence

may a f f ec t fu r the r corrosion i n two d i f fe ren t ways.

A layer of dr ied rust may tend t o protect the metal just below i t

and a id a t t ack upon areas ' immediately surrounding i t by functioning

possibly as the cathodic members of the electrochemical system.

On the other hand the wet parch of the rust i s usually favourable t o

the continued corrosion of the metal beneath i t , mainly due t o the

shielding of i t from oxygen so rendering i t anodic. The actual

d i s t r ibu t ion of anodic and cathodic areas i s determined by the par t

which the d i s t r ibu t ion of the dissolved oxygen may play and i s the

basis of the d i f f e r en t i a l aera t ion pr inciple associated with the work

of .Dr . U.R. Evan ( 2 ) .

Apar t from the development of cathodic and anodic areas due t o the

e f f e c t of d i f f e r en t i a l aera t ion var ia t ion in s a l i n i t y a l so e f f e c t s

the d i s t r ibu t ion of corrosion on mari time s t ruc tu re .

Corrosion of s t ee l occurs i n four zones: e a r t h , water, t i d a l zone

and splash zone.

Atmosphere

Sp lash Zone

, - d -

High t i d e

_..- L o w t i d e .c 0

c Quiet w a t e r m u d l ine

I

20

F i g 3:3:11 Typ ica l co r ros ion r a t e o f s t e e l MPY m u i l l m e t r per year

Corros ion r a t e o f s t e e l sheet p i l e i n sea i s g rea tes t i n t h e sp lash

zone because o f t he a1 t e r n a t e l y w e t t i n g and d r y i n g and a l s o a v a i l a b i l i t y

o f oxygen (5) . F i g 3:3:11. a

The r a t e o f metal d e t r i o r a t i o n i n t he sp lash zone i s a l s o dependent

on whether t he re a re contaminat ing agent' i n t he water o r no t . For

example c lean sea water w i l l promote i t s h ighes t r a t e o f c o r r o s i o n

i n t h e splash zone reaching valves o f 15 (rnpy) (2 ) . I f contaminated

w i t h o i l o r o the r organic m a t e r i a l s t he co r ros ion decreases i n t h e sp lash

zone. The lowest co r ros ion r a t e w i l l be found i n t he e a r t h zone.

However, h i g h l y reducing s o i 1 bottom (anaerobic) beneath h i g h l y o x i d i z i n g

water (aerated) can encourage the k i n d o f co r ros ion which r e s u l t i n

r a p i d metal l oss and in tense p i t t i n g corros ion.

The failure of fish wharf at Tincan Island port was found to be as '

a result of corrosion of the steel sheet pile. Part of the steel sheet

pile was perforated and it allowed the movement of sand from behind

the

due

not

quay into the water. This created a large cavity failure occured rn

to the fact that the support en4 was eroded and the slab could

support itself as a cantilever. This is a typical example of

lack of inspection and maintenance.

With proper maintenance orogramme this could have been remediet

at very little cost.

P l a t e 3:3:5 C o l l a p s e d due t o cor roded s h e e t p i l e

P l a t e 3:3:5 showing c o l l a p s e d quays deck due t o c o r r o s i o n a t Tincan I s l a n d po r t .

Microbiological Corrosion.

Underground 'corrosion i s seen to be a problem of equal importance

to the atmospheric corr osion.

Corrosion of cas t iron takes the form of graphitization and may occur

for example when the metal in form of pipe i s buried in impervious

clays and even when laid a t great depth in the sea, though there i s

evidence that in fresh water th i s form of corrosion does not occur.

The following examples of immersion corrosion in water are of

: . in te res t , ' cas t iron cannon from a vessel which had sunk in the

fresh water of Delware r iver for more than 40 years were perfectly . ..*.

free from any corrosion. On the other hand the cast iron work of

the royal George and the Edger sunk in the sea fo r 133 years and

62 years respectively were found to have become quite so f t and

damaged. The wrought iron was not so much damaged except where

in contact with copper, brass or gun metal " ( 2 ) .

Judged exclusively from the stand point of the electrochemical - - . - . .

theory, such resul ts are apparently incompatible for i t would be

expected tha t , under condition in which the* ra te of oxygen supply ,. t . .

must have been excessively small, the specimen of cas t iron in the

sea water would have suffered a l i t t l e deterioration as those in -

fresh water. Hence one i s led to conclude tha t the graphitisation

of the cast iron in sea water and underground i s direct ly associated

with condition which on the electrochemical theory, should lead

t o immunity of corrosion, t ha t i s t o say i t i s actually favoured .

by the exclusion of oxygen.

Anomalous r e s u l t s such as these remained unsolved f o r many years

indeed t h e i r s i g n i f i c a n c e was n o t suspected u n t i l i n 1934 a Dutch

S c i e n t i s t Wolzoger Kuhrs (2 ) . Suggested as a p o s s i b l e exp lana t i on

o f t h e a c t i o n o f anaerobic su lpha te reduc ing b a c t e r i a which i n h i s

view, i t ac ted as hydrogenacceptor and p rov ided a medium f o r t he

d isposa l o f t h e ca thod i c hydrogen, a r o l e norma l l y f i l l e d by

atmospheric oxygen. Research i n t h i s f i e l d o f obse rva t i on was

taken up and Kuhrs view were con f i rmed i n p r i n c i p l e .

L a t e r exper iments have shown t h a t i n n e u t r a l s o l u t i o n f rom which

oxygen i s excluded, c o r r o s i o n occured o n l y i n t h e presence of

bac te r i a . U n c e r t a i n t y s t i l l e x i s t s , however as t o whether t he .. , su lpha te s imp ly takes t he p lace o f oxygen i n o r d i n a r y ae rob i c

c o r r o s i o n under n e u t r a l cond i t i ons .

Anaerobic b a c t e r i a o f t h e su lpha te reduc ing types such as v i b r o

d i s u l phate u t i c a n s a r e known t o e x i s t i n c e r t a i n areas o f t h e sea

bottom.

What i s of liruch g r e a t e r s i g n i f i c a n c e i s t h e f a c t t h a t they. ,a lso

f l o u r i s h i n many impervious c l ays , and i t i s t r u e t h a t t he m a j o r i t y

o f c l a y s o i 1s c o n t a i n a1 1 t he c o n d i t i o n s f a v o u r i n g m i c r o b i o l o g i c a l

co r ros ion . Exc lus ion o f oxygen and t h e presence o f su lpha te and

o f b a c t e r i a a r e t h e c o n d i t i o n f avou rab le f o r such co r ros ion .

P l a t e 3:3:6 Dolphin damaged by corros ion

P la t e 3:3 :7 Abondoned j e t t y due t o cor ros ion damage 7

4. Na tu ra l Agencies

There a r e t h r e e impor tan t agencies t h a t a r e o f concern t o t he

docks and i n s t a l l a t i o n s . They a r e t h e a c t i o n s of wind, waves

and cu r ren t s . 4

Cons ider ing t h e wind f a c t o r , t h e f o r c e s exe r ted by t h e wind

i s o f t e n s u f f i c i e n t t o impede o r even p reven t t he manoevering

o f sh ips . Occas iona l l y acc iden ts happen through t h e b reak ing

of mooring 1 i n e s f rom excess ive s t r a i n , and loses have occured

where a l l t he l i n e s go t broken, each l i n e snapping i n qu i ck

succession l e a v i n g t he vessel e n t i r e l y he lp less .

Another f a c t o r where wind c o u l d be cons idered i s when t h e r e

i s a h i g h wind over a l a r g e area, whicn c o u l d l e a d t o t h e

development o f t i d a l waves.

Wave i s t h e o n l y n a t u r a l agency which r e q u i r e s g r e a t concern.

The e f f e c t o f wind pressure upon t he supe rs t ruc tu re o f a j e t t y

i s t r i f l i n g compared w i t h t h a t o f t h e onse t o f waves upon i t

base. The o n l y danger t o be apprehended f rom c u r r e n t s i s t h e i r

tendency t o undermine t h e foundat ion , l rn less t h e p i l e s ' a r e

d r i v e n t o depth below t h e i n f l u e n c e o f waves as they would be

i n normal cond i t i ons .

A1 though waves have been d i v i d e d i n t o two c lasses, those of

t r a n s l a t i o n and those o f o s c i l l a t i o n . I t i s probable t h a t a l l

waves a r e more o r l e s s waves o f t r a n s l a t i o n , caus ing t h e p a r t i c l e

o f which t hey a r e composed t o move fo rward h o r i z o n t a l l y t o -

some ex ten t .

Th is i s t h e case w i t h a l l waves l a r g e enough t o e f f e c t t h e s t a b i l i t y

o f mar i t ime works such as j e t t i e s .

I f a wave before b reak ing reaches w a l l o r o t h e r o b s t r u c t i o n s hav ing

an abrup t v e r t i c a l face, i t i s r e f l e c t e d i n such a manner as t o produce

t h e f o l l o w i n g e f f e c t s . The p a r t i c l e s move up and down th rough a h e i g h t

double t h e h e i g h t o f t he o r i g i n a l wave. A t a d i s t ance away f rom

the w a l l equal t o t h e q u a r t e r o f t h e l e n g t h o f t h e wave. The p a r t i c l e s

move h o r i z o n t a l l y backward and forward. Between these two p o i n t s

t he mot ion o f t he p-tides i s a compound one and t he movement takes

p lace a t va r i ous angles. Consequently t h e a c t i o n o f waves upon a

p i e r o r j e t t y must be taken as r e s u l t i n g i n t h e c r e a t i o n o f f o u r

d i s t a n t forces.

a ) A d i r e c t h o r i z o n t a l f o r c e e x e r t i n g compression.

b ) A d e f l e c t e d v e r t i c a l f o r ce , a c t i n g upwards and tend ing t o shear

any p r o j e c t i o n beyond t h e su r f ace o f con tac t .

c ) A v e r t i c a l downward fo rce upon t h e base o f t he w a l l due t o t h e

c o l l a p s e o f t h e wave. . d) The s u c t i o n o f t h e back draught upon t h e foundat ion .

Apar t f rom t h e h y d r o s t a t i c pressure argumented t o very cons ide rab le

degree by t he f o r c e o f impact t h e f o l l o w i n g s u b s i d i a r y r e s u l t s w i l l

t ake p lace.

1) A v i b r a t i o n of t he s t u c t u r e t end ing t o weaken t h e connect ions

of va r i ous p a r t s .

A s e r i e s o f ' impu lses communicated t o p a r t i c l e s o f water con ta ined '.

i n t h e pores o r j o i n t s of t h e s t r u c t u r e p roduc ing i n t e r n a l

: . r 1 pressure i n va r i ous

The a1 t e r n a t i v e compression and expans

d i r e c t i o n s .

i o n o f a i r conta

i n c a v i t i e s caus ing d i s r u p t i o n ,

i ned

3:3:4 Repa

The

74

irs and Maintenance of docks.

two major materials used in the construction of docks

are concrete and steel. The concrete could be in the form

of mass, reinforced or prestressed concrete. Concrete is the

most used materials. The other material is steel which is

employed in form of sheet pile or stanchions. The maintenance

of docks will be discussed under two major headings:-, The

maintenance of marine concrete element and the maintenance

of steel element, this is to make it easier since all dock

structures are either of concrete or steel or the combination - of both.

A. Maintenance of concrete

Concrete structures in marine environment have been designed - , .

on the assumption that they would be maintenance free for their

operating life. This assumption has not been achieved due to

problems, some not forseen at the desigg stage. Such problems

include failure due to stress concentration, accident's and

recently more epidemic factor, the corrosion of reinforcement

in concrete. The maintenance of concrete could now be classified

into three:

i . Repair to concrete

ii. Production

iii. Specification

The f i r s t r e f e r s t o a c t u a l r e p a i r work and r e c o n s t r u c t i o n o f

damage concre te s t r u c t u r e s . Whi le t h e l a t e r two, p r o t e c t i o n and

s p e c i f i c a t i o n r e f e r t o t h e l a t e s t means o f ach iev ing a more du rab le

concrete.

1 Repai r o f concre te

A f t e r p roper i n s p e c t i o n and t e s t i n g a programme o f r e p a i r i s

formulated. A1 1 f a i 1 ures o f r e i n f o r c e d concre te a r e evidenced .

by c rack fo rmat ion .

There fo re r e p a i r works a r e e i t h e r normal c rack r e p a i r o r corroded

s t e e l r e p a i r .

The types o f cracks t h a t cou ld be r e p a i r e d i n c l u d e p l a s t i c sh r inkage

cracks which occur when concre te su r f ace i s exposed t o s a l t , i t

happens immediate ly a f t e r c o n s t r u c t i o n .

P l a s t i c s e t t l emerit c racks a r e cracks i n r e c e n t l y c a s t concrete.

I t c o u l d be sealed immediate ly when loca ted .

-.

shear and t r ansve rse cracks: - Cracks o f t h i s t ype have been caused

by s t r e s s and which have n o t y e t a l lowed s i g n i f i c a n t con tamina t ion

' t o e n t e r o r co rbonat ion t o t ake place. They a r e sealed by i n j e c t i o n . .

: . o f r e s i n s i f they a r e i n a c t i v e o r can be widen a t t he su r f ace and

sea led w i t h j o i n t s e a l a n t i f they a r e a c t i v e .

7 6

Where cracks i s l i v e and continous to move w i t h changing load

or temperature, i t cannot be glued together with res in . If the

concrete i s uncontaminated the cracks must be widened a t the surface , .

and sealed as a j o in t . Where the concrete i s carbonated or

contaminated with chloride. I t must be broken out and replace

and sealed movement jo in t s formed a t the same time.

Repair of corroded s tee l in concrete

Once s tee l corrosion has been noticed there are products which

primarily require the damaged concrete t o be broken out to expose

the s t e e l . The s tee l i s cleaned and coated t o insula te i t

electrochemically from fur the r a t t a ck , and a dense concrete mortar

used to res tore the sect ion. There i s need a lso to coat the whole

surface t o seal adjacent areas agains t fu r the r penetration and

damaged and t o avoid a s h i f t i n the ac t ive areas as a r e su l t of

a i r .

'Plate 3:3:8 cover cleaning of reinforcement ..

Plate 3:3:9 Cover cleaning for repair of corroded s t e e l .

11 P r o t e c t i o n

Where the concrete m a t e r i a l a v a i l a b l e o r t h e workmanship and

s i t e superv is ion are l i k e l y t o be the best, concrete cou ld be

used f o r p r o t e c t i o n aga ins t cor ros ion .

I r o n sheet'permanent shu t te rs compatible w i t h concrete, may

prove t o be very c o s t e f f e c t i v e p e r m i t t i n g the use o f a cover . . ..

q u a l i t y o r s t r e n g t h grade concrete y e t e f f i c i e n t f o r s t r u c t u r a l

need.

