Hoek Y Bray Rock Slopes Engineering

8/3/2019 Hoek Y Bray Rock Slopes Engineering

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12.1

Chapter 12 Stabilization and protection measures

Introduction

Expenditure of funds for slope stabilization programs is oftenled because unstable slopes can rarely be tolerated on

h Ighways, and because weathering of the rock tends to causedeterioration of slopes with time. This chapter i bes aternative stabil ization methods and the conditions in whichthey can be used. Design of the stabilization work is carriedout by the methods described in Chapters 7 through 10 for theappropriate type of slope failure; references to these design

methods are included with each of the stabilization procedures.Note that each design method is particular to the type of slope

fa i lu r e , i . e . p la n a r , w e d g e , c i r c u la r o r to p p l in g , a n d i t i sessential that the type and cause of failure be identified.

The first step In planning a stabilization program is to iden-tify potentially hazardous slopes which usually requires accu-rate observations of slope stability conditions and the main-tenance of records over a considerable time period. These re-cords, which can be kept by maintenance personnel, should con-tain the following information.

L o c a t i o n o f s l o p e .

Weather conditions, particularly during 24 hours pre-ceding fai lure.

of failed material and height of fal I.

Time taken to clear rock and stabilize slope.

Belays to traffic and damage to highway and vehicles.

Stabilization work carried out with time and costs.

Warning received of failure from prior falls, or move-ment monitoring instruments (see Chapter

These reports should be supplemented with photographs to recordchanges in conditions of the slope and the progress of stabili-zation work. Photographs in stereo pair are particularly usefulfor planning stabilization work. They can be taken with a regu-lar 35 mm camera by taking two photographs from positions whichare separated by a distance equal to about 2 to 5 percent ofthe distance of the camera from the slope. For more detailedwork, or oblique aerial photogrammetry can be usedfrom which contour maps and cross-sections can be drawn up.This information is usually required in making detailed sta-bility studies and calculation of excavation volumes. High al-t i tude aer ia l photographs rare ly prov ide in formation suff i -ciently detailed for rock slope engineering.

By relating these records to the geological data contained onstability assessment discussed previously (seeure 1 .6 ) . information will soon be developed on the most haz-ardous areas and the consequences of the failure. This can thenbe used to schedule stabilization work, keeping in mind that

slopes that have already failed are I ikely to be more stablethan similar slopes that have not yet failed.

The selection of an appropriate I ization method dependsnot only on the technical feasibility, but a costs and the


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12 . 4

S u r f a c e d r a i n t o c o l l e c t r u n - o f f b e f o r e

i t can en te r the top o f open tens i on

c r a c k s . T h i s d r a i n b e w e l l

graded and must be kept c lear

P o t e n t i a l t e n s i o n c r a c k

Slope surface immediate ly behind

crest should be graded

C o l l e c t o r d r a i n - /

d r a i n a g e w e l l 7

Vertical pumped .

H o r i z o n t a l h o l e t o

b as e o f t e ns i on

P o t e n t i a l

H o r i z o n t a l h o l e t o

d r a i n p o t e n t i a l

f a i l u r e s u r f a c e

Potent

tension crack

Subsurface

d r a i n

increase drainage ff iciency

of sub -sur face ga l l e ry .

g a l l e r y

F i gure 12 . 1 : Slope drainage and depressuri rat ion measures.


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12 . 6

. . .

. . . .

. .

. .. .

. . .

h a n g t r immed

r o c k s c a l e d

t r i m m e d

on new

F i g u r e 1 2 . 2 : S c a l i n g a n d t r i m m i n g .

E x c a v a t e d m a t e r i a l

s u r f a c e

face

F i g u r e 1 2 . 3 : U n l o a d i n g


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12.7

out, for hlgh slopes, by men working from ropes or on cablesusponded platforms and, for lower slopes, fromcranes or booms. If crane Is used the basket mustbe tied to the slope to prevent It from away from the

face. and are slow operations because movlngon the face Is slow and only hand-held equlpment can be

used.

