Influence of change in pile diameter at various locations of a pile...

Indian Journal of Geo Marine Sciences

Vol. 46 (06), June 2017, pp. 1198-1209

Influence of change in pile diameter at various locations of a pile group

in a Berthing Structure

P. V. Premalatha*1

, S.Senthil Kumar2 & K.Baskar

3

1Department of Civil Engineering, CARE Group of Institutions, Tiruchirappalli - 620009, Tamil Nadu, India 2Department of Civil Engineering, KSR College of Engineering, Tiruchengode -637211, Tamil Nadu, India

3 Department of Civil Engineering, National Institute of Technology, Tiruchirappalli -620015, Tamil Nadu, India

[ E.Mail: [email protected] ; [email protected] ; [email protected] ]

Received 20 July 2015 ; revised 01 December 2015

Numerical analyses have been performed using the Finite Element software on a single frame pile group of a Marine

berthing structure in sloping ground. A case study from Chennai port trust (India) is taken with the actual soil profile of a marine

environment. Diameter of piles at various locations in a sloping ground has been varied to study its influence on the load

distribution among the piles and lateral load carrying capacity of the pile group. The results showed that increasing the diameter

of piles in the slope crest increases the lateral load carrying capacity of the pile group, whereas increasing the pile diameter on

the down slope redistributes the overall load on the frame. It is concluded that increasing the diameter of rear piles decreases the

deflection of the structure to a large extent. Increasing the diameter of the front and rear piles distributes the load more evenly

among the piles of the berthing structure.

[Key words:Marine structure, Berthing Structure, berthing force, mooring force, pile diameter, tie-rod anchor]

Introduction

Piles of a Marine Berthing structure are subjected

to both axial and lateral loads and are generally

on sloping ground. The load sharing mechanism

among these piles (which are in sloping ground)

is different from the pile group present in a

horizontal ground. Literature from past1-10

gives a

general guidance in predicting the load

distribution among the piles in horizontal

ground.It concludes that the front piles towards

the loading direction carry more loads compared

to the other piles, whereas in sloping ground, the

piles on the slope crest carry the max load

transferred to the structure.

Many researches are being reported on the effect

of tie rods in the behaviour of marine berthing

structure. The various alternative systems for a

marine berthing structure considering a

combination of diaphragm wall and piles in a

marine structure are studied11

. The study revealed

that by marginally increasing the diameter of the

pile the lateral capacity of the pile was increased

rather than providing tie rod anchors.Results from

tie rod force measurements in a Cargo Berth at

Paradeep Port (India)12

and studies on the pullout

capacity of anchors in marine clay for mooring

systems13

gives a general idea on the behaviour

and load transfer mechanism of tie rod anchors.

A two dimensional (2D) finite – element analyses,

to study undrained soil deformation around piles

displaced laterally through soil is carried out14

.

The load-transfer p-δ curves produced were found

to be applicable for design during passive loading

but not for active lateral loading of pile groups.

The p-δ curves characterize the local soil – shear

deformation around the pile, whereas p-y curves

used in the subgrade – reaction method of active

mailto:[email protected]



INDIAN J. MAR. SCI., VOL. 46, NO. 06, JUNE 2017

lateral pile loading design also include the effects

of global soil displacement.

A method to predict the load – displacement

relationship for single piles subjected to lateral

load, embedded in sand by considering soil

nonlinearity using subgrade reaction, based on the

analysis of 14 full scale lateral pile load tests was

developed15. This method shows promise over

the p-y solutions and predicts upper- and lower-

bound load-deflection curves, which are valuable

guides to making informed engineering decisions.

Algebraic expressions were developed by

researchers which allow the behaviour of flexible

piles under lateral loading, in terms of soil

properties16 &17. The expressions were based on

the results of finite element studies of the

response of a laterally loaded cylindrical pile

embedded in elastic soil with linearly varying

stiffness with depth. In addition, the patterns of

soil movement around a laterally loaded pile,

obtained from the finite element analysis were

used to develop expressions giving interaction

factors between neighbouring piles, by which

means the solution for single piles may be

extended to deal with pile groups.

Many other researchers also studied the behaviour

of piles in a marine structure and the observations

from the parametric study gives a clear idea on

the pile behaviour18, 19& 20.