Hydrophobic (water p roo f ing) admixture based on t e s t s (53)

have shown t h a t these can slow down c h l o r i d e i r o n d i f f u s i o n and

reduce absorp t ion t o a n e g l i g i b l e amount p a r t i c u l a 1 . r ~ a t low

cement content.

Water r e p e l l a n t sur faces t reatment such as s i l ances and sixonanes

make the ou te r few m i l l i m e t r e o f the cement hydrophobic. F i l m

forming coat ings such as expoxies and polyurethanes appl i e d t o

t he concrete surface. When app l i ed t o a c a r e f u l l y , blow ho le 1

f r e e sur face, c e r t a i n coa t ings can make the concrete t o t a l l y

impervious t o c h l o r i d e s and s i g n i f i c a n ' t l y reduce t h e Pate o f . . , .

oxygen d i f f u s i o n t e s t have shown t h a t a 0.3mm coa t i ng can be

equ i va len t of e x t r a 500mm o f concrete cover i n terms o f s lowing

oxygen d i f f u s i o n (44). A

: . Epoxy coated rebars have been found t o be very successful i n , t h , e

p r o t e c t i o n o f marine s t r u c t u r e s i n h o t environment l i k e N iger ia ,

t h a t even the normal requirement f o r h igh q u a l i t y concrete, a

l a r g e cover depth and h igh standard of s i t e c o n t r o l may prove . .

unnecessary.

111 I n the l a s t 10-15 years new s p e c i f i c a t i o n and code o f p r a c t i c e

have been in t roduced f o r the design o f marine s t ruc tu res .

Off-share codes are i n general agreement on a minimum cement

con ten t of 400Kg/m3 (43) f o r t he most severelextreme exposure

cond i t i ons i n the sp lash zone and a maximum w/c r a t i o o f 0.4.

Considering cover t o re inforcement ,once again the codes r e f l e c t

d i f f e r i n g opin ions as t o the s e v e r i t y o f exposures i n the d i f f e r e n t

Zones. BS 6235 considers t he atmospheric zone t o be as severeas . ,

the sp lash zone (75mm), w i t h the submerged zone l oss sever (6Omm).

Dn V however, s p e c i f i e s the same cover f o r bo th submerged and

splash zones (50mm) w i t h t h e atmospheric zone considered as l e s s

severe (40mm). A C I t r e a t s bo th t he atmospheric and submerged zones

as l e s s severe than the sp lash zone, w h i l s t t he norwegian petromeum

d i r e c t o r a t e t r e a t a1 1 zones the same (50mm). BS 8110 s p e c i f i e s

(60mm) f o r sp lash zone. (43)

Ch lo r ide l e v e l s a re a l lowed t o a maximum o f 0 . 3 5 % by weight o f

cement.

Crack are c o n t r o l l e d by maximum w id th o r maximum s t e e l .. s t r e s s .. where

the crack width, i s the governing c r i t e r i a , the 1 i m i t i n g w id th a

e i t h e r 0.3mm o r 0.004 times the cover. -

B Maintenance of marine steel installations

The damage to marine steel infrastructure could be classified

as failure due to structural defect and failure due to corrosion.

If the structure is bulkhead forming the waterside perimeter of

a marine terminal damage is often the result of vessel impact.

Steel structures which are exposed to marine environment for any

length of time and are not protected either by coating or cathodic

protect system are usually affected corrosion.

1 Structural Repair

Having established a need for repair or strengthing, the

overall repair concept must be developed having regard for

the performance requirement, the installation method and costs.

The major cost in any repair will be in the subsea work and the

provision of,, support vessels during instal lation, and therefore

the reduction of these phase of the work must ..be a primary

objective in selecting the repair concept. The method of repair

chosen must provide for flexibility in installation, whilst

not relying heavely on diverse workmanshi p.

Repai r Methods

a) Bol ted Repai rs

Bolting has not been used frequently in the repair of marine

structures defects. This is due to the fact that bolted repairs

require an accurate fabrication necessary to ensure that the new

pieces can be fabricated and bolted to the existing structure.

? Such a fabrication must be proceeded by extremely accurate survey.

.. .

Never the less, b o l t s a re employed when i t becomes q u i t e necessary.

Most ly due t o i n favou rab le cond i t i ons f o r t he o the r methods.

(b ) Welded Repairs

Welded r e p a i r s a re o f t e n pre fered f o r marine s t ruc tu res , b u t i t

always very expensive. The area t o be welded has t o be conta ined

w i t h i n an enclosure which can be a subsea b e l l ( a h a b i t a t ) o r a

cofferdam open t o the atmosthere above the water l i n e . I n each

case the enclosure ( l a r g e enough t o con ta in the work space f o r

a t l e a s t one person) needs t o be purpose b u i l t t o f i t the

p a r t i c u l a r p a r t o f the s t r u c t u r e t h a t i s being repai red.

( c ) Clamped Repair

This techniques uses a c y l i n d e r i c a l clamp t o surround an

e x i s t i n g member, t he clamp i s genera l l y formed i n two

l o n g i t u d i n a l pieces, sometime i n th ree o r more pieces.

The clamp component are b o l t e d together and load i s

t rans fe red from the o r i g i n a l member t o the clamp by f r i c t i o n .

A new member can be at tached t o the clamp t o take the l o a d

elsewhere, o r the clamp can be used t o t r a n s f e r l oad across

a d i s c o n t i n u i t y (a crack o r dent) i n the o r i g i n a l member.

The s imp les t clamp r e l i e s on f r i c t i o n development between the ou te r face o f t he e x i s t i n g s t e e l and the i nne r face of

the s t e e l clamp. The most successful subsea clamp has an

i nne r diameter some 100-150mm ( 4 ) g rea ter than the diameter

o f the member i t i s sorrounding. The annulus i s f i l l e d w i t h

g rout and load i t t rans fe red from the o r i g i n a l member through

tlhe grout t o the clamp i t s e l f .

(d) Corroded Steel Repair

A f t e r t he s t r u c t u r a l ana lys is t o determine the type o f r e p a i r

requ i red has been done. I f the d e t e r i o r a t i o n has n o t caused

any overs t ress ing i n the remaining s t e e l a s imple r e p a i r w i l l

be e f f i c i e n t . - -.

, A. ~ 3 . 9 : 3.3: 12 Unstressed grouted clamp

0 . F i g 3:3:12 Mechanical clamp

C. Fig 3:3:12 Clamp on steel members.

In t h q c a s e of simple repair evaluation of the remaining useful i I .

life of the structure must be made to determine what measures - 1

I ,;

must be taken t o m i t i g a t e con t inued c o r r o s i o n perhaps o n l y s imp le ho le

pa t ch ing i s r equ i red . Several methods have been employed t o pa tch ho les

i n s t e e l sheet p i l e . Metal p l a t e s e i t h e r welded o r b o l t e d t o t he s t e e l

have been used success fu l l y . A s i m i l a r t ype o f r e p a i r and l e s s expensive

i s t o f i l l t he ho le w i t h concre te t o g rou t . F i g (3:3:13) i l l u s t r a t e s a

t y p i c a l r e p a i r d e t a i l (38).

detail ( 3 8 ) .

F i g 3:3:13 Patch Fepa i r o f sheet p i l e s t e e l . ( s e c t i o n )

The geogtechnica l f a b r i c i s used t o p rov ide a p o s i t i v e r e s i s t a n c e when

pumping t h e conrete. I f no s i g n i f i c a n t word e x i s t s t he f a b r i c c o u l d be

o m i t t e d i n s i t u a t i o n where t h e a n a l y s i s o f t h e sheet p i l e i n d i c a t e d t h a t

some ove rs t ress ing ( g r e a t e r than a l l owab le and l e s s than y e i l d ) e x i s t a

' r e p a i r method must be developed which cou ld e l i m i n a t e t h e ove rs t ress ing .

There are several ways which the reduc t i on i n s t ress can be accomplished.

One method o f reducing i s t o reduce load. An unusual r e p a i r which can

reduce s t ress i n t he sheet p i l e and the anchor system o f a t i e d back i s

i l l u s t r a t e d i n F i g (3:3: 14).

Existing wale deadman

hole in sheet pib Ccnt~nues concrete patch.

.

F i g 3:3:14 T ie back bulkhead r e p a i r ~ i g h t w e i g h t ' b a c k f i l l

Corrosion caused holes i n the sheet p i l e a t t he mean water l e v e l

(mw), as a r e s u l t o f the cor ros ion the remaining sec t ion o f the sheet

p i l e was overstressed. This r e p a i r patches the e x i s t i n g ho le by

p lac ing a concrete p lug behind the sheet p i l e i n the area of maximum

corros ion. I t a l s o reduce s t ress i n the sheet p i l e by r e p l a c i n g the

gravel (heavy weight) b a c k f i l l w i t h an expanded shale (H igh t weigth)

backf i 11. I :

The reduct ion i n e a r t h pressure by reducing and decreasing the a c t i v e

c o e f f i c i e n t because o f the character o f t he l i g h t weigth f i l l brought

the bending s t ress i n sheet p i l e w i t h i n t o l e r a b l e l i m i t .

General l y sheet p i l e r e p a i r s a re more o f t e n replacement type repa i r s .

New sheet p i l e s a r e d r i v e n around the e x i s t i n g c e l l and the annular

space i s f i l l e d w i t h gravel o r concrete.

An i nnova t i ve r e p a i r techniques developed f o r c e l l u l a r s t ruc tu res

u t i l i z e s the concept of placement o f new sheet p i l e around the

e x i s t i n g s t ruc tu re , b u t ins tead o f d r i v i n g the new sheet i n t o the

bottom, on l y p a r t i a l l eng th are used. ' T h i s r e p a i r r e a l i zes the

capac i ty o f the r e l a t i v e l y uncorroded p o r t i o n o f the sheets i n the

zone o f h igh loop tens ion and l i m i t e s the r e p a i r t o t he d e t e r i a r a t e d

area. See Fig. (3:3:15)

B i g 3:3:15 PLAN (A) ..

Fig 3:3:15 Ceclular sheet pi le repair ( Section) I3

Another repair technique which more appropriately should be called a

replacement i s i 1 lustrated below. The repair should be considered only

when analysis of existing conditions indicates severe overstressing and

the required useful 1 i f e cannot be achieved .with simple repair or 1 imited

structural repair .' Specif ical ly th i s repair i s accompl ished shoreward of

the bulkhead s t ructure which means i t will not encroach on available

water side uses, such as vessel berth.

Fig 3:3:16 Steel sheet pi le bulkhead replacement

This repair i s generally slow since continuous instal la t ion of the new

steel sheet piling i s not possible. The new anchor must be placed pvior

to instal la t ion of the new sheet piling. The new.sheet pi les around the

existing t i e rods should then be instal led. This technique allows the

new anchor wale to be placed providing yestraint of the new sheets.

After the majority of the new sheets are in place the sheet which were

placed b u t not driven a t the old t i e rod locdtion must be driven . The

old t i e i s cut and the new sheet driven.

Steel Protection.

Maritime structures of cast iron and steelwork have to withstand

corrosive conditions which has been already discussed. I n respect -

to dock instal la t ions , bui 1 ding and structures generally, together

with marine structures the following may be seen as the principal

preventive measures which may be employed to protect steelwork from

corrosion.

1) Design of Steelwork for Corrosion Resistance

Where the s teel stucture or parts of i t are subjected to

varying high and low t ide levels , the most important consideration

i s tha t of ensuring that the outer surfaces are completely

accessible for the application of subsequent protective coatings.

Steelwork should have no pockets where water can col lect .

2 ) Preparation of Surfaces

The f i r s t consideration to ensure successful protection i s the

complete removal of a l l mill-scale form steel section. This

varies in i t s tenacity of adhesion to the metal t o which i t i s

cathodic i-n action, and unless completely removed may cause

pi t t ing as a resu l t of electrochemical action.

In addition to the 8tlhW b u t quite effective method or removing

mill scale and rus t such as picking in an acid, chipping, hammering

and wire brushing-sand or shot-blasting of members and flame

cleaning before and a f t e r assembly and erection are useful

modern procedures.

Organic Coat ing

The c o s t o f e f f i c i e n t p repara t ion o f s teelwork surfaces, together

w i t h t h a t o f the a p p l i c a t i o n o f coat ings i s f a r i n excess o f t he

c o s t o f pa in ts . I t fo l l ows the re fo re t h a t c a r e f u l cons idera t ion

must be g iven t o the s e l e c t i o n o f t he most appropr ia te coa t i ng

f o r the p a r t i c u l a r s t r u c t u r e and the co r ros ion cond i t i ons i t w i l l

have t o withstand, i n order t h a t the expense e n t a i l e d i n

p repara t ion w i l l n o t be wasted. The use o f the c o r r e c t p r im ing

coat and i t s c a r e f u l a p p l i c a t i o n a f t e r p repara t ion o f t he sur faces

are the most important steps i n p rov id ing and e f f i c i e n t organic

p r o t e c t i v e coat ing. Some of the usual organic coatings i nc lude

pa in ts , l i t h o - o i l , w i t h i r o n oxide, l e a d chromate pa in t s c o a l t e r

and asphal t .

Cement and Concrete

Cement and concrete cou ld a l so be used as p r o t e c t i o n f o r s tee l ,

sometimes i n form o f c a s t i n g and re in fo rced concrete.

Me t ta l i c Coat ing . I n cons ider ing metal coat ings the dock engineer w i l l normal ly

be concerned o n l y w i t h those f o r the preserva t ion o f i r o n - and

s t e e l . The bes t known method i s o f course galvanis ing, b u t

t he cos t o f t h i s i s somewhat h igh and precludes i t s use on the

main members o f s t ruc tu res , w i t h which we are here main ly concerned.

Cathodic P ro tec t i on

As we have discussed the co r ros ion process i s i n most cases

e lect rochemical and made up the anodic and cathodic components

wbich can be in f luenced by appropr ia te means.

Cathodic protection is in effect the control of the mechanism of

the corrosion process. - -. -- - .

A anode C Original Caltode

AA auxillar y (external) anode

Fig 3:3: 17 Cathodic protection

The principle of Cathodic protection involves the application of

a counter electric current opposing that responsible for corrosion

thus rendering'the whole structure cathodic. The essence of cathodic

protection is that it prevents ions leaving the surface of bare

metal and becoming ultimately oxidised, that is to say forming rust.

In the diagram A,and C represent the anodes and cathodes of a system

undergoing corrosion, the A zone corrodes because they continual ly

provide electrons to make good the deficiency in the C zone. If an

auxiliary external anode AA, that is to say an external source of

electron is set up. Corrosion of the A zone will cease if the supply

of elearons from AA to C is equal to that previously forth-coming A.