Careful of a l l should be

out to the rock to be removed and ensure that the new

face Is stable. For example, In Flgure hand ofthe rock I I form an overhang that I I have to be

A l l t h a t I s o u t

should be of strength to break the rock and notd amag e t he sl op e. T h l s r e q u l r e s t h e o f

carefully al Igned, closely spaced holes and the use ofcharges . See Chapter for Is of control led

procedures.

The frequency of Ing vary between 2 and 20 years anddepends upon the rate at the rock weathers and thef of such factors as root growth and traff Ic

use.

The trimming operation shown in has created aunlfon slope face benches. It is the recommendation

o f th e th a t In te r me d ia te b e n c h e s o n s lo p e fa c e sshould be avolded because they rarely have width to actas effective rock areas; it is preferable to form aw i d e a t t h e t o e o f m e s l o pe . T he a ct ua l w id th o f benches Is usually less than the design width due to loss ofrock along the crest and to remove rock at the toe of

the upper cut. Furthermore, small rock fal ls mat doI ate on the benches, further reduce their dth and eventu-ally form which project I ing rocks outwards tot h e Cleaning of accumulated rock falls on benches

Is rarely carried out because of the danger of working onhigh rock faces, and Is Impossible if a substantial fall cutsthe access on to the bench.

Intermediate benches be effective if they have widths ofat least ft. as shown in Figure 12.3, where the crest of

the slope has been raved. The required dth of the bench

should be checked on the ditch deslgn chartwhich shows the required wldth and depth for the slopesions. If the width is lnsufflclent, a berm or shouldbe constructed along the outside edge to trap rol I Ing rock,but only If the crest stable.

Unloading

Where I lure of the slope Is rather than

fa l I s o f ln d iv ld u a l b lo c k s o f r o c k , s ta b 1 c a n b eachieved by (unloading) the crest to reduce the

f o r c e 1 2 . 3 ) . The volume of material to beremoved Is determined by methods describedearlier the manual. The procedure for a back analysis Isa s The position of the surface Is estimatedf r o m t h e o f t h e c r a c k , t h e g e o l o g y , a n d

d r l l l l n g .


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12.8

T h e t y p e o f s l o p e f a i l u r e a n d t h e c a u s e s o f f a i l u r e a r e

I d e n t i f i e d a n d a s t a b i l i t y a n a l y s i s i s c a r r i e d o u t u s i n g af a c t o r o f s a f e t y o f 1 . O t o d e t e r m i n e t h e r o c k s t r e n g t hparameters. Then, using the same strength parameters andgroundwate r leve l , a d d i t i o n a l a n a l y s e s a r e c a r r i e d o u t t odeterml ne how much mater 1 al must be un I oaded to i ncrease thefac to r o f sa fe ty to an accep tab le leve l . S tab i l i ty o f a l l fou r types of s lope fa i lures p lanar, wedge, c i rcu lar and

depend upon the slope height, which is reduced by unloading.

Si i t may be necessary to un load as much as of thefa i lure in order to stab1 i t , th ls work wi I I have to bedone with earth-moving equipment except in the case of minor

ides. For this equipment to have sufficient working space,the cu t I I have to be a t leas t 20 f t . w ide and p re fe rab ly3 0 to 4 0 f t . w id e . I f b las t ing is requ i red , v ib ra t ions shou ldbe kept to a minimum by reducing the charge weight per delayas much as (see Chapter 11 because large vibrationsmay be suff ic ient to cause the slope to fa i I . I f the s lopei s mo v in g d u r i n g e xca va t i o n , movement systems( C h a p t e r s h o u l d b e s e t u p t o p r o v i d e a w a r n i n g o f d e t e r i o r a t i n g s t a b i l i t y c o n d i t i o n s . T h i s w i I I e n s u r e , i f fal lure were to occur, that men and equipment wi I I have tlmeto evacuate the slope.