The governing criterion in the design of pile

foundations to resist lateral loads is the maximum

deflection and the bending moment along the pile

length rather than its ultimate capacity21 & 22.

Bending moment variation along the pile length

and the depth at which the maximum moment

occurs depend on the stiffness of the pile-soil

system and the loading condition. Estimating the

maximum deflection at the pile head is important

to satisfy the serviceability requirements of the

super structure while the bending moment is

required for structural sizing of pile. Among the

pile groupof a Berthing Structure it is essential to

study the effect of change in pile diameter at

various locations so that the pile can be

strengthened in that particular location.

Materials and Methods

A prototype Marine Berthing structure

constructed in Chennai port (India) as shown in

Figure 1 is considered for analysis. This berthing

structure is made of many four bay pile frame

embedded in the sloping ground supporting the

deck slab. Each bay width of the frame is 7.5m

supported by 1m diameter RC piles. Piles are

connected by rigid beams at the top and therefore

made to act as pile frame. Pile frames are placed

at 6m c/c along the longitudinal direction of

berthing structure. The whole system is connected

through the tie rod anchor of 115mm diameter rod

to the dead man wall. Soil slope is 1V:2H on the

site. Finite element software package PLAXIS 3D

FOUNDATION has been used to model the

single frame of this berthing structure.PLAXIS

3D FOUNDATION is a three – dimensional

program especially developed for the analysis of

foundation structures, including off-shore

foundations.

This open pile type marine berthing structure with

tie rod anchor is further analysed by varying the

diameter of piles in different rows of the frame.

Load sharing mechanism of piles in the berthing

structure and the increase in pile diameter with

respect to the pile position provides an efficient

design of the berthing structure. Analysis is done

on two different kind of soil medium as

mentioned below:

Homogeneous layer of sand with a

relative density of 30% considered in the

experimental investigation is used for the

finite element analysis also

The soil profile of Chennai port trust

where this prototype actually exists.

SPT’s (Standard Penetration Test) were

performed to determine the properties of soilthat

actually prevails in a marine environment of

Chennai port trust. Eight boreholes were made on

the site to analyze the critical borehole for which

the analysis is to be done. Depth vs SPT N values

for boreholes BH-1 to BH-8 are plotted in

Figure2. It is observed that the critical borehole is

selected as BH-3. Soil profile for BH-3 is shown

in Figure 3. These parameters are used for

modelling of the berth.

1199

PREMALATHA et al.: INFLUENCE OF CHANGE IN PILE DIAMETER AT VARIOUS LOCATIONS

Figure 1: Typical cross section of the Marine Berthing Structure considered

1200


This open pile type marine berthing structure

with tie rod anchor is further analysed by

varying the diameter of piles in different rows of

the frame. Load sharing mechanism of piles in

the berthing structure and the increase in pile

diameter with respect to the pile position

provides an efficient design of the berthing

structure. Analysis is done on two different kind

of soil medium as mentioned below:

Homogeneous layer of sand with a

relative density of 30% considered

in the experimental investigation is

used for the finite element analysis

also

The soil profile of Chennai port trust

where this prototype actually exists.

SPT’s (Standard Penetration Test) were

performed to determine the properties of soilthat

actually prevailsin a marine environment of

Chennai port trust. Eight boreholes were made

on the site to analyze the critical borehole for

which the analysis is to be done. Depth vs SPT

N values for boreholes BH-1 to BH-8 are plotted

in Figure2. It is observed that the critical borehole

is selected as BH-3. Soil profile for BH-3 is shown

in Figure 3. These parameters are used for

modelling of the berth.

Figure 2: Depth vs SPT N values

Soil layers are defined in Finite element modelling

by means of boreholes. Multiple boreholes are

placed in the geometry to define a non-horizontal

soil stratigraphy or an inclined ground surface.

PLAXIS automatically interpolates layer and

ground surface positions in between the boreholes.

Figure 3: Typical bore hole details

Soil layers and ground surface may be non-

horizontal by using several boreholes at

different locations.

