6-13-17022017 SETTLEMENT ANALYSIS OF PILED RAFT FOUNDATION IN CLAY OF SOFT TO MEDIUM CONSISTENCY BY NONLINEAR FINITE ELEMENT METHOD

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International Journal of Latest Research in Science and Technology
Volume 6, Issue 1: Page No.41-45,January-February 2017
http://www.mnkjournals.com/ijlrst.htm
ISSN (Online):2278-5299
SETTLEMENT ANALYSIS OF PILED RAFT
FOUNDATION IN CLAY OF SOFT TO MEDIUM
CONSISTENCY BY NONLINEAR FINITE
ELEMENT METHOD
1
Dr.D.K.Maharaj, 2Dr.Sanjeev Gill
1
Director,Principal, Professsor
Guru Nanak Institute of Technology (GNIT), Guru Nanak Institutions (GNI)
Mullana, Ambala, Haryana, India
2
Principal, JBIT, Dehradun, India
Abstract - In this paper a single pile with equivalent size of raft has been taken from an Infinite piled raft. One fourth of piled raft with
equivalent area of raft has been taken from a single pile with equivalent area of raft. The soil, pile and raft have been discretized as eight
nodded brick elements. The soil has been idealized as Extended Drucker-Prager yield criterion. The material behaviour of pile and raft
has been considered as linear elastic medium. The load settlement curves are linear in the earlier portion of the curves and then it become
nonlinear This nonlinearity is maximum at larger loading intensity and minimum at smaller loading intensity. The maximum settlement is
for pile having length to diameter ratio of 10 and minimum for pile having length to diameter ratio equal to 50. The marginal difference
for settlement between the curves is maximum at loading intensity equal to 50 kN/m 2 and minimum at loading intensity of 10 kN/m2. In the
load settlement curves plotted for various spacing to diameter ratio the marginal difference for settlement between the curves is very very
small at length to diameter equal to 10 and than it becomes better and better with increase in length to diameter ratio of pile.
LITERATURE REVIEW
Hongladaromp et.al (1973) studied the interaction of a
rectangular pile cap with subgrade to determine the sharing of
load on piles and the subgrade. Employing the finite
difference technique a parametric study was carried out. They
found that the resistance of the subgrade has considerable
effect on settlement of footing and should be taken into
consideration in the analysis.
Brown and Wiegner (1975) presented results for load taken
by piles, maximum displacements, differential displacements
due to uniformly distributed load applied to a smooth strip
footing which is supported by piles on a deep homogeneous
isotropic elastic foundation.
Wiesner(1980) performed laboratory tests on four model
piled raft foundations having circular raft. The experimental
load-settlement and load-moment curves were compared with
the results of theoretical study.
EI-Mossallamy (1989) presented in his paper the pile-raftsoil interaction. The analysis were carried out under the
assumption of linear elastic behaviour of raft, piles and half
space, unsolved bond ie. no slip between piles and half space.
The load sharing between pile and raft, the effect of length of
pile in reducing settlement are discussed.
Clancy and Randolph (1993) describe a ‘hybrid’ approach
for the analysis of piled raft foundations, based on a load
transfer treatment of individual piles, together with elastic
interaction between different piles and with the raft.
Parametric studies are presented showing the effect of factors
such as raft stiffness and pile spacing, length and stiffness.
Prakoso and Kulhawy (2001). examined raft foundations
enhanced with deep foundation elements (typically piles),
simply known as piled rafts. Illustrative piled rafts were
analyzed using simplified linear elastic plane strain finite
ISSN:2278-5299
element models The results were synthesized into an updated,
displacement-based, design methodology for piled rafts.
Small and Zhang (2002) presents a new method of
analysis of piled raft foundations in contact with the soil
surface. The soil is divided into multiple horizontal layers.
The raft is modeled as a thin plate and the piles as elastic
beams. Finite layer theory is employed to analyze the layered
soil while finite element theory is used to analyze the raft and
piles Comparisons show that the results from this method
agree closely with those from the finite element method.
Al-Mosawi et.al (2011) present experimental study to
investigate the behavior of piled raft system in sandy soil. A
small scale “prototype” model was tested in a sand box with
load applied to the system through a compression machine.
The settlement was measured at the center of the raft, strain
gages were used to measure the strains and calculate the
total load carried by piles.