Resloplng

Th is s tab i l i za t ion method is app l ied in s im i la r cond i t ions to

the unloading method when overall slope fai lure is occurring.I f appears doubtfu l that un loading wi l l ach ieve long-term

I because extensive movement and rock breakage haveoccurred, then It would be necessary to excavate the slope ata flatter slope (see Figure 12.4). Much thesame de sign a n d e xcava t i o n meth o d s a nd p re ca ut i o n s areapp l icab le in bo th un load ing and res lop ing . The new slopeshould have a face angle that produces a satisfactory factoro f s a f e t y b a s e d o n t h e s t r e n q t h a n d q r o u n d w a t e r v a l u e sd e t e r m i n e d f r o m b a c k a n a l y s i s : I n d e s i g n i n g t h e c u td imen sion s, su f f i c i e n t sp a ce mu s t b e l e f t a t t h e to e o f t h eslope for equipment to operate which means that a triangularshaped excavation (in section) cannot be made. Intermediate

benches should not be incorporated in the slope design unlessa significant width, say 30 ft., can be accommodated.

In both un loading and reslop ing, addi t ional pract ica l matters

to consider are property ownership of the land along the crest

a n d a v a i l a b l e a r e a s f o r t h e d i s p o s a l o f t h e e x c a v a t e dmate r ia l . Long hau Is may be expens ive , al though there isa lwa ys th e p o ss ib i l i t y t h a t t h e ma te r i a l co u ld b e u se d fo r

e lsewhere at some cost savings over quarr ied materla l .F ina l ly, contro l led b last ing should be used to min imize rockdamage.

II REINFORCEMENT AND SUPPORT STABILIZATION METHODS

The fo l lowing is a descr ip t ion o f s tab1 methods in

which the forces resisting fal lure are increased by instal Iingei ther re in forcement or support .

Re 1 nf cons sts of i n s t a l I i n g b o l t s o r cab I es

across the f a i l u r e s u r f a c e t o ncrease ts s tr en gt h,

whi support consists o f i ns ta l I in g dowels, Is,

o r but t resses at the t o e o f the f a i l u r e .

Usua l ly , re i n fo rce me n t I s u se d fo r smal ler fa i lures where

the forces ar e n o t g r ea t a n d t h e t e ns i on th a t c a n b eappl ied to the anchors Is suff ic ient to produce a sign i f icanti n c r e a s e i n t h e f a c t o r o f s a f e t y . H o w e v e r , v e r y h i g h


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12.9

N e w s l o p e a n g l e

i g i n a l s l o p e a n g l e

E x c a v a t e d m a t e r i a l

F a i l u r e s u r f a c e

M i n i m u m o p e r a t i n g w i d t h

F i g u r e 1 2 . 4 : R e s l o p i n g .

( a ) U n t e n s i o n e d b o l t s . T e n s i o n e d a n c h o r s i n s t a l l

t h r o u g h l o o s e b l o c k .

ed

F i g u r e 1 2 . 5 : R o c k b o l t i n s t a l l a t i o n s .


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12.11

strength the failure surface. Methods installingand tensioning bolts are discussed below:

Tensioned bolts are made tensile strength steel and

have threads on the exposed end for a bearing plate and nut.The d i f ferent types of anchors that can be used Inc ludemechanical expansion shells, cement grout and epoxy grout.

Both mechanlcal and epoxy grouts allow tensioning to beout soon otter installation which is an advantage If

a c c e s s t o t h e s i t e I s d i f f i c u l t . Mechanlcal anchors are

usually some form of wedge which is expanded by turning ordriving the bolt. Two component epoxy resins are packaged inplastic tubes and are mixed by rapidly the bolt. By

using resin with different settling times, the anchor setin a few minutes and the remainder will set after the bolt hasbeen tens

Cement or epoxy grout is usual I used in soft rock where

mechanlcal anchors could slip, and grout Is used torall high capacity, permanent anchors. Cement grout shouldhave a agent added, and hi-early strength cements houl d not be us ed be ca us e i t i s b r i t t l e a nd s ome t i me s

contains reagents that accelerate corrosion. The length ofthe anchor zone Is us ng the assumption that theshear stress Is along the periphery ofthe ho l e . the re qu i re d bond l e ng th I scalculated from the following equatlon:

where T is the applied tenslon and d is the hole diameter.