I n other words i f the originals cathode C are polorised to the same

negative e l ec t r i c potential as the original anodes. Any further

increase in the superimposed e.m.f. will s t i l l further depress the

joint potential of the origirial A and C zones.

Two methods of applying the necessary superimposed current are

possible in practice.!Structures of iron or s teel e i ther who1 ly immersed

or part.ially immersed or buried i n the ground may have a cathodic

current of suff ic ient density and E.M.F. impressed upon them e i ther

by ( a ) the use of external anodes of magnesium, alluminium or zinc

or by (b) anodes of scrap iron or grahpi'te may be used, the necessary

current being supplied by an external anode are sac r i f i c i a l , tha t

i s t o say they themselves are dissipated on corroded .,areas Snstead of the

anodic areas of the structure.

c able electrtcally currerut fLow comected t o jetty lhrough metel

. . m a g x s i u n anode

'r - v v e

Fig. (3:3:18) Cathodic protection to a j e t ty by ga.1 vanic process

..

1.

C m t fLw through water

1

unslrlaied cable

A

Current f low L Ihrw* water .

4-

F i g 3:3:19 Cathodic p r o t e c t i o n t o a j e t t y us ing power impressed method.

3.4 . -Dredging

3:4:1 General. - A simple d e f i n i t i o n o f dredging i s t h a t i t i s t he subaqueous

excavat ion o f so i 1 and rocks (45). The process c o n s i s t o f t he

excavation, t ranspor t and subsequent d isposal o r use o f the

ma te r ia l dredged. Since i t occurs underwater, i t i s o u t

o f s i g h t and genera l l y t he app rec ia t i on o f t he need f o r and

complexi ty o f dredging i s l i t t l e upderstood.

The importance of dredging i s to increase the channel depth of

waterways so as to provide access to ports and harbours. In

case of riverinpi8 navigation, dredging i s required to construct

and maintain v i ta l navigation works to inland ports and

f a c i l i t i e s .

Dredging i t s e l f i s essent ial ly an excavating operation, b u t

the use of the correct equipment i s vi ta l in achieving economy.

All dredging ac t iv i t i e s ca l l fo r special consideration of the

nature of the ground to be dredged, the best means of removing

so i l sp and the optimum work programme.

3.4.2 Types of dredgers

Dredgers are broadly c lass i f ied into three based on the i r

mode of excavation and operation. They are mechanical dredgers,

hydraulic dredgers and mechanical/hydraulic dredgers which

ut i 1 ize both basic elements in some combination. Within these

three categories further subdivision can be made on the basis

of propulsion; tha t i s , those which are self-propelled e i ther . during the excavation phase, the transportation phase or both

and those which are non-sel f-propel led. The production ratef

for the dredger varies widely depending on the circumstances,

the material to be dredge and the transport and disposal methods

employed. Other factors such as weather and sea s t a t e , ship

t r a f f i c , depth, depth of the dredging face also a f fec t dredging

production ra tes , therefore they can range form 50 cubic metres

to 4000 cubic metre per hour (45) .

Mechanical Dredgers

Thi,s category employs mechanical means for the excavation of

material and are generally similar to the equipment used for dry

1 and excavation. Examples of mechanical dredgers are:

Grab or clamshell and dragline Fig. (3:4:1).

These employ either rotating cabs or fixed frame type barge-

mounted equipment, which have hoisting and control systems and

use clamshell digging devices or buckets rigged on cables to

excavate the material from the bottom and transport it vertically

out of the water and into barges for subsequent transport to

a disposal area. Clamshell dredgers can be used in sandy

types of clay, gravel cobbles and some broken rock dredging

situations. They are not particulal effective in fine silts

which have a tendency to run out of the bucket but are nonetheless

used for this purpose in smaller jobs.

One advantage of clamshell dredgers is their ability to dredge in

fairly deep waters and their ability to do precise spot dredging a

either to remove isolated areas above grade in the channel or

along docks and corners of docks. Depending. on the type of

material dredged, they are normal ly non-sel f propel led and are

fixed at the excavation site using anchors or spuds- - . --.- -- .-. . - -

96

b. Back Hoe Dredger

The back hoe f i g (3:4:2) is common t o dry land excava tors and i s

i nc reas ing ly being employed f o r dredging. They a r e barges-mounted

f o r dredging, gene ra l l y non-self p rope l led and can have moderate

product ion r a t e s . The m a t e r i a l s excavated i s brought t o t h e

s u r f a c e and placed i n - b a r g e s f o r t r a n s p o r t t o t h e d i sposa l a r ea .

They can d i g a broad range of m a t e r i a l s such a s s and , ' c l ays ,

g r ave l , cobbles and f r a c t u r e d and unf rac tured moderately hard

rock. They have r a d i u s and depth l i m i t a t i o n . They a r e a l s o

f i x e d by anchors o r spuds. 7-- .- . . ..

, . .. . . -. - . .. . ' '. . - $5 .&7>..i.*. .._, t i & h ..

ig 3:4:2 Back hoe dredger

c . Dipper dredger f i g (3:4:3) i s more o r less a powered shovel

mounted on a - b a r g e . Older vers ions used a r o t a t i n g boom wi th

a s t i c k and shovel design.

Late? designs incorpora te the r o t a t i n g cab, l i t t i n g beam and

a s t i c k and bucket. These dredges use v e r t i c a l ' spuds t o anchor

them t o the bottom and a d igg ing spud t o the r e a r o f t he vessel

t o p rov ide res is tance t o the massive d igg ing fo rces o f the bucket.

The dredger operated by us ing t e e t h on the l i p o f the bucket t o

excavate the ma te r ia l f rom the bottom, once the bucket i s f u l l

t he d ipper s t i c k i s withdrawn upwards and the cab and bottom

r o t a t e d so the bucket i s over the barge o r scow, the bottom o f t h e

bucket i s re leased. thereby dumping the content o f t he bucket i n t o

the barge.

Dipper dredgers are p a r t i c u l a r l y s u i t e d f o r dredging hard rock

and h i g h l y compacted ma te r ia l and have been used e f f e c t i v e l y

i n removing o l d subsequeous foundations from w i t h i n the p ro jec t . - - - -- -- - - - --- - - - --

Fig. 3:4:3 Dipper Dredger.

' d . Bucket - ladder D,redger

Bucket-ladder dredger fig (3:4:4) once comprised a major part of

the European dredging fleet and are in fact the direct descendants

of the historic mud mills,. They use a series of buckets mounted

t o an endless chain loop. The loop is powered causing the bucket

to travel in such manner as t o scope the material from the

bottom, carry the material in the upright buckests u p the ladder

t o the t o p of the ladder where the buckets then rotate into an

upside down position thereby dumping their content into a chute.

The material is then sent through the chutes to barges alongside

the dredger. These dredgers are some times self-propelled t o

provide transport to the dredging site. They have very low

production rates and need anchor 1 i nes , which sometimes hampers

navigation; They have very high noise level.

Fig 3:4:4 Bucket ladder dredger

2. Hydraul i c Dredgers

These dredgers use hyd rau l i c c e n t r i f u g a l pumps t o prov ide the

excavat ion force, w i t h o r w i thou t mechanical c u t t e r s and hydraul i c

t ranspor t f o rce t o c a r r y s l u r r i e d s o l i d s from the d igg ing s i t e ,

through a p i p e l i n e t o the sur face and thence through a discharge

p i p e l i n e t o the d isposal s i t e .

a. P l a i n Suct ion Dredger

The p l a i n suc t i on dredger f i g . (3:4:5) can d i g a t g rea t depth

us ing ladder mounted a t deeper depth.

They a re e f f e c t i v e i n unconsol idated m a t e r i a l s such as sands and

gravels and a re used ex tens i ve l y i n aggregate winning operat ions

and l a r g e rec lamat ion p ro jec ts .

Because o f t h e i r i n a b i 1 i t y t o handle Consol i da ted ma te r ia l s and

t h e i r c h a r a c t e r i s t i c t o produce smal l deep excavation, they a re

r a r e l y s u i t a b l e o r used f o r channel o r harbour p ro jec ts . They

can be both s t a t i o n e r y o f s e l f p rope l led . I n s u i t a b l e ma te r i a l s ,

-. Fig*1!3;.4:5 P l a i n suc t ion .dredger

b. Dustpan Dredger,

A rather special type of suction dredger called the dustpan

dredger fig (3:4:6) i s used on river system where there are high

bed loads of sand sma,ll gravel and which when conditions are

right, from bars in the navigational channels.. The dustpan

are capable of moving large volumes of material from localised

areas using a suction head shaped much like a dustpan. The

material i s usually slurried by used of water jets along the

t o p of the digging face of the dustpan, drawn into the suction

head and up the suction pipeline through the pump and thence

through a relatively short floating discharge line.

Fig 3:4:6 Dustpan dredger

*

c. Water Injection Dredger

A1 though this type of process has ben known for sometimes and

utilized in special circumstance, the water injection fig (3:4:7)

is finding some notable successes primarily for maintenance dredging

at current time. The dredger uses water pressure to fluidize at

current time. -

The dredger uses water pressure t o f l u i d i z e t h e ma te r ia l t o be removed

c rea t ing a dense f l u i d s l u r r y . The s l u r r y i s then t ransported from

the excavation s i t e by means of cur rents w i the r induced by the dens i t y

g rad ient between the s l u r r y and t h a t o f water, o r by n a t u r a l l y

occur ing c u r r e n t s h t h e r induced by the dens i t y g rad ient between

the s l u r r y and t h a t o f water, o r by n a t u r a l l y occur ing cur rents

w i t h i n the dredging s i t e , such as t i d a l currents. This i s a

r e l a t i v e l y low cos t dredging technique which i s l i m i t e d t o s i l t s

and unconsol i da ted lay and f i n e sand.

-.

. . , . . . 2+r , : ,

, ,, "

I.' .

Fig. 3:4:7 Water i n j e c t i o n dredger

3. Mechanical /Hydraul i c Dredgers

These type of dredges include the real work horses of the

dredging industry. The cutter or cutter head dredger, bucket

wheel dredger and t rai 1 i ng hopper dredger. These dredgers are

employed on construction and maintenance projects depending on

the nature and quantities of material to be excavated.

a . Cutter-head and Bucket Wheel Dredger

Both the cutter-head f ig (3:4:8) and bucket wheel dredgers f ig

(3:4: 9) use rotating mechanical devices, cal led cutters mounted

ahead of the suction head t o excavate the material into suitably

sized material which i s the sucked in the suction pipe as a

slurry and pumped t o the surface. By use of pumps mounted on

the ladder or structural' device which extends.to the bottom,

these dredgers can dig effectively a t depth approaching 25-30

metres. They are characterised by high production rates and

abil i ty to effectively dig sui t , clays, sand, gravel cobbles,

fractured and sound rocks. They work in a stationery mode with 7

on spuds or anchors. They have flexible disposa; alternatives

and can either discharge into barges or' as i s generally the case,

through discharge pipes to the disposal s i t e .

Fig. 3:4:8 Cutter head dredger ___- ..

Fig. 3 : 4 : 9 Bucket wheel dredger

b. Trail ing Hopper Dredger

Trai 1 ing hopper dredgers f i g ( 3 : 4 : 10) are se l f propel led ships

with hoppers or dredged material storage internal t o the hul l ,

which have ar t iculated dredging or drag arms which extended to

the bottom to be excavated. They dredge while underway travel 1 ing

a t low speed. The drag head can be passive or active. In the

case of the passive draghead, no additional power i s applied a t

the scouring of the material to be excavated by hydraulic current

induced a t the drag head. The active draghead employs power t o

drive e i ther cu t te rs or water j e t s t o excavate material and aid

in slurrying the material. The weight contact with the bottom

material in e i ther passive or active draghead then allows the

material to be transported hydraulically as a slurry.

Trailing hopper dredgers are quite f lex ib le in terms of the

material to be dredged, i t s disposal alternatives and the a b i l i t y

to work in protected and unprotected waters. The material i s

transported internally into hoppers within the vessel to a

disposal S i t e remote from the work s i t e and e i ther dumped through

doors or valves in the hopper bottom.

Fig. 3:4: 10 Trail ing hopper dredger.

The ,Nigerian Ports Authority has the biggest dredger in West African

Coast (sea Lion). It is a trailing hopper dredger with a capacity ,

The rate of dredging depends on the specific gravity of the sand.

It has a maximum depth of 20m.

4. Agitation Dredging

Agitation dredging is one of the oldest forms of dredging. In its

principle, the bottom material is disturbed with the expectation that

the current will carry it away. This method therefore depends on the

presence of a current and increases its efficiency with the swiftness

at the currents (20). 5

3:4:3 Bottom materials a

In maintenance dredging the materials found consist predominantly of si 1 t,

mud or sand and sometimes gravel cobbles and rock with varying amount

of pollutant and debris intermixed. With the exception oP :r;ocls; the

bottem..materials in most dredging projects range in density from

slightly less than 1,300kg/m3 to slightly more than 200kg/m3 and occur

frequently near both ends of this range. The upper end consist

predominantly of sand and the lower end of silt or mud.

In light maintenance, materials of the bottom waterway may consist

of a several foot thick transition layer which gradually changes from

water at the top to stilt mud at the bottom. Since dredging is concerned

with materials forming the bottom, they are usually defined as to their

dredge pbi 1 i ty .

3:4:4 Disposal of dredged materials

The ultimate step in the dredging process i s to dispose or

deposit the dredged material in a location away form that

excavated. There are numbers of disposal a1 ternatives. The

basic options are: open water, inter t idal or shoreline and

up1 and or on-shore s i tes.

In each option there are further options to e i ther confine the

material or leave i t unconfined. The option or options employed

depend on a number of factors , such as; accessibi l i ty to the

work s i t e , type of dredger and transport system, whether the

dredged material contains contaminants, cost and environmental

factors. I t i s always desirabl be to use the dredged material

for beneficial purpose. Such purposes may be create f a s t land

for subsequent construction purposes as the case with Lagos

dredged materials .

When used for beneficial purposes there i s generally a cost

benefit t o be achieved thereby reducing the actual cost fo r

navigation purposes. If beneficial uses are not possible,

e i ther because of nature, volume or contamination of the

dredged' material, then disposal should be conducted in a manner

which creates minimum environmental damage . I _ ' - C s ..