Several forms of finite element analysis with

various approximations have been proposed to

assess the response of piles influenced by

lateral loads. Numerical models involving

FEM can offer several approximations to

predict true solutions. The accuracy of these

approximations depends on the modeller’s

ability to portray what is happening in the

field. Often the problem being modelled is

complex and has to be simplified to obtain a

solution.

The finite element approaches are three-

dimensional finite element analysis, plain

strain analysis and axisymmetric finite

element analysis. Three dimensional finite

element approach has more advantage over

the plane strain finite element approach (or 2D

modelling). In plane strain approach, the piles

are converted into equivalent sheet pile wall

which has a more peripheral area than the

actual pile.

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70

Dep

th i

n (

m)

SPT N values (number of blows)

BH1

BH2

BH3

BH4

BH5

BH6

BH7

BH8

Loose silty sand

-14.0m Es=8,000kN/m

2;

γ = 12.4 kN/m3,Ф = 28⁰

Medium dense silty

sand, -20.0 m

Dense silty sand

-33.0 m

Slightly weathered to

fresh clay

-35.0 m

Highly to moderately

weathered granite

-40.0 m

Es=17,000kN/m2;

γ = 15 kN/m3,Ф = 30⁰

Level 0.0 m

Es=50,000kN/m2;

γ = 19 kN/m3,Ф = 38⁰

Es=52,500kN/m2;

γ = 21 kN/m3,c = 10 t/m

2

Es=120,000kN/m2;

γ = 22 kN/m3,

c = 33.3 t/m2

Rock

1201


When the piles are analysed in groups, this

overlapping area gets accumulated and the

results may not be realistic. PLAXIS 3D

FOUNDATION is a three – dimensional

program especially developed for the analysis

of foundation structures, including off-shore

foundations. Hence a three dimensional finite

element package has been used to model a

single frame of the berthing structure.

Structural Elements:

Structural elements such as beams, floors,

walls and interfaces are based on the line

elements and area elements. The 3-node beam

elements are used to describe semi-one-

dimensional structural objects with flexural

rigidity. Beam elements are slightly different

from 3-node line elements in the sense that

they have six degrees of freedom per node

instead of three, i. e. three translational d. o. f.

s and three rotational d. o. f. s.

Wall elements and floor elements are slightly

different from 8-node quadrilaterals and 6-

node triangles respectively, in the sense that

they have six degrees of freedom per node

instead of three, i. e. three translational d. o. f.

s and three rotational d. o. f. s. These elements

are directly integrated over their cross-section

and numerically integrated using 3 point

Gaussian integration. The position of the

integration points are indicated in the

following Figure 4.

Figure 4:Local numbering and positioning on nodes ( • )

and integration points (X)

Interface elements are different from the 8-

node quadrilaterals in the sense that they have

pairs of nodes instead of single nodes.

Moreover, interface elements have a 3x3 point

Gaussian integration instead of 2x2.

In PLAXIS piles are modelled as embedded

piles. An embedded pile consists of beam

elements with special interface elements

providing the interaction between the beam

and the surrounding soil. Material parameters

of the embedded pile distinguish between the

parameter of beam and parameter of skin

resistance and foot resistance. Beam element

is considered as linear elastic and its

behaviour is defined using elastic stiffness

properties. The embedded interface elements

are considered as elasto-plastic. The failure

behaviour of the embedded pile elements is

defined by their bearing capacity.

Beam elements are 3-node line elements with

six degrees of freedom per node, three

translational degrees of freedom (ux, uy and uz)

and three rotational degrees of freedom ( x,

y, and z). Element stiffness matrices are

numerically integrated from the four Gaussian

integration points (stress points). The element

allows for beam deflections due to shearing as

well as bending. In addition, the element can

change length when an axial force is applied.

The special interface elements are different

from the regular interface elements as used

along walls or volume piles. Since the

embedded pile can be placed arbitrarily in a

soil volume element, these elements will

generally not have common node positions.

Therefore, at the position of the beam element

nodes, virtual nodes are created in the soil

volume element from the element shape

functions. Special interface forms a

connection between the beam element nodes

and these virtual nodes, and thus with all

nodes of the soil volume element.

An embedded pile is a pile composed of beam

elements that can be placed in arbitrary

direction in the sub-soil (irrespective from the

alignment of soil volume elements) and that

interacts with the sub-soil by means of special

interface elements. Interaction may involve a

skin resistance as well as a foot resistance.

