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
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.
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PREMALATHA et al.: INFLUENCE OF CHANGE IN PILE DIAMETER AT VARIOUS LOCATIONS
Figure 1: Typical cross section of the Marine Berthing Structure considered
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INDIAN J. MAR. SCI., VOL. 46, NO. 06, JUNE 2017
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
PREMALATHA et al.: INFLUENCE OF CHANGE IN PILE DIAMETER AT VARIOUS LOCATIONS
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
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INDIAN J. MAR. SCI., VOL. 46, NO. 06, JUNE 2017
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
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PREMALATHA et al.: INFLUENCE OF CHANGE IN PILE DIAMETER AT VARIOUS LOCATIONS
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
INDIAN J. MAR. SCI., VOL. 46, NO. 06, JUNE 2017
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
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PREMALATHA et al.: INFLUENCE OF CHANGE IN PILE DIAMETER AT VARIOUS LOCATIONS
Figure 11:Deflection of the structure with and without
tie rod anchor forvarious combination of pilediameter
subjected to mooring force in homogeneous soil
Figure 12 shows the deflection of the structure
with and without tie rod anchor subjected to
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.
Figure 12:Deflection of the structure with and without
tie rod anchor for various combination of pile diameter
subjected to berthing force in homogeneous soil
Figure 13 shows the deflection of the structure
with and without tie rod anchor subjected to
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.
Figure 13:Deflection of the structure with and without
tie rod anchor for various combination of pile
diametersubjected to mooring force in layered soil
Figure 14 shows the deflection of the structure
with and without tie rod anchor subjected to
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
comb 1dia 1.2dia 1 comb 3comb 2
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
comb 1dia 1.2dia 1 comb 3comb 2
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INDIAN J. MAR. SCI., VOL. 46, NO. 06, JUNE 2017
Figure 14:Deflection of the structure with and without
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%
Figure 16:Bending Moment Variation against Depth for
SG-WT-MF for various casesin homogeneous soilof
RD=30%.
Figure 17:Bending Moment Variation against Depth for
SG-WOT-BF for various casesin homogeneous soil of
RD=30%.
Figure 18:Bending Moment Variation against Depth for
SG-WT-BF for various casesin homogeneous soil of
RD=30%.
Figure 19:Bending Moment Variation against Depth for
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
comb 1dia 1.2dia 1 comb 3comb 2
-35
-30
-25
-20
-15
-10
-5
0
-1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000
Dep
th (
m)
Bending Moment (KNm)
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)
Bending Moment (KNm)
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)
Bending Moment (KNm)
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)
Bending Moment (KNm)
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)
Bending Moment (kNm)
WOT-MF-dia1
WOT-MF-dia1.2
WOT-MF-comb1
WOT-MF-comb2
WOT-MF-comb3
1207
PREMALATHA et al.: INFLUENCE OF CHANGE IN PILE DIAMETER AT VARIOUS LOCATIONS
Figure 20:Bending Moment Variation against Depth for
SG-WT-MF for various cases in layered soil
Figure 21:Bending Moment Variation against Depth for
SG-WOT-BF for various cases in layered soil
Figure 22:Bending Moment Variation against Depth for
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)
Bending Moment (KNm)
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)
Bending Moment (kNm)
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)
Bending Moment (kNm)
WT-BF-dia1
WT-BF-dia1.2
WT-BF-comb1
WT-BF-comb2
WT-BF-comb3
1208
INDIAN J. MAR. SCI., VOL. 46, NO. 06, JUNE 2017
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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