3:4:5 Operat ion and Maintenance

The complet ion o f the execut ion o r cons t ruc t i on phase has

' now provided the phys ica l assets o f the p r o j e c t . There i s

a need t o have developed and i n p lace an operat ions and

maintenance scheme f o r t he completed p r o j e c t and a c l e a r

d e f i n i t i o n between the cons t ruc t i on and opera t ion and

mai ntenance phase. On 1 arge p r o j e c t s where segments may

be accepted as complete by the owner, maintenance may

even be requ i red on t h a t completed segment before complet ion

of t he e n t i r e p r o j e c t .

Much o f what i s requ i red f o r such a scheme can be drawn

from the p lanning and engineer ing phases.

But i n the case o f dredging, there seems t o be a tendency

t o over look o r minimize the importance o f subsequent

maintenance o f completed nav iga t i on p ro jec ts . Maintenance

costs can be s i g n i f i c a n t and a re recu r r i ng . Unless p r o v i s i o n

has been made t o adequately main ta in the p ro jec ts , i t s use

w i l l be l i m i t e d over a mat te r of t ime as na tu ra l fo rces such

as s i l t a t i o n reduce p r o j e c t dimension and l i m i t the use and

e f fec t i veness o f the p ro jec t .

It i s obvious t h a t such l i m i t a t i o n s w i l l s e r i o u s l y impact t he a b i l i t y

t o meet f i n a n c i n g o b l i g a t i o n s and t h e p r ima ry p r o j e c t purposes. The

maintenance scheme should i n c l u d e n o t o n l y t h e n a v i g a t i o n f ea tu res ,

b u t s t r u c t u r a l f e a t u r e such as n a v i g a t i o n a l a ids .

A modern technique which have become ind ispensab le a i d f o r a l l

ex tens i ve dredging and e s p e c i a l l y f o r maintenance work, i s t he

s e t t i n g o f h i g h performance r a d i o l o c a l i z a t i o n system. Th i s enables

accura te and f r e q u e n t soundings t o f o l l o w t h e progress o f bot tom

bed work, sounding, every month on about 18,000,000m2 and s t r i c k

con t inues p o s i t i o n i n g o f dredger (34).

t o b u i

a t o t a

annual

(35)

The approximate annual maintenance dredging i n LagosIApapa bas i s l

and channel about 8km be fo re 1979 was 5OO,OOOm2(35). The d e c i s i o n

I d T incan p o r t , t h e channel was increased f rom 8mm t o 11.51~1,

1 of 28.3 m i l l i o n cub i c metre o f m a t e r i a l was removed. Today

maintenance dredging i s es t imated a t 1.5 m i l l i o n c u b i c metres

Emergency d e c i s i o n t o b u i l d a new P o r t w i t h o u t t ime t o c a r r y o u t

t h e consequencies l ead t o h i g h problem. As dredgers and d redg ing

equipments a r e becoming more and more s o p h i s t i c a t e d and of course

more and more c o s t l y t o b u i l d , t h e a t t e n d a n t problem become

mu1 t i p 1 ied .

From the design t o const ruc t ion stages we r e l y heav i ly on

Consultants. Even i n some cases f o r the operat ion o f these dredgers.

I n t h i s respect there i s a need f o r Niger ian Por t Author i ty t o get

involved technolog ica l ly i n ' t h i s specia l i sed f i e 1 d i n order t o

remove the obvious disadvantage present ly being experienced by

a l lowing those w i t h the know-how t o cont ro l the indust ry obsolute ly.

4:5 Port Roads and Railways

3:5:1 Port Roads

There is the need f o r adequate road network system i n the

ports f o r easy 'movement of cargo. There is now a high

increase of cargo f o r export as well as from import,

These cargo need a proper road network system t o be able

t o reach t h e i r destination within or outside the port.

Ports , l i k e Tincan Island have proper road network fo r

cargo movement.

The development of motor t ranspor t f o r commercial purposes

soon proved t h a t a th in surface of tar red stone has l a s t i ng

qua1 i t y where t r a f f i c is 1 igh t , but road subjected t o

heavy concentrated t r a f f i c consis t of a reinforced

concrete base w i t h e i t h e r no surfacing material o r w i t h

a surface of two grade a s p h a l t . An example of such i s * '

the Adekunle way of Apapa Third Wharf Extension.

1 t i s a l so important t o note gradient in ports a r e of

course unusual and a r e determined-by the character of each

loca l i ty . The width of the road a l so var ies depending

on the t r a f f i c and avai lable space.

The junction of roads a r e provided w i t h e a s i l y negot-iable

curves t o allow long vehicle t o turn into and out of each

road without having t o pass over the center l i n e of double

t r a f f i c port roads.

3:5: 11 Failure of ,dock roads

I. In our observation there i s a type of dock pavement f a i lu re

which i s different from the types of fa i lure on highway,'this

type of fa i lure i.s' caused by s t a t i c overstressing' of the dock

pavement.

Due to what i s called 'load and park' in bulk cargos of

d i rec t delivery; The trucks load and park w i t h the cargos

before obtaining custom clearance. In most cases the trucks

queue u p a t the gate, some of the trucks carrying u p to 120

tons of cargo and parked on the same place for up to ten days.

In a l l Nigerian Ports the road approaching the ex i t s a re

usually damaged f i r s t .

Failure Due to Faulty Design

The sat isfactory design of a concr.ete road structure involves

two principles requirements namely, a road structure of adequate

thickness having regard to nature of the subgrade and type of

t r a f f i c and joint which are correctly spaced and of adequate

design (15). Some of the f a i lu re , due to faul ty designs are:-

Cracking of the slabs

Cracking occurs most frequently in the transverse direction;

th i s i s usually due to the s lab being too long so the warping

caused by temperature gradient i s unduly restrained.

b Failure of the Subgrade

I f the road structure i s of insuff ic ient thickness the so i l below

P may be overstressed and a non e l a s t i c deformation will occur.

c. Settlement of Subgrade

Thus may occur as a r e su l t of non uniform or incomplete compaction

during construction or changes or moisture content afterwards.

d. Mud-pumping a t Jo in t '

Mud-pumping consist of the ejection from joints , during the

passage of t r a f f i c , of water carrying f ine particles of subgrade

soi 1.

Subgrade so i l the trouble usually occurs on f ine grained so i l

only and begins when water enters the subgrade trough a poorly

sealed joint.

3. Failure Due to Faulty Materials and Workmenship

Low quality cement and poor aggregate will resu l t in weak concrete

which will not be able to withstand the desired s t r e s s .

I t i s not uncommon to find the bottom layers of manually compacted

road, badly honey combed.

4. FailureyDue to Weather

The weather may be the cause of a number of defects in concrete

roads surface, water may enter the subgrade, soften i t and cause

mud-pumping. Change i n temperature and moisture content in

concrete roads will s e t u p s t r e s s in the slab and cases have

been recorded where roads constructed so may years before opening

to t r a f f i c have cracked d u r i n g the intrim period. (9 ) .

Abrasion by Traffic

Abrasion results from the movement of vehicles wheels over the

wearing surface which result in the gradual wearing of the

vehicle tyres. The roads becomes _slippery sand dangerous.

Port road Maintenance

The port road in Nigerian Ports are constructed of concrete

roads with ashphalt covering. The maintenance of port roads

is purely the maintenance of concrete roads. It is worthy to

mention here that the port management should make it a policy

to confine the trucks to the truck terminals. The trucks should

not be allowed to litter the port road indiscriminately. Until

* a truck is cleared before it should be allowed to the gate.

In the case of damage, repair to the concrete roads becomes

necessary either when'extensive full-depth cracking occur due

to faulty design or inadequate maintenance, or when there is

some spalling of the surface. When the concrete is cracked.

It is necessary to replace the whole or part of a slab, but . when the damage consist only of surface spalling the area may

be patched.

Replacement of failed Areas

The cause of the damage should be ascertained before the repair

- are carried out and if possible the cause should be removed

Particular attention should be paid to the thorough compaction

of the subgrade, espe ially near the edges and corners.

It has been found t h a t replaced s labs a re u s u a l l y weaker than the

s lab e x i s t i n g on the road (9). For t h i s reason the use of a heavier

weight o f re inforcement than woul d normal l y be requ i red i s recommended.

It i s genera l l y b e t t e r t o rep lace the whole s l a b r a t h e r than on1y.a

pa r t , b u t i n e i t h e r case the cons t ruc t i on o f t he new j o i n t should be

c a r r i e d o u t c a r e f u l ly. Where dowel l e d j o i n t were used, i n the o r i g i ~ n a l

cons t ruc t i on every e f f o r t should be made t o expose t h e dowel led bars ,

so t h a t ' they can be strengthened, c l ianed, coated w i t h t h i n l a y e r

of bitumen, proveded w i t h cap . b u i l t i n t o the new slab.

When.only p a r t o f a s lab i s t o be replaced the cracks should n o t be

used as the end o f the replacement because the concrete on e i t h e r

s ide of" the c rack i s u s u a l l y damaged and the r e p a i r should i nc lude

those places which, a1 though they appear s a t i s f a c t o r i r y g i ve a ho l low

d u l l sound when knocked.

Patching o f Slabs

When, normal ly as a r e s u l t o f poor workmanship o r mater ia ls , s p a l l i n g

occurs on t i e sur face o f a concrete road, the method o f r e p a i r has

genera l l y been t o cbver t he whole sur face w i t h a bitumeneous carpet .

Small patche5 o f b i tumeneous ma te r ia l s have n o t been found t o be

s a t i s f a c t o r y except as temporary r e p a i r s and ob jec t i onab le a e s t h e t i c a l l y .

'Tests have been c a r r i e d o u t i n the l a s t few years, t h e r e f o r e t o

examine whether i t i s poss ib le t o patch the spa l l ed areas w i t h mortar

o r concrete i n o rder t o reduce the Cost o f r e p a i r when scaled areas are

r e l . a t i v e l y small. 7

The amount of maintenance required by a we1 1 designed and we1 1

constructed concrete road is small. More attention should however

be given to maintenance so that the defects can be treated at an

early stage and the amount of deterioration reduced. The importance

of keeping the joints and cracks properly sealed is emphasised and

method are described for raising sunken slabs, roughening surfaces

which have become smooth, repairing cracked areas and patching

spalled slabs and joints. .

1 3:5:2 ' Port railways q

! ' Railway system used to be the best way of moving large

cargo to and from the ports. Rail system can move a large

consignment a t the same time thereby making the consignee

feel quite safe comparing to lorry tracks travelling

different ly a t different speeds and arriving differently.

In the early days of port development i n Nigeria there

were few tarred roads, making road system quite inef f ic ien t*

Railway system was incorporated in the design of the premier part of Nigeria (Apapa Port).

Railway was used for the haulage of coal from Enugu and

groundnut from the Northern parts of Nigeria.

Port ra i 1 system a1 lowed the easy movement of the cargos

to the quays for export.

The general function of dock railway and siddings are

namely to provide areas in which ,

1) Railway wagons may be exchanged between the main1 ine

rai 1 system and the port r a i l systems.

( 2 Inward bound cargo wagons may be sorted to berth,

t r a n s i t shed or warehouses and made up into t ra ins

for placing a t these destinations within the dock.

ip

3) Yagons ;l!aving the docks may be sorted i n to t r a i n order, where '' possible, in to marshal 1 ing 'yard order o r Sta t ion order ready f o r t

handing over t o the main1 ine railway system. In the port of

Lagos Apapa quays, the quay s ide and the sheds and warehouses

a re a1 1 provided with a good network of r a i l system.

The r a i l t racks on quays a re l a id on a mat of reinforced concrete.

After 1aying.they are f i l l e d in t o the level of the top of the

r a i l with concrete, thus ensuring t h a t the r a i l s o f fe r no obstacle

t o the passage of road vehicles. The tracks a re guarded throughout

usually w i t h e i t h e r r a i l s o r bulb angles but occasionally w i t h

ro l l ed s t ee l channel so as t o keep the flange way groove f r e e form

obstruction. Away from the quay and shed the r a i l s a r e placed on

sleepers and bal l a s t . These areas a r e ,away from motorable areas.

The sleepers a r e l a id on ba l las t . The ba l l a s t i s t o provide

drainage and d i s t r i bu t e the load t o the subgrade.

P l a t e 3:5: 1 Warehouse r a i l w a y system appap p o r t .

P la te 3.5:2 Rai lway system i n an undeveloped p a r t of

apapa p o r t . ".

3.5.2.1 F a i l u r e o f p o r t ra i lway

a. Corrosion o f the s t e e l and i r o n pa r t s leads t o

d e t e r i o r a t i o n and damage t o the ra i lway system.

b. Sleepers are made o f t imber the re fo re some t ime r o t t i n g

and decay occurs which leads t o f a i l u r e .

c. F a i l u r e o f t he b a l l a s t t o d i s t r i b u t e the load over the

area. This usua l l y leads t o warping o f the r a i l t r a c k

and could cause ser ious damage.

A proper maintenance o f these i tems i s very necessary f o r t he

ra i lway system t o l a s t and provide the requ i red serv ice.

3:5:2:3 Maintenance o f P o r t ra i lway

?here are m y wys inwfiibh the l i f e o f p o r t r a i l t racks may be

lengthened, which w i t h freedom from accident due t o t r a c k

defects i s the main o b j e c t i v e o f e f f i c i e n t maintenance. R a i l

t racks a re made o f s tee l , t he re fo re i t i s n o t s u r p r i s i n g t h a t

corr'bsion i s the most important danger t o ra i lway system i n

the ports. For the r e p a i r and prevent ion o f cor ros ion r e f e r

t o Sect ion 4:3 which d e a l t w i t h the maintenance o f On-shore

s t e e l s t ruc tu res aga ins t corros ion.

A ssuming t h a t t he design and layou t o f the t racks w i t h i t

var ious turnouts, cross-overs, curves and s l i p s i s sound,

perhaps the most important s i n g l e i tem i s good drainage o f

121.

the formation of ballast. Regular attention must be'paid to the

drains and surface water channels, particularly prior to the wet

season. Also the ballast must be kept free from dirts and weeds.

Of almost equal importance, but very largely dependend upon good

drainage - especial ly with clayey or impervious formation, is maintenance of good level, alignment and gauge. Efficiency of heels,

toes and slide chairs of switches, together with the point rods and

level boxes of course essential. It is at the switches where 75% (2)

of any derailment occurs, a system of regular oiling and examination

is part of the normal routine on every port rail system. Switches

constitute the only moving part of the rail system, these require

regular attention. This is very necessary in order to save,costly

, repairs and renewals.

On port rai 1 system the curves in many 'places may be somewhat small

radii and a good deal of wear takes place on both rails and checks,

but regular greasing assist in reducing this wear. Screeching and

grinding, where ever it is heard from traffic passing round a curve

is a sure sign of undue wear.

Resurfacing of worn switches and cross

is now practically universal on main 1

becoming popular on port rail systems.

oxy-ocetylene method of welding, it is

ing rails by welding insitu si

ine railway, and the practice is

The process favoured is the

a1 so less expensive.