The working rock/grout interface shear strengths fordesign varies about 50 psi in weak rock to 200 psi Instrong rock. In general, the working bond strength is about

to of the compressive strength the rock.I t i s a l s o f o u n d t h a t t h e s t e e l / g r o u t s h e a r s t r e n g t h i susually greater than the rock/grout shear strength.

Te ns l on i ng i s c a r r i e d ou t by pu l l i ng on the bo l t w i th ahydraulic jack to a load of about 50 percent of the yieldand l o c k i n g i n t e n s l o n b y t i g h t e n i n g t h e n u t .Alternatively, a torque wrench can be used tor tensioning. butt h i s i s l i k e l y t o b e l e s s r e l i a b l e t h a n u s i n g a

jack.

After al I bolts should be fully grouted to provide

protection and to In the tension. Mechanicalanchors should only be considered temporary means of malntalnlng tension because the and creepin the highly stressed rock around the anchor can lead to loss

of load. The bolt manufacturers i n s t a l l a t i o nprocedure should be carefully followed.

Cables

Cables can be used to relntorce rock slopes in a similar

manner to rlgld bolts as above. However, cableshave a greater strength than rlgld bolts of the same diameter

and so can be used to large rock


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12.12

corrosion

protected cable anchor

De ta i

d

masses For example, a 1 inch diameter rigid boltmay have a working tensile strength of 25,000 lb. while a

inch, 7-wire strand cable has strength of 40,000 lb. I f greater strengths are required, then bundles of as many as 50cables can be used. A further advantage of cables is thattheir f lexibil i ty al lows them to be coiled which facil i tatesinstallation where space is limited and rigid bars could onlybe used i f they were coupled together in shor t lengths .Cables can be either tensioned or untensioned in identicalapplications to rigid bolts and the same design methods (seeChapter are applicable.

Because of the high tension on cables, cement grout anchorageis usually used which must be allowed to set for several daysbefore tensioning. Be fo r e in s ta l la t io n b e g in s , th e h o leshould be tested to see if fractures have been intersectedthrough which grout cou Id flow out of the hole and preventfu I I embedment. I f the hole cannot be f i l led wi th water ,then it should be fi I led with a low slump grout to seal thefractures and re -dr i l led when the cement is par t ia l ly se t

The anchor is formed by pumping grout down a grout I ine sot h a t t h e h o l e i s f i l l e d f r o m t h e b o t t o m , w i t hattention being paid to ensuring that the head is fully pro-tected corrosion with grout and anti-corrosion agents.W h e n t h e g r o u t h a s s e t , t h e t e n s i o n i s a p p l i e d w i t h ahydraulic jack using load/deformation monitoring proceduresas spec i f ied by the Post Tens ionary Ins t i tu te (298) . The

applied tension is maintained by securing the cables withtapered wedges which are pushed into tapered holes in theb ea ri ng pl at e. W h en t he g ro u t h as s et , t he t en s io n isis appl ied with a hydraul ic jack . The applied tension ismaintained by securing it at the collar with tapered wedgesby using a bearing block with a tapered hole through whichth e c ab le pa ss es . T h e pa i r of ta pe r ed w e dg e s a r e fi t tedaround the cable and pushed into the tapered hole so thatthey grip the cable and hold the tension. The of thebear ing p la te should be suff ic ient to d is tr ibute the loadwithout fracturing the rock under the plate.