El-Garhy et.al (2013) conducted an experimental program
on model piled rafts in sandy soil. The model piles beneath
the rafts are closed ended displacement piles installed by
driving. Three lengths of piles are used in the experiments to
represent slenderness ratio, L/D, of 20, 30 and 50,
respectively. The dimensions of the model rafts are 30 cm ×
30 cm. The results of the tests show the effectiveness of using
piles as settlement reduction measure with the rafts. As the
number of settlement reducing piles increases, the load
improvement ratio increases and the differential settlement
ratio decreases.
Raut et.al (2015) present model laboratory test on piled
raft foundation to investigate load sharing ratio. Structural
mild steel bars of 10 mm dia and 1 m long are used as piles.
Mild steel plate of 10 mm thick and 300 mm x 300 mm
41
International Journal of Latest Research in Science and Technology.
FINITE ELEMENT ANALYSIS
Fig.1 shows the finite element discretization .
Discretization shows one fourth of piled raft with equivalent
area of raft taken from a single pile with equivalent area of
raft from pile forest model The soil, pile and raft have been
discretized as eight nodded brick elements. The material
behaviour of pile and raft has been considered as linear
elastic medium. The soil has been idealized as an Extended
Drucker-Prager model.
Load (kN/m2)
0
10
20
30
40
50
0
Settlement (mm)
square plate is taken as raft foundation. On raft foundation
(steel plate) with piles (steel bars) load is applied gradually
and ultimate bearing capacity is calculated. Total load taken
by piles is calculated and load sharing ratio of raft and pile is
calculated.
Field measurements as reported by Hooper(1973),
Cooke(1981),Schwab(1991), Franke (1991), Poulos (1994)
and Yamashita (1994) give very useful information for load
transfer and settlement behaviour of piled raft.
L/d=10,
s/d=2.5
-10
L/d=20,
s/d=2.5
-20
-30
L/d=30,
s/d=2.5
-40
L/d=40,
s/d=2.5
-50
-60
Fig.2 Load settlement curve
L/d=50,
s/d=2.5
Fig.3 shows the load settlement curve at spacing to diameter
ratio equal to 5 for varying length to diameter ratio for
different loading intensity. The load settlement curves are
nonlinear. This nonlinearity is maximum at larger loading
intensity and minimum at smaller loading intensity. The
marginal difference of settlement between the curves is
maximum at loading intensity equal to 50 kNm2 and
minimum at loading intensity 10 kN/m2. With increase in
spacing to diameter ratio the marginal difference of
settlement between the curves decreases.
Load (kN/m2)
0
10 20 30 40 50
Settlement (mm)
0
-10
L/d=10, s/d=5
-20
L/d=20, s/d=5
-30
L/d=30 ,s/d=5
-40
L/d=40, s/d=5
L/d=50, s/d=5
-50
-60
Fig.3 Load settlement curve
RESULTS AND DISCUSSIONS
Fig.2 shows the load settlement curve for different length
to diameter ratio for varying loading intensity at spacing to
diameter ratio equal to 2.5. The nature of curves are
nonlinear.This nonlinearity is maximum at larger loading
intensity and minimum at smaller loading intensity. The
maximum settlement is for pile having length to diameter
ratio of 10 and minimum for pile having length to diameter
ratio equal to 50. The marginal difference for settlement
between the curves is maximum at loading intensity equal to
50 kN/m2 and minimum at loading intensity of 10 kN/m2.
ISSN:2278-5299
Fig.4 shows load settlement curves for various length to
diameter ratio and loading intensity. Each of the curve is
nonlinear. The initial portion of the curves is linear. The
marginal difference of settlement between the curves for
spacing to diameter ratio 10 is smaller than that for spacing to
diameter ratio equal to 5. This is because the raft size is
greater at spacing to diameter 10 and the raft takes more load.
42
International Journal of Latest Research in Science and Technology.
Load (kN/m2)
0
10 20
30
40
Load (kN/m2)
50
0
-10
L/d=10, s/d=10
-20
L/d=20, s/d=10
-30
L/d=30, s/d=10
-40
L/d=40, s/d=10
-50
L/d=50, s/d=10
-60
20
30
40
50
S/d=2.5, L/d=10
-10
-20
S/d=5, L/d=10
-30
S/d=10, L/d=10
-40
-50
S/d=15, L/d=10
-60
Fig.6 Load settlement curve
Fig.4 Load settlement curve
Fig.5 shows the load vs settlement curves for various length
to diameter ratio at spacing to diameter ratio equal to 15. As
for spacing to diameter ratio 2.5,5,10 this curve is also
nonlinear.The marginal difference between the settlement of
the curves is minimum i.e smaller than that with spacing to
diameter ratio equal to 2.5,5 and10. This is because the raft
size is greater and the raft takes more load.