With rega rd t o weed k i l l i n g i n t h e p o r t s i t u a t e d i n b u i l t up areas, t h i s

does n o t c o n s t i t u t e a g r e a t problem, b u t where t h e area o f l a n d i s

reserved f o r development, t h e growth of weed and t h e i r d e s t r u c t i o n

presents a s u b j e c t o f some importance. Weeds on r a i l t r acks , if i n

a l a r g e q u a n t i t y a re b e s t dest royed by sp ray ing w i t h chemical weed

n o t i n g r e a t number by t he use o f hoe o r spade. k i l l e r , o r if

The advent o f

d i r t s and mou

immediately.

weeds i n t h e b a l l a s t o f t r a c k s i n d i c a t e

I d , sc reen ing o r renewal o f b a l l a s t shou

t h e presence o f

I d be c a r r i e d o u t

Plate 3:5:3 Maintenance of rail in progress at apapa quays.

. 3.6 Transit sheds, warehouses and container depots.

Most a r t i c l e s of commerce are affected by the exposure

to climatic conditions. The protection from weather for

goods deposited on dock quays i s provided in most cases

by the t r ans i t sheds and warehouses.

Transit shed as the name applies i s used to s tore goods for

a short period of time. Usually immediately a f t e r discharge

of good and also shortly before export.

Warehouse are used to s tore cargo for an indefinate period of

time.

3.6.1 Transit Sheds

Transit sheds are constructed by the quay or berth sides.

General Cargo berth are almost universally provided with

t r a n s i t shed, the purpose of which i s to provide temporary

accommodation for good discharged from vessels which are

awai t i ng clearance through custom or conveyance to the i r

destination by r a i l or raod or to a warehouse for storage.

Also they are used for goods to be loaded into ready vessels.

I t i s accepted in principle tha t t r a n s i t sheds are not

warehouses and should not be used as such. .

The Port Authority has stringent rules involving lenth charge

of goods not cleared by the owner within certain period.

3.6.2 Warehouses

Adequate warehousing accommodation within easy access to the

waterside is an essential adjunct of a modern port. Warehouse

is being required for an almost infinite variety of goods,

example general cargo, tobacco, wool, grain, timber, meat and

perishable foodstuff and sugar are a few which a port may be

expected to accommodate for short or long period of time.

Many of these cargos require special facilities, such as grain

silos and cold store while items like timber are usually stacked

in an open area.

Warehousing faci 1 i ties are of great advantage to consignee who

may not wish to receive into there own premises any or all of

their consignment at the time goods are discharged from ship.

Warehousing is one of the avenue in which the Port Authority

drives its revenue.

The materials use in the construction of docks warehouses and

sheds in Nigeria are concrete,steel sections and blockwork.

The roofing is usually of asbestos. The failure of these

structures are usually caused by corrosion and few cases

settlement: General minor damages are a1 so encountered.

The maintenance of these structures wi 1 1 involve a1 1 the

measures of. protection and repair of corrosion for on-shore

structure as discussed in steel maintenance.

I t will also be necessary to clean regularly.

( A ) Plate 3:6:1 Damage warehouse a t t i n can Island

( B ) P l a t e 3:6:1 Damage warehouse a t t i n can I s l a n d

3;6. 4 Conta iner Depots

C o n t a i n e r i s a t i o n i s now the modern system o f sh i pp ing cargos.

A l l p o r t s a re now equipped w i t h a c o n t a i n e r b e r t h and a

c o n t a i n e r t e rm ina l .

The c o n t a i n e r t e rm ina l a re u s u a l l y a l a r g e open area o f

space which i s used f o r s t a c k i n g c o n t a i n e r a w a i t i n g c lea rance

o r expo r t .

The t e r m i n a l s a re equipped w i t h c o n t a i n e r handing equipment

which i n themselves a re a l s o ve r y heavy. The p o r t s a r e designed

f o r 24 hours opera t ion , t h e r e f o r p a r t o f the i n f r a s t r u c t u r e

here i s t he l i g h t i n g equipments.

The floor slabs are a l l of precast concrete units. a

The fai lure of the -terminal are usually minor crackings which are

easily amended.

The biggest problem concerning failure in terminals i s settlement of

Renovation of such settled terminals require removing the precast

concrete unit and r e f i l l to level, compact and replace the concrete

units. Such settlement has been observed a t Nigerian Port Authority

, .container terminal l i l l y pond Ijora.

Plate3:6:2&Damaged container Depot a t Ijora.

7

P l a t e 3 6:2p1 ' Damaged c o n t a i n e r d e p o t a t I j o r a ,

P l a t e 3 : 6 : 2 c S e t t l e m e n t a t c o n t a i n e r t e r m i n a l L I l l y pond I j o r a .

!;a I ti .; I CHAPTER FOUR

MAINTENANCE MANAGEMENT

4.1 General

The result of maintenance policy may be thought of as a series of cost streams through time. One stream is of direct

maintenance cost, another is of performances cost and penalties

in terms of operating performance and down time. Whilst the

third is of breakdown or failure cost. The first point to be

made is that the relation between expenditure,now on maintenance

and expected future cost for these streams are uncertian.

Similar quantification of relation between preventive and corrective

maintenance considering civil engineering infrastructure, for

instanc,e breakwaters, emphasis should be laid on corrective

maintenance than preventive maintenance.

On the demand side for civil structures, uncertainity of future

usefullife depend on two factors: the first if future life as a

port structure for ship berthing or cargo handling and storage.

The second factor is the use to which these structures may be

put possibly after modification when it is no longer refuired

for port use.

Although there is an increased level of maintenance in the

Nigerian Ports Authority, the level is still very low compared

to the maintenance needs,

There i s an absence o f maintenance management. There i s no proper

maintenance programme, and maintenance p o l i c y . Maintenance are c a r r i e d

o u t pu re l y i n an a c l hoc manner.

Usual l y u n t i 11 complete d e t e r i o r a t i o n has taken p lace before maintenance

are emberked. I n some cases a ser ious damage has occured t h a t r e p a i r

o f t he s t r u c t u r e becomes impossible o r the c o s t t h a t w i l l be i nvo l ved w i l l

n o t be j u s t i f i e d .

The N iger ian Ports A u t h o r i t y Management should p rope r l y fund the

maintenance department. I t i s on l y w i t h adequate funding t h a t a proper

maintenance cou ld be e f f e c t i v e . A very important aspect o f maintenance

regu la r inspect ions are no t c a r r i e d out. Most ly the c i v i l engineer ing

department gets the in fo rmat ion o f de te ro ra t i on o r damage o f a s t r u c t u r e

. from i t s users, sometime, p r i v a t e tenants. I n most cases these tenants

r e p o r t o f d e t e o r i o r a t i o n when i t has become c r i t i c a l t h a t they cou ld n o t

use it. The users u s u a l l y d o n ' t want t o s top h i s operat ion u n t i l they

cannot do otherwise. The co-operat ion o f the tenants and p o r t users i s ,

very v i t a l f o r e f f e c t i v e maintenance.

I n t h i s N iger ian Ports A u t h o r i t y a f a u l t f o r d e t e r i o r a t i o n cou ld be

discovered, b u t the major problem comes from funding. The request f o r

fund has t o go through a very long beauracra t ic cycles, sometimes n o t

approved o r when approved a l o t o f t ime may have been l o s t t h a t the

est imate approved becomes n o t enough t o c a r r y ou t the work.

This occurs due t o the i n f l a t i o n r a t e o r more damage t o the

s t r u c t u r e . Al though t h e management agrees i n p r i n c i p l e about

the i n t e n s i t y and need t o remedy the problem, they s t i l l view

i t as waste o f fund and d o n ' t b e l i e v e i n i t s i

*,

A l l a long the harbours o f N i g e r i a P o r t ~ u t h o r i t y iyou f i n d damaged

c i v i l engineer ing i n f r a s t r u c t u r e s , i .e. s t e e l s t r u c t u r e s which

need r e p a i r s and are n o t at tended t o u n t i l i t i s co l lapsed.

The o n l y a1 t e r n a t i v e i s t o cons t ruc t new one which a t present l e v e l

i s very c a p i t a l i n tens i ve .

be s e t up, t h i s

The unce r ta in t y

the cos t o f the

maintenance po l

I t should be no

the maintenance

The present s e t up do n o t p rov ide t h e much needed maintenance requ i red .

The author suggest t h a t an autonomous maintenance department should

department w i l l be respons ib le f o r a l l maintenance.

i n the va lue o f the n a i r a makes i t d i f f i c u l t t o p r o j e c t ,

maintenance o f s t r u c t u r e f o r one year. The new

i c y a l lows f o r conteneous revaluatuon o f the programme.

t e d t h a t cos t i s t he s i n g l e most impor tan t f a c t o r i n

o f i n f r a s t r u c t u r e s . No mat te r how good a maintenance

programme looks, i t w i l l s t i l l amount no th ing w i t h o u t proper funding.

I t i s d ishear ten ing t o mention t h a t i t became impossib le t o a c t u a l l y

know the amount o f money spent on the maintenance o f ' the c i v i l

engineer ing i n f r a s t r u c t u r e s i n t he N i g e r i a por ts .

There i s no c l e a r maintenance management and c o s t i n g t o be ab le t o

determine e x a c t l y the cos ts o f maintenance. Dur ing the course o f

t h i s study I asked one o f the c h i e f P o r t Engineers (an o f f i c e r

' respons ib le f o r a l l c i v i l engineer ing mat te rs a t the p o r t s ) how

much does he spend y e a r l y on maintenance? He r e p l i e d me i n a proverb

by say ing " t o determine the amount spent on the maintenance o f c i v i l

eng ineer ing s t r u c t u r e s i s j u s t 1 i ke being asked t o separate ' g a r r i '

and sand which have been mixed together" . I n simple word he means

i t i s impossible. A l l t he people asked gave me the same answer.

The chief port engineer went on to lament that 15 years ago, my

inquiry could have been answered immediately but not now.

, At the moment there are different channel of providing fund for

maintenance, the Headquarters, port administrators and also the

chief port engineer himself from his small imprest. The costing

department are not provided with a1 1 informations for their records.

A1 l buildings and civil engineering jobs are also combined and carried

out together.

The following pages will discuss proper maintenance policy for the

Nigerian Ports Authority, in which the commercial ised Port Authority

will benefit.

Supply

Maintenance Policy

Fig. 4:l Factors involved in maintenance

-

Demand

Use

Life

t t Hens to be

Maintained Civil .'. L r

Useful perfor- mance

Life availabi- l i ty

efficiency C

Potential Perfo- - rmance Life availabi-

1 i ty efficiency

4

4:2 I nspec t i on as an aspect of p o r t maintenance.

The f i r s t s tep t o an e f f e c t i v e maintenance management i s a

proper i nspec t i on programme. One o f t he g rea tes t advantage

of i nspec t i on i s sometimes i n a j e t t y s t r u c t u r e underwater,

i f funds are n o t a v a i l a b l e f o r immediate r e h a b i l i t a t i o n ,

b e r t h i n g o f sh ips a t t he p lace cou ld be l i m i t e d u n t i l f u l l

r e h a b i l i t a t i o n cou ld be taken. Without such in fo rmat ion from

inspec t i on the s t r u c t u r e cou ld be t o t a l l y damaged and even

e f f e c t the adjacent s t ruc tu res .

I nspec t i on i s a systematic c o l l e c t i o n data f o r engineer ing

ana l ys i s by v i s u a l , photographic, non-des t ruc t i ve t e s t (NDT)

o r o t h e r means employing t o o l s and techniques s u i t e d t o t he

s t r u c t u r e and environment. I t i s w e l l es tab l i shed t h a t i n the

opera t ion o f any equipment o r f a c i l i t y a planned and me t i cu lous l y

c a r r i e d o u t maintenance programs i s c o s t e f f e c t i v e because, i t

r e s u l t i n s i g n i f i c a n t l ong term savings and increased ope ra t i ona l

a v a i l a b i l i t y . R i s ing cos ts associated w i t h maintenance o f

complex f a c i l i t i e s demand t h a t t he maintenance money be spent

c a r e f u l l y t o r e a l i s e the p o t e n t i a l l ong term savings and

increased opera t iona l a v a i l a b i l i t y .

Any good i nspec t i on can prov ide the f o l lowing in format ions.

i V e r i f y t he i n t e r g r i t y o f t he s t r u c t u r e .

i i Determine the necess i ty f o r r e p o r t o r more d e t a i l e d

inspec t ion .

ii i Determine the scope o f r e p a i r

i v Al low the prepara t ion o f d e t a i l e d r e p a i r s p e c i f i c a t i o n .

A more comprehensive long term inspec t i on programme lead t o

development o f planned maintenance schedule and p r e d i c t i o n of

i n c i p i e n t f a i l u r e s . I n i nspec t i on i t should be noted t h a t most

s e n s i t i v e and vu lnerab le pa r t s o f the s t r u c t u r e are f i r s t subjected

through inspect ion . Such areas inc lude areas o f h igh s t ress

concent ra t ion areas vu lnerab le t o damage from opera t ion a l so

- Seaf 1 oor and scour p r o t e c t i o n prov ided

- S t r u c t u r a l r e p a i r s

- Areas o f d i f f i c u l t cons t ruc t i on w i t h the r i s n of i n f e r i o r

workmenship a

- Construct ion j o i n t s sub jec t t o

o f s t ress

- Steel p l a t e s and b u i l t i n i tern

equipment.

reversa l o r l a rge v a r i a t i o n

IS forming f i x i n g s f o r ope ra t i o

The i n i t i a l i nspec t i on plans depends on an assesment o f these f a c t o r s

b u t as soon as i nspec t i on s t a r t s the r e s u l t s generate a s t r u c t u r e

c o n d i t i o n records which can be c a r e f u l l y analysed t o determine the

need f o r any changes i n the plan. I t i s s t r o n g l y emphasised t h a t the

i nspec t i on process i s s imply data gather ing. The u t i l i t y o f the data

depends upon the subsequent engineer ing ana lys is , and employment o f the

data.

To ensure t h a t proper data i s obta ined . i n a form which can be u t i l i z e d

engineers and managers should p a r t i c i p a t e i n i nspec t i on p lann ing and

technology se lec t i on . Engineers should p a r t i c i p a t e because they w i 11

be doing the analys is , managers because they w i l l use the data f o r a

f a c i l i t y h i s t o r y o r r e p a i r s p e c i f i c a t i o n .

The major types o f i nspec t i on are invo lved the atmostpheric i nspec t i on

which i s above water and the underwater i nspec t i on which i s below water

surfac,e.