The tie rod is taken as the horizontal beam

element. Diaphragm wall and deadman walls

are given using the wall elements. Floor

elements are used to model pile cap. Floors

are structural objects used to model thin

horizontal (two-dimensional) structures in the

8-node plate element 6-node plate element

1202


ground with a significant flexural rigidity

(bending stiffness). Floors are composed of 6-

node triangular plate elements with six

degrees of freedom per node: Three

translational degrees of freedom (ux, uy and uz)

and three rotational degrees of freedom ( x,

y, and z). Element stiffness matrices are

numerically integrated from the 3 Gaussian

integration points (stress points). The element

allows for plate deflections due to shearing as

well as bending. When a plate element is

connected to another plate element (floor or

wall) or a beam element (horizontal or

vertical), they share all degrees of freedom in

the connecting node(s), which implies that the

connection is rigid (moment connection). The

basic geometry parameters include the

thickness d, and the unit weight of the floor

material γ.

A typical application of interfaces would be to

model the interaction between a pile or wall or

beam element and the soil, which is

intermediate between smooth and fully rough.

A value of Rinter = 0.7 is taken for all the

interface elements.

PLAXIS have four different models, namely,

Mohr – Coulomb model (MC), Hardening –

Soil model (HS), Soft – Soil model (SS) and

Soft – Soil – Creep model (SSC) to model

different kinds of soil behaviour.

Mohr Coulomb’s model can be considered as

a first order approximation of real soil

behavior. Soil nodes and pile nodes are

connected by bilinear Mohr-Coulomb

interface elements. This allows an

approximate representation of the

development of lateral resistance with relative

soil-pile movement and ultimately the full

limiting soil pressure acting on the piles. Mohr

Coulomb’s model is considered as a first order

approximation of real soil behaviour. This

elastic perfectly plastic model requires 5 basic

input parameters, namely

E :Young’s modulus [kN/m2]

ν :Poisson’s ratio [-]

:Friction angle [0]

c :Cohesion [kN/m2]

:Dilatancy angle [

0]

This is a well known and a basic soil model.

The soil nodes and pile nodes are connected

by bilinear Mohr-Coulomb interface elements.

This allows an approximate representation of

the development of lateral resistance with

relative soil-pile movement and ultimately the

full limiting soil pressure acting on the piles.

Mesh Generation

The PLAXIS 3D FOUNDATION program

allows for an automatic generation of

unstructured 2D finite element meshes based

on the top view. There are options for global

and local mesh refinement. From this 2D

mesh, a 3D mesh is automatically generated,

taking into account the soil stratigraphy and

structure levels as defined in the bore holes

and work planes. Figure 5 shows a typical 3D

finite element model for a single frame of a

berthing structure without tie rod anchor.

Figure 6 shows the typical three dimensional

finite element mesh generated in sloping

ground with tie rod anchor. The areas near the

pile and the top beam has a large stress

concentrations or large deformation gradients.

Hence it is desirable to have a more accurate

(finer) finite element mesh whereas the other

part of the geometry does not require a fine

mesh. Local refinement is done for 2 times on

the cluster surrounding the piles in the 2D

mesh generation, and then the 3D mesh is

generated. Figure 7 shows the stress contour

developed after application of the mooring

force.

Figure 5:Three dimensional finite element model

generated for SG-WOT-MF

1203


Figure 6:Three dimensional finite element mesh

generated for SG-WT-MF

Figure 7: Stress contour for SG-WOT-MF after

application of the mooring force

Validation of Finite Element model

The FE model developed in the previous

section is validated through results of a single

pile test and the results of the scale model

experiments. The FE predictions are also

compared with the results obtained using the

classical solutions proposed by various

researchers and thus the FE model is

validated. Upon the validation, the FE model

is employed to predict the behaviour of the

experimentally tested specimens under

different load and ground profile condition.

Further parametric study is carried out and the

results are presented in this chapter.

A model pile of 25.4 mm diameter, 1mm wall

thickness and 750 mm long is embedded in a

horizontal ground of homogeneous soil of

relative density 30%. This pile was subjected

to monotonically increasing lateral load and

the corresponding tip end deflection was

measured. The lateral load vs deflection was

plotted and the same is used to validate the FE

model.