Dowels

Dowels are lengths of bars, or blocks of relnforcedconcrete, Installed at the toe of unstable blocksto prov lde support (see 12 .6 ) .Thls support Is provlded by the shear and bend strength ofthe s tee l , or the shear strength of the relnforcedconcrete. The number of dowel s to support a block Iscalculated as follows (see sketch).

where: W of blocko f p la n e

plane anglesupport provlded by dowel

The methods In Chapter 7 can be used to de-velop Include the effects of and water

pressure.

D o w e l i n s t a l l a t i o n t os u p p o r t s l i d i n g b l o c k .


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12.13

The support provlded by the dowel Is the lesser of Itsbendlng strength or Its shear strength, as follows:

Shear,

where: strength of steelof Inert a of bar

radius of bararm of load on dowel

shear strength of steel.

These show the support Is Increased byI ng the of the bar, and that the bendlng Isdecreased by havlng the block load the dowel above the embed-ment polnt In the rock. T h ls th e Imp o r ta n c e o f

the dowel the face of the block.

If extra shear Is then a number of dowels

can be placed In a group Is then encased In concretepoured the rock face.

dowels are Inch to Inch

bar. fo r th ls d o w e l c a n b e d r lhand-held The of Is between 1 and 2

f t. dependlng on the of the rock. The dowel Is fu l lygrouted Into the hole and a concrete cap can be cast over thedowel to protect It and make sure the supportIs In contact the rock. I f I t I s n o t t o d r l I Ithe hole at the toe of the block, then the dowel can be bentagalnst the face after

of dowel support (128)and rock slope parameters show that a l-3/8 Inch

bar I hold a block a volume of about 5 to 15 cu.yd.Therefore, should only be used to support smal I, Isola-ted blocks where Ing would not produce permanent I

and boltlng would be more expenslvr. As noted above,stronger dowels can be constructed from blocks of relnforced

concrete.

Buttresses and Walls

Buttresses and retaining walls are usually reinforced concretestructures constructed at the toe of slopes, or beneath over-hanging pieces of rock to provide support and resistance toslidin g (see Figure Concrete buttresses are used tosupport overhangs that a re d i f f icu l t to remove because of access problems, or the danger that more rock higher up theslope may become unstable. The concrete buttress shou I d have

mass and strength to resist the weight of rock andalso be securely tied to the face with reinforcing tie-backsgrouted into holes I led In the rock. The tie-backs I Iensure that the buttress does not It outwards if the forceappl ied by the rock is not co inc ident wi th the ax is of thebuttress.

The required strength of the buttress is the difference betweenthe component of the weight down the failure plane and the


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12.14

b a r d o w e l s

R e i n f o r c e d c o n c r e

F i g u r e D o w e l s t o s u p p o r t s l i d i n g

b l o c k s .

L o o s e b l o c k

b u t t r e s s

t e

f i g u r e S u p p o r t a t t o e o f u n s t a b l e s l o p e s .


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12.19

o f a Free

r o c k f a l l

fr a d i e n t

100

O v e r a l l s l o p e d e g r e e s

F i g u r e D i t c h d e s i g n c h a r t .

SlopeHeight

F i g u r e 1 2 . 1 0 ( b ) : R o c k f a l l s o n s l o p e s .


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12.21

F i g u r e 1 2 . 1 1 : F e n c e t o c a t c h r o l l i n g

r o c k .

F i g u r e 1 2 . 1 2 : W i r e m e s h o n s l o p e t o t r a p f a l l i n g

r o c k .

Photograph courtaay

Railway.

of

F i gu re 1 2 . 13 : R oc k s li d e pr ot e ct i on f e nc e


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12 .23

R o c k s h e d s .

P h o t o g r a p h s c o u r t e s y o f

C a n a d i a n N a t i o n a l R a i l w a y

F i g u r e 1 2 . 1 4 : Rock sheds and tunnels.


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12 . 25

O r i g i n a l s l o p e

d i t c h

s l o p e

F i g u r e 1 2 . 1 5 :

C r o s s - s e c t i o n s h o w i n g r a i l r o a d , h i g h w a y

a n d d i m e n s i o n s o f d i t c h e x c a v a t i o n .

s e t o f f r a c t u r e s

F i g u r e 1 2 . 1 6 :

U n s t a b l e w e d g e f o r m e d b y i n t e r s e c t i n g

f r a c t u r e s .