4:2:1 Atmospheric i nspec t i on

Atmospheric i nspec t i on i s appl i c a b l e t o open s t r u c t u r e s e ighe r

on-shore o r o f f -shore. Thesa s t r u c t u r e s i nc lude p lat forms quay

decks and o the r open f a c i l i t i e s i n t he atmospheric/dry zone o f

concrete p lat forms, t h e i nspec t i on methods inc lude.

1. Visual : This i s by f a r the most important type o f concrete i nspec t i on

f o r assessing s t r u c t u r a l cond i t i ons and i d e n t i f y i n g s igns o f

d e t e r i r o a t i o n . I n t e r p r e t a t i o n o f v i s u a l data i s g r e a t l y helped by '

a knowledge o f the p l a t f o r m design and cons t ruc t i on and o f concrete

.as a ma te r i a l . Adequate l i g h t i n g i s an e s s e n t i a l and a minimum

measured i 11 i umi nance o f 150 1 ux i s recommended (41) .

Surface c l e a r i n g of the concrete w i l l be requ i red i n areas subjected

t o the h igher standard inspec t ion . Defects and suspect defects are

normal ly photographed.

2. Coring: Concrete cores of small diameter are usually taken

t o preven't cutting prestressing tendons and buried services.

There i s ,usua l ly no problem with small cores taken for chemical

t e s t . Core holes are normally sealed with epoxy mortar.

3. Schmidt Hammer: This i s used for comparative e

surface hardness and sometimes can prove usefu

l imits of damage or substandard concrete.

valuation of

1 in assessing the

4. Drilling: These are sometimes use to estimate chloride and

moisture content b u t are less rel iable than cores

5. Covermeter: The l a t e s t model i s of these instrument are rel iable

b u t very heavy reinforcements, sometimes in double layers often

encountered in association presstressing tendons and heavy s teel

cable ducts may make i t d i f f i c u l t to determine the location and

depth of individual rebars.

6 . Pundit: Even with access limited to one side of a member i t i s

possible t o use ultrasonic pulse velocity measurement to estimate

concrete strength and t o provide an indication crack depths.

7. Crack W i d t h Measurement

The surface width of cracks may be measured optically b u t t h i s

i s sometimes d j f f i c u l t where cracks seepage w i t h subsequent s i l t

sealing in whole or parts. However i t i s not usually necessary

to know the absolute crack width very accurately.

If the crack is wide enough to have possible structural significance,

it is much more important to know if the width is changing

between successive inspections. In obtaining the information, the

Demec gauge is a most useful tool (42).

Where cracks are to be monitored in locations of difficult access the

use of vibrating wire strain gauges with remote monitaring should

be considered in place of Demec points.

8. Electro - Potential Mapping and Concrete Resistivity Measurement These techniques can now be quickly and effectively used with the

development of the lightweight battery operated recording instruments

which will store a days work of 'several readings.

Interpretaion of the result is often not straight forward requiring

experience.

- - Generally the result can be interpreted to give an indication of the

liklihood of corrosion but do not in themselves provide a measure

of corrosion rate nor therefore a definite indication of whether any

indicated corrosion is structural ly significant (4).

9. Gamma - Ray Backscatter

This has been used on land to assess the extent of concrete materials

- depredation, where this is believed to have occured froni other

evidence of all tools of inspectio? available it is largely visual 3

inspection that may be of significance. Most of these tools could

- o n l y be a v a i l a b l e w i t h consul tants . Although t h e technique o f

p o t e n t i a l mapping may i n d i c a t e rebar co r ros ion be fore the re a re

v i s u a l s igns o f t he r e s u l t . The o the r methods o f sampling and

N.D.T can a s s i s t i n determin ing t h e ex ten t and na ture o f t he

de fec t .

4:2:2 Underwater i nspec t i on

The above water p o r t i o n o f a s t r u c t u r e presents w e l l understood

i nspec t i on work d e f i n i t i ' on and maintenance problem. The p o r t i o n

below water i s a very d i f f e r e n t case. The i 'ncent ive f o r t h e

development o f underwater i nspec t i on technology came from the

o f f s h o r e o i l i n d u s t r i e s where s t r u c t u r e o f r a d i c a l design are

exposed t o extreme environmental cond i t ions . The i nspec t i on

techno1 ogy developed o f f s h o r e has widespread appl i c a t i o n t o p e ~ r t

f a c i l i t i e s and o the r c i v i l s t ruc tu res . With maintenance and r e p a i r

cos ts f o r ag ing s t r u c t u r e s r i s i n g and technoiogy a v a i l a b l e t o

gather data f o r engineer ing eva lua t i on and conf i rmat ion , t he re i s

no longer a reason f o r t h e o u t o f s i g h t o u t o f mind a t t i t u d e t h a t

has p r e v a i l e d i n t he i nspec t i on o f underwater c i v i l works use o f

o f f s h o r e underwater i nspec t i on technology i n t he apparent ly more

benigh environment o f harbours and i n l a n d waters, has g rea t appeal.

The appeal steams from t h e r e a l i s a t i o n t h a t underwater s t r u c t u r e s

can be inspected e f f e c t i v e l y and t h a t a good i nspec t i on programm

can r e s u l t i n b e t t e r maintenance.

There i s not a d i r ec t corre la t ion between the offshore and inland

environment. Differences ranges from materials wood i s not used offshore

due t o environment conditions l i ke turbedity of water.

There a re ongoing e f f o r t s t o adapt offshore techniques ' t o the condition

found in the ports and harbours, and to develop technology t h a t works

where techniques are not adequate. More comprehensive programmes have

greater potential f o r long range saving. Saving accrue from developing

a f a c i l i t y his tory t o predict maintenance requirement and from developing

substantive information fo r feedback into future designs. The choice of

the appropriate inspection technology i s extremely important. Techniques

appropriate fo r one type of s t ruc ture or ,material may be t o t a l l y unsuited

fo r another. Applying the wrong technology can be wasteful and f ru s t r a t i ng ,

and can lead t o the erroneous conclusion t ha t underwater inspection i s not

workable.

I t i s cost e f fec t ive fo r Port Authorities learning the underwater

inspection business t o have an expert assistance in se lect ing the inspecting

technology and means of development. To ensure ob jec t iv i ty the underwater

contractor or consul t an t who a s s i s t the Port Authorities should normal l y

be proscribed from bidding the inspected works.

Under Water Inspect ion Methods

I n the recent pas t underwater inspect ion was 1 im i ted t o v i s u a l o r

t o r c h inspect ion by d ivers . Often the d i ve rs were n o t t r a i n e d t o

recognise o r descr ibe cond i t i ons found i n terms meaningful t o the

engineer. The engineers was dependent upon inadequate o r incomplete

repo r t s and.was unable t o evaluate completely the s t r u c t u r e and

w r i t e comple te , repa i rs s p e c i f i c a t i o n . The a b i l i t y t o conduct more

meaningful i nspec t i on was increased by the employment o f underwater

t e l e v i s i o n and has been f u r t h e r enhanced by non-destruct ive t e s t

procedure s p e c i f i c a l l y adapted f o r underwater s t ruc tu res .

a. Cleaning

A1 1 inspect ion techniques r e q u i r e some c lean ing of the surface

t o ob ta in accurate observat ion and measurements. The degree o f

c lean ing requ i red i s dependent upon the inspect ing technique

t o be used i h e s t r u c t u r a l ma te r i a l and the type o f sur face

coverage. With harbours becoming cleaner, there i s an increase

i n the q u a n t i t y o f marine l i f e which must be removed form p o r t

f a c i l i t y s t r u c t u r e before c leaning. If the s t r u c t u r e i s h e a v i l y

encrusted w i t h marine growth o r o the r sur face cover c lean ing

i n p repara t ion f o r the i nspec t i on may be t ime consuming than the

i nspec t i on i t s e l f .

Among the techniques used f o r c l ean ing sur faces f o r i nspec t i on are

powered and hand brushes scrapers and gr inders , Needle guns and h igh b

ii

pressure water o r s l u r r y j e t s may aTso be used. Needle guns a re n o t

recommended as they tend t o peel t he sur face o f heat t r e a t e d s t e e l

sur faces and t o remove sound m a t e r i a l s on wooden and concrete sur faces.

High pressure water j e t s pressures can be v a r i e d t o s u i t t he surface

being cleaned and the thoroughness o f the c lean ing can be t a i l o r e d t o

t he i nspec t i on process being used.

b. V isual I nspec t i on

Visual i nspec t i on are p a r t i c u l a r l y good as i n i t i a l i nspec t i on t o l o c a t e

areas o f i n t e r e s t f o r l a t e r d e t a i l e d i nspec t i on o r t e s t i n g .

A major shortcoming o f v i s u a l i nspec t i on i s t h a t r e p o r t s a re based

on observa t ion t h a t a re n e c e s s a r i l y ' l a c k i n g i n bo th p r e c i s i o n and

completeness. No two observers o f the same defec t , no mat te r how

w e l l t r a i n e d wil-1 make the same,repor t . I t i s d i f f c u l t f o r d i v e r s t o

make accurate measurements i n water w i t h t he low v i s i b i l i t y . Usua l l y

d i v e r s a re requ i red t o use f l a s h l i g h t s t o increase h i s v i s i b i l i t y .

To i nsu re t h a t a v i s u a l i nspec t i on i s as complete as poss ib le , t he

i nspec t i on i s conducted i n a h i g h l y organised manner. I t should n o t

be conducted i n a haphazard o r random manner. The d i v e r should be

- prov ided w i t h as much i n fo rma t i on as poss ib le about t he s t r u c t u r e he

i s t o i nspec t and c o n d i t i o n he can expect t o f ind . The d i v e r should

r e p o r t h i s obse rva t i on i n a s tandard pre-ar rdned fo rmat and

vocabulary.

c. Photographic Recording

Photographic r e c o r d i n g means t h e use o f chemical o r e l e c t r o n i c

imaging techniques t o produce a permanent v i s u a l records o r f i l m

o r tape. Permanent records, a re o b j e c t i v e q u a n t i f i a b l e da ta t o

documents t h e c o n d i t i o n o f t h e s t r u c t u r e t o f a c i l i t a t e e v a l u a t i o n

o f i t s cu r re r i t c o n d i t i o n s by qua1 i f i e d people and t o p rov ide a

r e c o r d f o r de te rmin ing o f t he r a t e o f d e t e r i o r a t i o n . S t i l l

photography, v ideo-photograping o r combinat ion may be used.

i . S t i 11 Photography

S t i l l Photography may be used i n genera l survey o r i n d e t a i l e d

. i n s p e c t i o n of a p a r t i c u l a r i tem. Because o f t h e a d d i t i o n a l

i n f o rma t i on produced c o l o u r photography i s u s u a l l y p r e f e r a b l e

t o b l a c k and wh i te . Both p r i n t s and s l i d e s a re use fu l , which

ever chosen depend upon t h e use t o be made o f t he record .

The u t i l i t y o f s t i l l photography i n water w i t h l a r g e amount o f

suspended p a r t i c u l a t e mattermmay be l i m i t e d . The u l t i m a t e

usefu lness o f t h e i n s p e c t i o n photography i n ana l ys i ng t h e 1

c o n d i t i o n o f t h e s t r u c t u r e i s dependent upon t h e s k i l l of t h e

photographer. I t i s c o s t e f f e c t i v e t o p l an underwater i n s p e c t i o n

photography c a r e f u l l y and t o employ d i v e r - photographer who a r e

exper ienced i n making photographic inspec t ions .

i i . Stereo - Photography

Stereo - Photography, where in overlapping images are taken with

identical lenses with a known separation, produces a three

dimension ef fec t and allows accurate three dimensional measurement

to be made by photogrammetry. The accuracy of the techniques i s

highly dependent on the equipment. I t s condition and the s k i l l of

the photographer. The Primary advantage of the stereo photography

and photogrammetry are that they reduce lengthy, re lat ively inaccurate

diver measurements and increase the amount of information obtained

over other techniques for making precision measurement of conditions

vis ible from the surface of the structural component.

In harbour inspection stereo - photography and photogrammetary are

valuable primarily in making small area inspection to examine

conditions which have been located by general survey and require P t

close examination. These techniques have the disadvantage of

requiring special equipment for viewing a complex computer based

technique for complete analysis.

The turbid waters found in most harbours present a problem for both

s t i l l and stereo - photography that can be eliminated by the use of

a cleanwater box between the camera and the object being photographed.

This technique i s especial ly useful in stereo -photography where

c l a r i t y i s important for photogrammetry.

iii. Videophotographx

The most common t o o l used f o r underwater i n s p e c t i o n i s v i deo

camera, mon i t o r and recorder . The Video cammera p resen ts

r e a l t ime i n fo rma t i on t o opera to rs and t e c h n i c a l people

underwater and a l l ows them t o d i r e c t t he a c q u i s a t i o n of

p a r t i c u l a r data and a vary t he conduct o f the i n s p e c t i o n i n

response t o emerging i n fo rma t i ons . The v ideo tape p rov ide

a va luab le permanent r eco rd when p r o p e r l y marked and nar ra ted .

Both c o l o u r and b l a c k and w h i t e t e l e v i s i o n a re used f o r under-

water i nspec t i on . One o f t h e ma jo r b e n e f i t s o f v i deo i n s p e c t i o n

i s found i n t he m o n i t o r i n g and da te reco rd ing . The r e a l t i m e

m o n i t o r i n g of t he i n s p e c t i o n a l l ows emphasis t o be d i r e c t e d

towards areas o f i n t e r e s t as they a r e d iscovered by t h e

general survey. Recording o f t he i n s p e c t i o n a l l ows t he m a t e r i a l

t o be p layed f o r d e t a i l e d s tudy o r f o r the t he i n f o r m a t i o n o f

s e n i o r managers. The VHS r e c o r d i n g format has proven s a t i sfac-

t o r y f o r a l l types o f i n s p e c t i o n se rv i ces (37 ) .

The v ideo system should always i n c l u d e equipment f o r making

t he tape w i t h supplementary i n fo rma t i on and a t i m e r which

p r i n t s t ime and da te i n f o r m a t i o n on the screen.

The va lue o f a v ideotape i s inc reased g r e a t l y by an accura te

n a r r a t i v e . The purpose o f t h e n a r r a t i v e i s t o o r i e n t t he

viewer and described i n general terms what he i s seeing. As i n

v i s u a l inspect ion a standard vocabulary should be used.

While reference should be made t o s p e c i f i c cond i t ions noted, the

inspectors should at tempt on l y t o descr ibe the condi- t ion and n o t

preerr~pt the engineers work of diagnosing the cond i t i on . I n a l l

types o f i nspec t i on where the techniques i s p r i m a r i l y v i sua l a s i z e

reference i s extremely useful.. Such a reference i s p a r t i c u l a r l y use fu l

when a permanent.record i s t o be kept f o r determinat ion o f c o n d i t i o n

changes w i t h time.