The test conditions were simulated through

the developed FE model and the

corresponding load vs deflection was plotted.

The comparison between the experimental and

FE predictions are shown in Figure 8. For this

single pile test condition, the established

classical solutions developed by Brom’s

(1981) and Tomlinson (1987) are employed

over the present experimental values and the

obtained results are plotted in the same Figure

8. Also, similar kind of experimental results

published by Muthukkumaran et al. (2007)

and Almas Begum et al. (2008) are plotted for

comparison purposes. From the comparison shown in Figure 8, it

can be easily noted that the FE model is

capable of predicting the lateral load vs

deflection behaviour of a single pile to an

acceptable accuracy and thus validated.

Figure 8: Lateral load vs deflection (relative density

30%)

Results and Discussion

A three dimensional Finite Element Model of

the scale down model frame is created using

the software 3D PLAXIS foundation. The

same parameters of the soil and its density,

pile, top connecting beam, tie rod anchor,

slope etc that were used in the experimental

investigation are adopted for the finite element

modelling.

A detailed study on the load sharing

mechanism of piles in the pile group of open

pile type marine berthing structure can give an

exact idea of the piles that needs to be

strengthened. Hence the distribution of load

-7

-6

-5

-4

-3

-2

-1

0

0 20 40 60 80 100

La

tera

l d

efl

ecti

on

(m

m)

Lateral Load (N)

Brom's (1981)

Tomlinson (1987)

Muthukumaran et al. (2007 experimental study)

Almas Begum et al. (2008 experimental study)

Experiment (present study)

FEM (present study)

1204


among the piles is of great importance. Figure

9 and Figure 10 shows the bending moment

variation against depth along the length of the

front, intermediate and rear piles of the

berthing structure subjected to mooring force

in homogeneous soil and layered soil. The rear

pile carries the max load compared to other

piles of the frame. The depth of fixity of the

rear pile is less compared to other

piles.Therefore, if the diameter of the rear pile

is increased, it will result in an effective

system.

Figure 9:Bending Moment Variation against Depth

(diameter of all piles =1m) subjected to mooring force in

homogeneous soil

Figure 10:Bending Moment Variation against Depth (all

piles dia 1m) in layered soil

The marine berthing structure is analysed for

various different cases to arrive at an effective

and economical one. Initially all the piles are

taken as 1m diameter. The parametric study

on the above structure is done by varying the

diameter of the piles in various locations.

Following are the cases considered in the

analysis:

(i) COMBINATION I - Considering

the diameters of all the piles as

1m.

(ii) COMBINATION II - Increasing

the diameters of all the piles to

1.2m.

(iii) COMBINATION III - Increasing

the diameter of front and rear pile

only to 1.2m

(iv) COMBINATION IV - Increasing

the diameter of only rear pile to

1.2m.

(v) COMBINATION V - Increasing

the diameter of last two rows of

rear pile to 1.2m.

Analysis is done for both mooring force and

berthing force.

Figure 11 shows the deflection of the structure

with and without tie rod anchor subjected to

mooring force for all the above five cases in

homogeneous soil of relative density 30%.

When the diameters of all the piles are 1m,

there is a reduction in deflection of 18.55%.

When the entire pile diameter is increased to

1.2m, the deflection is reduced by 17.9%. For

combination 1, combination 2 and

combination 3, the deflection is reduced by

19.7%, 18.36% and 19.62% respectively.

While comparing the other cases, Case III-

Combination 1 which contains the increased

diameter of first and last pile also reduces the

deflection in an effective manner comparative

to the case II (with all pile dia 1.2m).

Moreover increasing the cost of all piles is not

an economical solution.

-35

-30

-25

-20

-15

-10

-5

0

-2000 -1500 -1000 -500 0 500 1000

Dep

th (

m)

Bending Moment (KNm)

Front pile

Intermediate pile

Rear pile

-35

-30

-25

-20

-15

-10

-5

0

-2000 -1500 -1000 -500 0 500 1000

Dep

th (

m)

Bending Moment (kNm)

Front pile

Intermediate pile

Rear pile

Sea side Land side

Sea side Land side

Land side Sea side

Sea side Land side

Land side Sea side

1205


Figure 11:Deflection of the structure with and without

tie rod anchor forvarious combination of pilediameter

subjected to mooring force in homogeneous soil



berthing force for various combination of pile

diameter. Even though the deflection

corresponding to berthing force is less

compared to the mooring force, the similar

kind of behavior is observed in this case also.