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12.29

L i m i t f o r

6

L i m i t f o r

4

D is tance b las t feet

Figur e B las t damage cont r o l c ha r t .

Rock

Wal ls

F i g u r e C o m p l e t e d s l o p e w i t h d r i l l i n g

in pr ogr ess fo r d i t ch

excavat ion .

F igur e 12 .19 : D i tch a f te r const r uct ion

o f


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1 2 . 3 0

C ont r ac ts

A t a r g e t t y p e c o n t r a c t w a s u s e d f o r t h i s p r o j e c t t o g i v e t h e

c o n t r a c t o r i n c e n t i v e t o c o n t r o l c o s t s , w h i l e p r o v i d i n g f

b i I i t y i n t h e e v e n t o f c h a n g e d q u a n t i t i e s o r m o r e t r a f f i c i n -

t e r r u p t i o n s t h a n s e t o u t i n t h e c o n t r a c t . E a c h b i d d e r s u p p l i e d

t h e o w n e r w i t h a n O r i g i n a l T a r g e t E s t i m a t e b a s e d u p o n t h e d e -

s i g n va l u e of r o ck t o b e e x c a va t e d, a n d a l u m p s u m p r i c e f o r

access const r uct ion . Th is es t imate w as ad justed upon job com-

p l e t i o n , f o r c h a n g e s i n q u a n t i t i e s o r w o r k t y p e , t o b e c o m e t h e

F i n a l T a r g e t E s t i m a t e . A p e n a l t y c l a u s e f o r o v e r e x c a v a t i o n

beyond the design l ine was also included to encourage the con-t r a c t o r t o r e d u c e o v e r - b r e a k f r o m b l a s t i n g a n d t o e x c a v a t e t h e

m in im um a mo un t o f ro ck . S i n c e p a y m e n t s t o t h e c o n t r a c t o r w e re

b a s e d u p o n a c t u a l c o s t s , e a c h b i d d e r w a s r e q u e s t e d t o s u p p l y

o f r a t e s f o r a n d e q u i p m e n t , a n d t o p r o v i d e b a c k - u p

c a l c u l a t i o n s f o r t h e O r i g i n a l T a r g e t E s t i m a t e .

T h e f e e o r p r o f i t t o t h e c o n t r a c t o r w a s q u o t e d s e p a r a t e l y i n

the t e n d e r a n d c o u l d b e a d j u s t e d t o r e f l e c t t h e d i f f e r e n c e i n

t h e F i n a l a n d O r i g i n a l T a r g e t E s t i m a t e s . T o p r o v i d e a n i n c e n -

t i v e , t h e f e e w a s o n a s l i d i n g s c a l e : i f t h e a c t u a l c o s t o f t h ew o r k w a s g r e a t e r t h a n t h e F in a l T a r g e t E s t i m a t e t h e n t h e f e ep a y a b l e w o u l d b e r e d u c e d b y x p e r c e n t o f t h e d i f f e r e n c e ; i f i tw e r e l e s s t h a n t h e F i n a l T a r g e t E s t i m a t e t h e n t h e f e e w o u l d b e

i n c r e a s e d b y p e r c e n t o f t h e d i f f e r e n c e . B o t h t h e s e p e r c e n -

tages were bid i tems and were 10 percent and 40 percent respec-

t i v e l y .