D. Non - Des t ruc t i ve Tes t ing (NDT)

Inspect ion o f the sur face t o a f i n e r degree than can be obta ined

w i t h e i t h e r the human eye o r sur face imaging o r i nspec t i on o f the

i n t e r i o r of the s t r u c t u r e requ i res the use o f non-destruct ive t e s t i n g

techniques.

A general p r i n c i p l e i n underwater work t h a t app l i es p a r t i c u l a r l y

t o underwater NDT i s t h a t as much equipment and ana lys is as poss ib le

should be done on the surface. The d i v e r has enough t o do t o operate

the inst rument which c o l l e c t t he data. For b e t t e r i nspec t i on r e s u l t

when the d i v e r i s s imply and inst rument f o r feeding date t o a NDT

techn ic ian on the surface.

. . 1. Radiography

Radiography is one of the most common NDT techniques used on

the surface f~rdetectkon~~f interior volumetic flaws. Radiographic

techniques have have had limited use underwater. The primary use

has been in dry 'hyperberic welding of pipe1 ines. There has been

some radiographic inspection of flat platesrStructures using

gramma emitting isotopes, but the technique is not generally

empl oyed .

: I

~ a d i o ~ r a ~ h ~ has the advantage of having I radioactive material

at the inspection site and of requiring hibhly trained and well

qualified surface and diver technicians.

2. Magnetic Particle Inspection

magnetic Particle Inspection can be used to detect discontinuities

in the surface of ferromagnetic const~uction both on the surface

and in water in underwater inspection the ferromagnetic particles ;?

are coated and suspended in dye," usually water based which becomes

flourescent under. UItra- violet light usually with wavelength in

the 3000 toL)4000 amstrom range (37)

A magnetic field is induced by application of a permanent magnet,

electromagnet or current production making the test piece the

conductor magnet with pulls of 15 to 150 pounds and low voltage

(10V) and high current (1000A) are used (37). Surface discountin- uities which show up after the establishment of a field may be

photographed or 'videotaped to obtain a permanent record. Magnetic

particles inspection provides an easy and accurate means of detecting

surface and limited surface and fau l t s .

With the technology in use a crack detection ra te of 0.99 can be

expected (37 ) . The major drawback of the technique in harbour

structures i s that i t i s applicable only to s teel or other

ferromagnetic materi a1 s . . .

3. Eddy Current and Surface Potential Testing

Eddy current tes t ing also provide a method of detecting cracks

and other surface or near surface flaws such as p i t s and voids.

This type of testing can be used on ferromagnetic materials

which have a conductive surface such as reinforced concrete.

I t i s frequently used underwater because of the extreme sens ib i l i ty

of the probe to stand off distance surface i r regular i ty and

surface condition.

Surface potential measurement particularly when combined with

automatic logging provide a method of assesing the corrosion

potential on the surface of a reinforced concrete surface.

E. Ul trasonics

Ul trasonic determination of materi a1 thickness.and 1 ocation of

sub surface discontinuities and flaw i s the most commonly used

underwater NDT technique.

The technique is used routinely on steel and concrete structures

with excellent results. The best system require the diver to handle

only a small probe which transmit the reading to surface logging

equipment and allows him to have an hand free for maintaining his

position. Difficul t'ies encountered on steel surfaces with extensive

corrosion giving fa1 se reading have been overcome by focusing.

The means by which the human eye, still cameras, or TV cameras are

transported from the platform or a support vessel through the sea

surface to depth of 150m or more may be divided into three groups

(42)

i. Divers

These are the most universal and flexible means of undertaking

visual inspection using the eyes of the diver or manipulating

a sti 1 1 or TV camera.

Possibly the best method available for Coastal and Ocean

engineers to experience the problems and difficulties of working

underwater is to become a diver.

The' professional engineer and experienced as a diver can be

a key element in the design and construction of Coastal and

offshore structures.

Introducing the engineer directly into the Ocean and Coastal

waters through diving allows him an opportunity to gain an

excel lent understanding of the physical process that govern

underwater desi gn.

By describing the capabilities and function of the diving engineer.

It is hoped that this wi 1 1 encourage Port engineers to consider b

the advantage of training engineers as divers. The diving engineer

has two basic functions in the design and construction of underwater

structure (i ) Reconnaissance and (i i ) Construction inspection. Basic

first hand knowledge of a project site characteristic is obtained

through diving reconnaissance. Assurance of quality underwater

construction work is obtained through diving inspection.

i i Manned Submers i bl e

These are self propelled free swimming vessels manned by pilot/

observer, they may include diver lockout facilities. They provide

the best means of inspection by the human eye because the observer

can be experienced engineer operating in a dry atmospheric envi-

ronment, externally mounted sti 11 or TV cameras can be used.

i i i Unmanned Submersibles

These have been called remotely controlled submersibles or vehicle

(RCS or RCV). They are used extensively for routine underwater'

inspection by TV cameras and photography.

Record P

There is little point in making the inspection if a record is not

kept. It must be in a form that it can be used for engineering

analysis, provide an input for management decision, and to be

understood by the new relative to record preparation are repeated

here for emphasis

i ) Data accumulat ion should be done tops ide .

i i ) Records 'should be made i n r e a l t i ine.

i i i ) W r i t t e n reco rd should be i n a te rmino logy agreed on be fo re

the i nspec t i on .

i v ) Photographs, v ideotapes and NDT records should be marked

w i t h the s t r u c t u r e and l o c a t i o n the t ime and t he i d e n t i f i c a t i o n

o f t he recorder .

v Video tapes should be nar ra ted .

The exac t fo rmat and con ten t of t h e i n s p e c t i o n r e p o r t i s t he

p r e r o g a t i v e o f the o r g a n i s a t i o n r e q u i r i n g t he i nspec t i on . The P o r t a . A u t h o r i t y who knows what they want and t he underwater c o n t r a c t o r

who knows what he can do should work toge ther t o develop t he

r e p o r t formats.

4: 3 Maintenance Management Pol i c y

The problem w i t h maintenance o f c i v i l eng ineer ing i n f r a s t r u c t u r e s

i s t h e l a c k o f adequate maintenance management t h a t w i l l emphasis

how t h e human element among p o r t personnel, can be organised and

channe l led so as t o inc rease t h e a c t u a l l e v e l o f maintenance

management e f f o r t a p p l i e d t o p o r t f a c i l i t i e s , and p rov ide f o r t h e

c o n t r o l and r e d u c t i o n o f p o r t maintenance c o s t over a l ong term.

To achieve these o b j e c t i v e management must know how p o r t maintenance

ought t o f u n c t i o n and how t o measure t h e r e s u l t a c t u a l l y achieved.

Here we a re goi'ng t o i l l u s t r a t e some ways i n which t h e maintenance

process cou ld be a p p l i e d t o t he N ige r i an Po r t s A u t h o r i t y C i v i l

. eng ineer ing f a c i l i t i e s .

In order to obtain an effective maintenance and control maintenance '

2 L

cost, the management should reconsider its concepts about the

maintenance team.

The management do not usually consider the vital importance of the

maintenance people and their efforts. No one notice them until some

facility failure has accured and must be dealt with, then they are

criticized for delays and cost of the repair process. Morale drops,

the quality of their efforts deteriorate and eventually the really

important.work must be contracted out. The supervisors or foremen

are under severe pressure from their unionized crew members to

perform only as well as the least effective members of the maintenance

work force. The foreman commonly takes refuge in his office where

plenty of paper work can be invented to make his day look worthwhile.

Mean while maintenance jobs drags on and on at a leisure pace that

suites everyone except the customer and management.

This whole scene is repeated for so many years that the situation

is considered normal maintenance costs, in man-hour and materi a1

have increased dramatically in the last 10 years.

The concept of maintenance programme, means the formation of a

plan to reach. specific goals this concept embodying a maintenance

programme is designed to be applied to port organisation.

Maintenance programme however always need t h e a t t e n t i o n and invo lvement

o f a l l t h e d i v i s i o n s a t severa l l e v e l s w i t h i n t he p o r i o r g a n i s a t i o n

s t r u c t u r e . A good and implemented maintenance programme w i l l b e n e f i t

P o r t Management group i n t h e f o l l o w i n g ways:

a ) Execut ive - Execut ive management w i 11 have b e t t e r y a r d s t i c k w i t h

which t o i h s u r e t h e o v e r a l l performance o f maintenance management

and supervis ion.,

b ) Finance - The f i nance o f f i c e r w i l l be ab le t o b e t t e r p r e d i c t

maintenance expend i tu re and budget ing f o r c o s t a l l o c a t i o n purposes. b

c ) Operat ions - The opera t ions management can assess damages

r e p a i r s i t u a t i o n and can i n f l u e n c e maintenance s t ra tegy .

d) .Engineer ing - The eng ineer ing group w i 11 have access t o improve

i n fo rma t i on f o r p l ann ing purposes and f o r i n t e g r a t i o n of smal l

c a p i t a l i s e d work i n t o back log o f r e p a i r works.

c ) Real Es ta te - The r e a l e s t a t e opera t ions w i l l be ab le t o w r i t e

c l e a r e r leases as rega rd t h e maintenance o f p o r t p roper ty .

f ) P lann ing - The p o r t p l ann ing group can asses t h e impact o f '

maintenance ope ra t i on and c o s t on p r o j e c t e d new i n s t a l l a t i o n s ,

improved f a c i l i t i e s w i l l a t t r a c t more i n t e r e s t from p o t e n t i a l

customers.

g ) Tenants - The p resen t tenan ts w i J l have a c l e a r channel t o

o b t a i n maintenance work.

A maintenance programme starts with the looking into the present

setup in which the present adhoc system of maintenance are carried 8

out. A proper X-ray into the system and staffing. A developed

maintenance management should result in reduction of cost and improved

efficiency in the following ways,

1) Planning the work so as to remove possib

before they have a chance to happen, and

probabi 1 i ty of job completed on time.

1 ays le obstructions and de

thereby enhancing the

2 ) Scheduling the crews activities to maximize job site time and to

. help the first line supervisor contribute to efficient work

execution.

3) Recording what happens, with the work, so that the crews and C

maintenance management can profit, from the port experience of

themselves and others.

4) Instal 1 ing a preventive maintenance programme that assures

regular checkups of equipment a facility and also highlight high . cost,situation, for intensive treatment.

I.

5) P rov id ing maintenance feed back i n fo rma t i on t o a1 1 ow

maintenance management t o budget t h e i r resources and t o

f o l l o w an e x p l i c i t maintenance s t ra tegy .

4:3:1 Elements o f Maintenance Programme

1) Maintenance Organ isa t ion S t ruc tu re and S t u f f i n g

This new s t r u c t u r e i s developed from the present s e t up o f

c i v i l engineer ing department i n t he ' A u t h o r i t y ' . The new

s t r u c t u r e i s w e l l de f i ned i n terms o f du t i es and r e s p o n s i b i l i t i e s

expected from the i n d i v i d u a l s . The problem o f a c c o u n t a b i l i t y

i s w e l l taken care o f i n t h i s new s e t up.

The maintenance manager w i 11 be under the D i r e c t o r Engineering.

The p lann ing department should make proper economic and

f i n a n c i a l ana lys is , a l t e r n a t i v e g i v i n g the lowest cos ts i n

terms o f present day va lue would be the optimum economic

s o l u t i o n . This however does n o t mean t h a t t he so

the lowest c o s t i n terms o f present day va lue wou

s o l u t i o n t o f o l l ow .

l u t i o n g i v i n g

I d be the

Factors such as a v a i l a b i l i t y o f funds, the s t r u c t u r a l cond i t i on ,

ope ra t i ona l e f f i c i e n c y , s a f e t y and p o l l u t i o n aspect and socio-

economic cons ide ra t i on would i n f l u e n c e the f i n a l dec is ion .

The steps f o l l o w i n the whole ana l ys i s i s shown i n the f l o w

c h a r t below.

A

tce Cost Useful ; .Obtain .Input 4

I

Djscounts Rate probability users benefits time span analysis

A , . T

I 'v I Economic Analysis * I

I Optimum Alternative I

Fi'nancial Analysis

I P r i o r i t y Rating I

0 Up date

Review Constrain

No

As Update 0 Update

Pro ject Execution - 1

0 Data base

/-/input Output

0 Decision

Fig 4:3 Economic/Financial Analysi Flowchart

It would appear obvious that all inspection and maintenance efforts

should be systematically recorded, also data must be easily retrievable

for references and use for planning. The work planning and scheduling

section under assistant manager, this group handles customers contracts,

manages the work order system, schedule and maintenance and record

jobs progress. This group acts as a buffer between the varying wor k

demand and the work execution crews.

A work execution section under assistant managers (maintenance) for

electrician, mechanical works and the other for construction works.

This section takes the planned work and pursues high quality work

finished on time and within estimated cost.

A maintenance warehouse section under a warehouse assistant manager

for maintaining a proper inventory of materials, a store catalog,

for expediting special requirements, for obtaining common items from

local vendors, and for providing reports to accounts payable.

A preventive maintenance section with personnel for developing and

implementing the preventive maintenance programme.

A personnel administration section under assistant manager warehouse

and administration handle personal records, overtime list payroll and

safety.

- 2.. The work order and manpower scheduling system

This daily reckons the best use of maintenance man hour tools

and repair materials to minimize work result.

The system uses ground rules to put important revenue producing

jobs first. The system combines the idea that, work follows from

the objective and a maintenance strategy reflection the needs for

operations, engineering and finance, and every job, identified and

specified before hand is actually planned in terms of labour,

materials and equipment required.

The ground rules for maintenance planning and scheduling are:

i) All maintenance and small constructions works should always be

handled through a formal ized maintenance work order system.

Except for real emergencies, all jobs are planned before hand.

The work order is used to input maintenance date into the

computer

i i ) The originators of the work set the priority for scheduling the

work.

. i ii) The maintenance workforce is scheduled so as to ensure a full

days work for each tradesman.

iv) The daily work scheduling process follows a specific timetable

so as to key planning efforts together.

v ) The completed work information from planning and schedul ing

is the basis for reporting about maintenance effectiveness.

3 . The role of maintenance as it affects other port divisions and

tenants.

Maintenance performs as a services to the custom and to other

division within the port. While the maintenance group may be

internally efficient, others set the working environment that

determines how effective maintenance will be. The following points

are of importance.

i) The tenants, through their lease arrangement, need to know

about the k,inds of maintenance for which they will be

responsible and further how to get action on their problems.

ii) The responsibilities for maintenance budget should rest with

those that want and order service from maintenance.

ii i ) The work plans from engineering to maintenance should comprise

adequate drawings and bills of materials so that work orders

can be planned and schedule to obtain the best result at

least cost.

iv) The finance division should retain the purchasing activities

so that cash flow for materials is controlled and to separate Y

the money for items from theik receipts and storage.