The percentage reduction in deflection is

given in Table 1.


tie rod anchor for various combination of pile diameter

subjected to berthing force in homogeneous soil



mooring force for all the above five cases in

layered soil. When the diameters of all the

piles are 1m, there is a reduction in deflection

of 26%. When the entire pile diameter is

increased to 1.2m, the deflection is reduced by

27%. For combination 1, combination 2 and

combination 3, the deflection is reduced by

26.7%, 25.66% and 28.9 % respectively.

Table 1: Percentage reductions in Deflection for various

Combinations of pile diameters subjected to Berthing

force and Mooring force.

S.No Details Homogeneous soil

RD=30%

Reduction in

Deflection

Layered Soil

Reduction in

Deflection

Mooring

Force

Berthing

Force

Mooring

Force

Berthing

Force

CASE

-I

All piles

dia 1m

18.55% 11.27%% 25.98% 12.64%

CASE

-II

All piles

dia 1.2m

17.9% 21.38% 27% 16%

CASE

-III

Combin

ation 1

19.7% 14.2% 26.7% 15.13%

CASE

-IV

Combin

ation 2

18.36% 13.29% 25.66% 13.37%

CASE

-V

Combin

ation 3

19.62% 17.5% 28.9% 14.63%

While comparing the other cases, Case III-

Combination 1 which contains the increased

diameter of first and last pile also reduces the

deflection in an effective manner comparative

to the case II.


tie rod anchor for various combination of pile

diametersubjected to mooring force in layered soil



berthing force for various combination of pile

diameter. Even though the deflection

corresponding to berthing force is less

compared to the mooring force, the similar

kind of behavior is observed in this case also.

0

10

20

30

40

50

60

70

80

69.032

62.1566.32 67.54

65.54

56.23

51.0253.25 55.14

52.68

Defl

ecti

on

(m

m)

MF

without tierod

with tierod

comb 1dia 1.2dia 1 comb 3comb 2

0

5

10

15

20

2524.3

20.87922.167

23.54 2321.56

16.416

19.01520.411

18.98

Defl

ecti

on

(m

m)

BF

without tierod

with tierod


0

10

20

30

40

50

60 56.485

48.26

52.1454.241

52.31

41.811

35.2138.2

40.3237.185

Defl

ecti

on

(m

m)

MF-layer

without tierod

with tierod


1206



tie rod anchor for various combination of pile diameter

subjected to berthing force layered soil

Figure 15 to 18 shows the bending moment

variation against depth of front pile for

various cases in homogeneous layer of sand.

Figure 19 to 22 shows the bending moment

variation against depth of front pile for

various cases in layered soil

Figure 15:Bending Moment Variation against Depth for

SG-WOT-MF for various cases in homogeneous soil of

RD=30%


SG-WT-MF for various casesin homogeneous soilof

RD=30%.


SG-WOT-BF for various casesin homogeneous soil of

RD=30%.


SG-WT-BF for various casesin homogeneous soil of

RD=30%.


SG-WOT-MF for various cases in layered soil.

0

2

4

6

8

10

12

14

16

18

2018.2

15

17.203 17.662

16.415.9

12.6

14.615.3

14

Defl

ecti

on

(m

m)

BF-layer

without tierod

with tierod


-35

-30

-25

-20

-15

-10

-5

0

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000

Dep

th (

m)


WOT-MF-dia1

WOT-MF-dia1.2

WOT-MF-comb1

WOT-MF-comb2

WOT-MF-comb3

-35

-30

-25

-20

-15

-10

-5

0

-1000 -800 -600 -400 -200 0 200 400 600 800

Dep

th (

m)


WT-MF-dia1

WT-MF-dia1.2

WT-MF-comb1

WT-MF-comb2

WT-MF-comb3

-35

-30

-25

-20

-15

-10

-5

0

-300 -200 -100 0 100 200

Dep

th (

m)