S e v e r a l c o n t r a c t p r o b l e m s d e v e l o p e d d u r i n g t h e c o u r s e o f t h e

p r o j e c t ; t h e f o l l o w i n g a r e s u g g e s t i o n s o n h o w t h e y m i g h t b e

avo ided .

a) A lunp sum payment was to be made for a I I access con-s t r u c t i o n a n d r o c k e x c a v a t e d o u t s i d e t h e d i t c h d e s i g n

I ines. T h i s m a t t e r w a s d i s c u s s e d a t t h e p r e - b i d s i t em e e t i n g , b u t l a t e r d i s a g r e e m e n t s a r o s e o v e r t h e

t l o n o f r o c k t h a t w a s t o b e p a i d f o r i n t h e l u m p s u m

payment , and tha t w h ich w as to be pa id a t cost . It is

suggested that these two classes of rock be very clear -ly d e f i n e d a n d t h a t r e c o r d s o f p r e - b i d m e e t i n g s b e i n -c l u d e d i n t h e c o n t r a c t .

T r a i n s d e l a y e d w o r k o n 5 0 p e r c e n t o f t h e w o r k i n g d a y s ,

i n t e r r u p t i n g t h e c o o r d i n a t e d r a i l w a y - h i g h w a y c l o s u r e

schedule. P r o d u c t i o n l o s s e s d u e t o d e l a y s s h o u l d b ee s t i m a t e d a n d s p e l l e d o u t i n t h e c o n t r a c t s o t h a t t h ec o n t r a c t o r c a n i n c l u d e t h i s i t e m i n h i s b i d c a l c u l a -

t i o n .

T h e b l d s s h o u l d b e a n a l y z e d t o e n s u r e t h a t t h e c o n -

t r a c t o r i s n o t h i s b i d a n d t h a t h i s

q u o t e d r a t e s a r e o u t - o f - p o c k e t c o s t s a n d d o n o t i n c l u d e

p r o f i t .

T h e c o n t r a c t s h o u l d i n c l u d e a n t o e n s u r e

t h a t t h e c o n t r a c t o r d o e s n o t p r o l o n g t h e j o b f o r w h i c h

he is pa id cost p lus the min imum fee .


31/32


32/32

12 .32

3 0 6 . K . , C O A T E S , O . F . , G Y E N G E , M . A r t i f i c i a l s u p p o r t

o f r o c k s l o p e s . M i n i n g R e s e a r c h C e n t r e , M i n e s B r a n c h ,

O t taw a R esear ch R epor t , R . 228 , 145 p . , 1971 .

3 0 7 . SOWERS, SOWERS, G.F. I n t r o d u c t o ry I m e c h a n

a n d f o u n d a t i o n e n g i n e e r i n g . T h i r d e d i t i o n ,

P u b l i s h i n g C o . I n c . , N e w Y o r k , 5 5 6 p .

3 0 8 . VAN RYSWYK R., T u nn e l re p ai r s. C o n st r uc t i on We s t , p p .

10-l 1, September 1979.

3 0 9 . R IA M A K R ISH N A N , V . , C O YLE, W.V . , FO WLER , L .J . A com-

p a r at i v e e va l u at i o n of f i b r e s h ot c r et e s . S ou th D a ko ta

School of Mines and Technology, Report SDSM-T-CBS 7902,

August 1979.

3 1 0 . T . L . S h o t c r e t e i n h a r d r o c k t u n n e l I i n g . B u l I .

A s s o c . E n g . G e o l . , V o l . I X , N o . 3 , p p . 2 4 1 - 2 6 4 , 1 9 7 2 .

3 1 1 . AMERICAN CONCRETE INSTITUTE. Shotcreting. ACI

5 0 6 , A C I S P - 1 4 , D e t r o i t , 1 9 6 6 .

3 1 2 . RITCHIE, A.M. E v a l u a t i o n o f r o c k f a l I a n d i t s c o n t r o l .

H ighw ay R esear ch B oar d , R ecor d 17 , Wash ington ,

1 3 - 2 8 , 1 9 6 3 .

3 1 3 . FUKUOKA, S. P e r s o n a l

3 1 4. MEARS, A. I. P e r s o n a l

315 . E . , E . T . U n d e r g r o u n d e x c a v a t i o n s i n r o c k .

London, England, 1981.

Hoek Y Bray Rock Slopes Engineering

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