V) The follow up on work order written form damage report should

be the function of the operations group.

These and other grounds rules defining the role of maintenance should

be set down in writing. This will reduce frustration and loss

of time.

4. Maintenance M a t e r i a l s , I n v e n t o r y and Warehouse Operat ions

A warehouse o r s t o r e s ope ra t i ons produces se rv i ces t o t h e ba lance

o f t h e maintenance o r g a n i s a t i o n demand f o r m a t e r i a l s and

The i n t e g r a t i o n o f warehouse o p e r a t i o n

concept as f o l l o w s .

s hou I d a r

t h a t

i s e f rom

i ) A warehouse c a t a l o g must be deve 1 oped p r i m a r i

t he needs o f maintenance c ra f t smen supe rv i so r s and

spare p a r t s .

management

y serves

p lanners .

The i tems i n f o r m a t i o n shou ld b q o r g a n i s e d t o l o c a t e and

c l a s s i f y t h e m a t e r i a l s and spare p a r t s and show q u a n t i t i e s

and hand.

i i ) A c l a s s i f i c a t i o n o f m a t e r i a l s and spare p a r t s must be made

accord ing t o whether each i t e m i s an insurance s tock o r

expendable i tem.

i i i ) The r e c e i v i n g and i s s u i n g procedure shou ld be d e t a i l e d i n t o

t h e work o rde r system t o a l l o w c o m p i l a t i o n o f m a t e r i a l s usage

record.

i v ) The system o f i n v e n t o r y c o n t r o l must be based on t h e economics

o f tu rnover , r e o r d e r p o i n t s and q u a l i t y , t ime and s e t a g a i n s t

t h e random s tockou t .

4. M a i n t e n a n c e - ~ a c i l i t i e s , ShopandEqu ipment .

The a v a i l a b l e maintenance f a c i l i t i e s , equipment and t o o l s must f i t

t h e work t o be done. These p o i n t s concern f a c i l i t i e s and equipment

r e l a t e d t o maintenance e f f i c i e n c y .

i i )

i i i )

i v )

6.

D i s t r i b u t e t h e workforce meet ing p laces t o match t h e area of

workload. Dur ing t he o r d i n a r y work ing day cons iderab le t ime

i s l o s t t r a v e l l i n g t o and f r o .

Prov ide a business - o r i e n t e d atmosphere f o r t he p l ann ing

super in tendent and h i s subord inates.

The warehouse should be a c losed area w i t h s u i t a b l e p r o v i s i o n

f o r s h e l v i n g and p e l l e t i n g t h e s t o r e d i tems.

An annual i n s p e c t i o n programme, a r i s i n g f rom p reven t i ve

maintenance should be made o f s t r u c t u r e s t o ensure con t inued -

s e r v i c e a b i l i t y .

P reven t i ve Maintenance

Preven t i ve maintenance uses t h e b ra ins , exper ience and e f f o r t s o f

a l l t h e maintenance people t o a v o i d as n e a r l y as poss ib le , t h e need

t o r e a c t i v a t e r e p a i r s . By d e f i n i t i o n a l l maintenance i n i t i a t e d and

scheduled independent ly o f a c t u a l equipment f a i 1 ure, d i scarnabl e need

f o r r e p a i r s , personnel s a f e t y o r appearance.

Co r rec t i ve maintenance i n c l u d e a l l o t h e r r e p a i r s where maintenance

i s performed as a consequence o f equipment f a i l u r e and work i s done

because o f observed f a c i l i t i e s d e t e r i o r a t i o n .

Preventage maintenance should cover p o r t p r o p e r t i e s , such as: water

*meters , fender p i l e s , ca thod i c anodes fence and gates, f i r e alarms,

b r idges .

The development o f p revent ive maintenance invo lves : -

i

i i )

i i i )

i v )

v

v i )

7.

C o r r e l a t i o n o f equipment c h a r a c t e r i s t i c s by serv ice l oca t i on ,

capaci ty , type spare p a r t s e t c .

Development o f the prevent ive maintenance work orders and

c.orresponding jobs i n s t r u c t i o n s sheets f o r each c lass o f

equipment,

Creat ion and d i s t r i b u t i o n of an equipment note book f o r t he

maintenance planners and eng ineer ing d i v i s i o n .

Arrangement o f t he prevent ive maintenance annual schedule.

I n d o c t r i n a t i o n of maintenance superv is ion and work force

concerning prevent ive maintenance.

I n t e g r a t i o n of t he prevent ive maintenance data and cos ts

i n t o t he maintenance performance r e p o r t i n g system.

Work Execut ion Rules and Superv is ion

To accomplish work and o b t a i n an acceptable l e v e l o f r e s u l t , t he

craftsmen and superv isors must a c t u a l l y be a t t h e i r scheduled j o b

s i t e s a major p o r t i o n o f the working day. The two problems i nvo l ved

here a re the c o n s i s t e n t a p p l i c a t i o n of maintenance work r u l e s t h a t

promotes f u l l j o b s i t e s attendance by the work crew. And t h a t the

d a i l y work schedule a re indeed workable w i t h i n the c a p a b i l i t i e s of

the var ious crews.

The o v e r a l l purpose i s t o ach ieve jobs completed as planned every

work ing day. Maintenance supe rv i s i on c o n t r o l s t he work f o r c e

department i n two ways: General and S p e c i f i c .

General : each member o f maintenance supe rv i s i on exerc ises s u r v i 11 ance

o f a l l maintenance personnel where ever encountered i n t he Po r t . A1 1

have a c o l l e c t i v e r e s p o n s i b i l i t y t o observe t h a t conduct f o l l o w s

maintenance work r u l e s and

S p e c i f i c ; each maintenance supe rv i so r i s accountable f o r t he day

a c t i v i t i e s , f o r t h e p r o d u c t i v i t y o f t h e work r e s u l t s ob ta i ned by

ass igned crew.

1 ong

h i s

T i g h t a d m i n i s t r a t i o n f o t he day ' s p l a n n i n g and da i 1y work schedu 1 i n g

a c t i v i t i e s make reasonable sense and i f t h e superv iso rs app l y t h e

work r u l e f i r m l y and f a i r l y across t h e whole maintenance work f o r ce .

8. Maintenance by Outs ide Cont rac to rs

Outs ide c o n t r a c t o r s can f u l f i l l a v e r y va luab le r o l e i n t h e execu t i on (

of some maintenance work. I n d e f i n i t i o n t h e k i n d s a n d q u a l i t i e s o f

work t o be performed by o u t s i d e con t rac to r s . These i tems a re

impor tan t :

i ) Con t rac t o u t f o r s p e c i a l i z e d s k i l l s o r l a r g e amounts o f man

power f o r s h o r t per iod . Use c o n t r a c t o r s t o match o n l y t he peak

i n t he work l oad and h i g h l y s p e c i a l i s e d works.

i i ) Con t rac t w i l l be a t t h e h i g h e s t l e v e l o f the.maintenance

o rgan i sa t i on .

i i i ) Complete drawings and bills of materials must be available for

supervisory control, before hand. As nearly as possible avoid

any "Surprise" costs or delay once they are started.

;&v) A knowledgeable supervisor should be assigned, from inside the i:P l .a

, 1- maintenance organization to physically make sure that the work

called for is actually completed as planned.

9 . Maintenance Data and the Computer.

The Nigerian Ports Authority should incorporate the use of computer

to aid maintenance management, to generate better work control decision.

Some data that need handling include.

i) The maintenance information data base comprising a wide range of

updated equipment labour and price data.

i i) . The equipment notebook for correlation of equipment numbers

and nomenclature.

i i i ) Development and printing of the warehouse catalog.

iv) Automatic inventory control of warehouse stock and issuance

of purchase requisition.

v) Warehouse transaction and expediting information.

vi) The work order backlog and timing

vii) Mobile equipment usage against work order

vi i i) Actual man-hour used per work order

i x) Preventive maintenance work order schedules and instruction sheets.

x) Equipment history of repair file.

xi ) Maintenance cost and performance report. ".

4:3:2 The use of Maintenance data for cost control

Once the foregoing aspects of daily and weekly maintenance

efforts are underway, the maintenance manager can use computer

generated reports to contr.01 the results that his organisation

is achieving.

The maintenance manager needs to generally review maintenance,

to determine how well or not the organisation is coping with

the on going work load, what are the significant work and cost

trends that reflect the ports function system.

The use of data for effective cost control will include:

1. Reporting on the Present State of Affairs:

To find out how well the organisation is coping with the work

load on weekly and monthly basis. The manager tries to find

out

i How much of the schedule preventive maintenance actually got 3

done as scheduled? . ii) What was the percent of man-hour devoted to preventive

maintenance to the total hour worked?

i i i ) What is the present work backlog by crafts and by general areas

. throughout the port?

iv) What kinds and sizes of work orders are stalled waiting for

materials? Engineering design? Contractor available?

Approval ?

168 c . V ) What k inds o f emergency p r i o r i t y jobs a r e handled? Where? and

how much d i d t hey c o s t ?

v i ) What l e v e l o f compliance d i d t h e supe rv i so r ach ieve a g a i n s t d a i l y

work schedule?

v i i ) What k inds o f work o rders were t h e most overspent?

v i i i ) What percentage o f man hour were charged t o s tand ing work

o rde r and t o non p roduc t i ve numbers?

i x ) What k inds o f work o rders a r e 30 days o r more i n t he back log?

x ) What percentage o f man hour worked were used on c o n s t r u c t i o n

p r o j e c t s ?

x i ) What i tems o f mob i le equipment a re i n t h e shop f o r ove rhau l i ng?

2. Repor t ing Work and Cost Trends

Th is i n f o r m a t i o n i s shown i n mos t l y cos t s r e p o r t s form work o rde rs

man hours and cos t s da ta f rom the data base. The work and c o s t

in fo rmat ion a r e con ta ined i n these k inds o f maintenance r e p o r t s :

i ) Equipments maintenance cos t s r e p o r t s . Th i s month ly r e p o r t

summarizes t he maintenance c o s t per f a c i l i t y o r i t e m o f p o r t

equipment.

: . i i ) Summary o f equipment cos ts . Th is month ly r e p o r t t abu la tes t h e

c o s t of maintenance i tems o f equipments, as t he work ing yea r

un fo lds .

i i i ) F a c i l i t i e s cos t s by tenant . Th is month ly r e p o r t summarizes t h e

p o r t maintenance cos t s i n c u r r e d by each tenants as t he work ing

year un fo lds .

i v )

v )

v i )

3.

Summary o f charges t o s tand ing work order . This monthly r e p o r t

presents t he cos ts charged t o bo th p r o d u c t i v i t y and non produc t ive

s tanding work orders.

Summary o f work orders cos ts by p r i o r i t y . This monthly r e p o r t

summarizes the maintenance cos ts i n c u r r e d by operat ions and

segregates the cos ts t o t a l s according t o t he needs andt iming

o f t he j o b demanded.

Comparisons o f ac tua l vs est imated cost . This monthly r e p o r t

presents a comparison o f ac tua l and est imated jobs cos ts

ranked by order o f t he c o s t magnitude.

Cost Contro l Ac t i on by the Maintenance Manager

The maintenance manager w i l l c o n t r o l ~ c o s t s by:

i

i i )

i i i )

Evo lv ing a formal monthly c o s t rev iew programme.

Help ing the prevent ive maintenance engineers t o so lve h igh c o s t

s i t u a t i o n .

Working f rom the work backlog data t o assume t h a t t h i s

maintenance s t r a t e g y i s being at tended t o .

Reviewing w i t h o t h e r p o r t s d i v i s i o n s and tenants t h e i r

maintenance cos ts .

A Format Cost Review Programme

Each month the maintenance manager needs t o b r i n g h i s e n t i r e

superv isory group together , i n c l u d i n g the prevent ive maintenance

engineer and the warehouse o f f i c e r s t o rev iew the present cos ts

l e v e l s and work o rder r e s u l t s so t h a t c o n s t r u c t i v e ideas are generated

a-nd discussed t o l ead t o b e t t e r c o n t r o l jobs and hence costs.

The e n t i r e superv isory s t a f f becomes cos t conscious and a p u b l i c

commitment i s made t o focus on work areas t h a t seen out o f c o n t r o l .

5. So lu t i on t o High Cost Maintenance Problems

The maintenance manager and the prevent ive maintenance engineer should

evolves a l i s t o f the ten most maintenance s i t u a t i o n s i n the po r t .

They should l ook f o r so lu t i ons t o these problems by rev iewing the

equipment opera t ing cond i t ions as a way t o reduce damage and wear

and t e a r t h a t c o s t considerably. Improving the ma te r ia l s on component,

w i t h i n the equipment t o p rov ide a longer serv ice because o f reduced

cor ros ion and b e t t e r care. Working, w i t h the maintenance superv isors,

t o change and improve maintenance work method so t h a t longer l a s t i n g

r e s u l t s are obtained.

6. Working w i t h Backlog In fo rmat ion

The p lanning managers t racks and char ts the backlog t o assess the

volume o f outstanding work w i t h an eye toward developing s h o r t term

plans, by weeks and months ahead, t o concentrate on s p e c i f i c p o r t s

areas where p a r t i c u l a r c r a f t backlogs are h igh matching the plans fo r

r e n t a l mobi le equipment w i t h the whole volume o f work i n view.

And a l so s a t i s f y i n g s p e c i f i c tenants by co-ord ina t ing w i t h the tenant

own work load.

7. Other d i v i s i o n s and Tenant's maintenance Costs

The computerized maintenance cos t i n fo rma t ion w i 11 a1 low the

maintenance manager an oppor tun i t y t o v i s i t on q u a r t e r l y basis, w i t h

each tenant t o rev iew p a r t i c u l a r maintenance costs, t o determine what

can be done t o c o n t r o l and t o reduce costs.

Review with the other port divisions maintenance costs charge to

their accounts with an eye towards improving operating methods to

reduce maintenance charges.

These cost control review processes seek to augment the personal

observation of port management with summarized information that can

pinpoint locations and ways to reduce cost. This is an ongoing duty

of maintenance management and truly one of the significant contributions

of management to a well-run port.

Final ly when the maintenance management has been ful ly implemented

the next aspect to consider will be the personnel training. A good

training programme should be put forward for the personnel. This

will enable them td keep to date with the latest techniques in the

fie1.d of maintenance engineering. Apart from improving, the ski 1 1

training has a capacity of motivation, of the personnel.

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