WOT-BF-dia1

WOT-BF-dia1.2

WOT-BF-comb1

WOT-BF-comb2

WOT-MF-comb3

-35

-30

-25

-20

-15

-10

-5

0

-300 -200 -100 0 100 200

Dep

th (

m)


WT-BF-dia1

WT-BF-dia1.2

WT-BF-comb1

WT-BF-comb2

WT-BF-comb3

-35

-30

-25

-20

-15

-10

-5

0

-2000 -1500 -1000 -500 0 500 1000 1500

Dep

th (

m)


WOT-MF-dia1

WOT-MF-dia1.2

WOT-MF-comb1

WOT-MF-comb2

WOT-MF-comb3

1207



SG-WT-MF for various cases in layered soil


SG-WOT-BF for various cases in layered soil


SG-WT-BF for various cases in layered soil

From the above figures, it is seen that the rear

pile carries the maximum load, hence

increasing the diameter of rear piles will give

an effective system of reducing deflection.

Considering CASE I to V, there is a reduction

in the bending moment of the pile when tie

rod anchors are provided, but there is no

change in the depth of fixity.

Considering CASE II (where all the diameter

of piles is increased to 1.2m, the overall

stiffness of the structure gets increased and

hence the load shared between piles and the

tie rod anchor gets altered. More load is taken

by the structure itself and hence the bending

moment on the pile is more compared to

CASE I, II and V.

Considering CASE III- Combination 1 where

the diameters of front and rear piles are

increased, there is an increased load carrying

capacity of the front and rear pile due to the

increased cross sectional area. The BM of

front pile is more compared to CASE I, IV

and V. This transfer of load from the rear pile

to front pile, redistributes the overall load

sharing mechanism of pile group and an

effective system is achieved. However the

optimum length of this anchor rod

corresponding to the soil condition plays a

major role in arriving at an effective system.

As the rear pile (on the crest) carries the max

load in sloping ground, considering CASE IV-

combination 2, increasing the diameter of the

only rear piles helps in carrying the load that

is transferred to it.

Considering CASE V-combination 3,

increasing the diameter of last two rear piles

again helps in carrying the higher load

transferred to them. But there is no transfer of

load to the front piles and hence the BM of

front pile remains same as CASE I, IV and V.

Whereas in CASE III, there is a transfer of

load from rear pile to front pile. Hence CASE

III is more effective than CASE V.

From the bending moment variation along its

depth for various cases, it is observed that not

much reduction is observed in positive

bending moment, but there is a reduction in

negative bending moment of the piles.

-35

-30

-25

-20

-15

-10

-5

0

-2000 -1600 -1200 -800 -400 0 400 800 1200

Dep

th (

m)


WT-MF-dia1

WT-MF-dia1.2

WT-MF-comb1

WT-MF-comb2

WT-MF-comb3

-35

-30

-25

-20

-15

-10

-5

0

-400 -300 -200 -100 0 100 200

Dep

th (

m)


WOT-BF-dia1

WOT-BF-dia1.2

WOT-BF-comb1

WOT-BF-comb2

WOT-BF-comb3

-35

-30

-25

-20

-15

-10

-5

0

-400 -300 -200 -100 0 100 200 300

Dep

th (

m)


WT-BF-dia1

WT-BF-dia1.2

WT-BF-comb1

WT-BF-comb2

WT-BF-comb3

1208


Conclusions The diameter of the piles at various locations

in a row of a marine berthing structure on a

sloping ground is varied. Results showed that

increasing the diameter of piles in the slope

crest increases the lateral load carrying

capacity of the pile which carries the

maximum load, whereas increasing the pile

diameter on the down slope redistributes the

overall load on the frame. Hence all the piles

carry more loads when compared to the earlier

case. It is concluded that increasing the

diameter of rear piles decreases the deflection

of the structure to a large extent. Increasing

the diameter of the front and rear piles

distributes the load more evenly among the

piles of the berthing structure.

Acknowledgement

Authors are grateful to the faculties of

Department of Civil Engineering, National

Institute of Technology, Tiruchirappalli for

providing facilities and encouragement to

carry out the above research work.

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1209

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