Fig.7 shows the load settlement curve for length to diameter
ratio 20 for various spacing to diameter ratio and loading
intensity. The curves are nonlinear and the marginal
difference for settlement between the curves is better than in
Fig.6.
Load (kN/m2)
0
Load (kN/m2)
10
20
30
40
10
20
30
40
50
0
50
0
-10
-20
-30
L/d=10, s/d=15
L/d=20, s/d=15
L/d=30, s/d=15
-40
L/d=40, s/d=15
-50
L/d=50, s/d=15
Settlement (mm)
0
Settlement (mm)
10
0
Settlemenet (mm)
Settlement (mm)
0
-10
-20
S/d=2.5, L/d=20
S/d=5, L/d=20
-30
-40
-50
S/d=10, L/d=20
S/d=15, L/d=20
-60
Fig.7 Load settlement curve
-60
Fig.5 Load settlement curve
Fig.6 shows the load settlement curve for piled raft
foundation for length to diameter ratio 10 for various spacing
to diameter ratio. Even in this case the load settlement curves
are nonlinear. The marginal difference between the
settlement curves is very very small.
ISSN:2278-5299
Fig.8 shows the load settlement curve for length to diameter
ratio 30 for various spacing to diameter ratio and loading
intensity. The curves are nonlinear and the marginal
difference for settlement between the curves is better than in
Fig.6 and Fig.7.
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International Journal of Latest Research in Science and Technology.
Load (kN/m2)
0
10 20 30 40 50
Settlement (mm)
0
S/d=2.5, L/d=30
-10
-20
S/d=5, L/d=30
-30
S/d=10, L/d=30
-40
-50
S/d=15, L/d=30
-60
Fig.8 Load settlement curve
Fig.9 shows the load settlement curve for length to
diameter ratio 40 for various spacing to diameter ratio and
loading intensity. The curves are nonlinear and the marginal
difference for settlement between the curves is better than in
Fig.6 ,Fig.7 and Fig.8
Fig.10 shows the load settlement curve for length to
diameter ratio 50 for various spacing to diameter ratio and
loading intensity. The curves are nonlinear and the marginal
difference for settlement between the curves is better than in
Fig.6 ,Fig.7 ,Fig.8 and Fig.9
CONCLUSIONS
Based on nonlinear finite element analysis the following
conclusions have been made.
The load settlement curves are linear in the earlier portion
of the curves and then it become nonlinear This nonlinearity
is maximum at larger loading intensity and minimum at
smaller loading intensity. The maximum settlement is for pile
having length to diameter ratio of 10 and minimum for pile
having length to diameter ratio equal to 50. The marginal
difference for settlement between the curves is maximum at
loading intensity equal to 50 kN/m2 and minimum at loading
intensity of 10 kN/m2. In the load settlement curves plotted
for various spacing to diameter ratio the marginal difference
for settlement between the curves is very very small at
length to diameter equal to 10 and than it becomes better and
better with increase in length to diameter ratio of pile.
REFERENCES
1.
Al-Mosawi ,M.J., Y. Fattah,M. and Al-Zayadi,A.A.O (2011)
Experimental Observations on the Behavior of a Piled Raft
Foundation, Journal of Engineering, Volume 17, No. 4
2.
Brown , P.T. and Wiesner, T.J.(1975) The behaviour of uniformly
loaded piled strip footing, Soils and Foundations, 15(4),13-21
3.
Clancy, P. and Randolph, M.F.(1993)An Approximate Analysis
Procedure for Piled Raft Foundations, International Journal for
Numerical and Analytical Methods in Geomechanics,Vol.17, No.12,
pp.849–869
4.
Cooke, R.W., Bryden-Smith, D.W. and Gooch(1981) Some
observations of the foundation loading and settlement of a multistorey building on piled raft foundation in London clay,
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Der-Guey Lin and Zheng-Yi Feng (2006) A Numrical Study
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El-Garhy,B., Galil,A.A., Abdel-Fattah A.A.,Raia,M.A.(2013)
Behavior of Raft on Settlement Reducing Piles: Experimental Model
Study, Journal of Rock Mechanics and Geotechnical
Engineering,Vol.5 ,pp389–399
7.
EI-Mossallamy (1989) Analysis of pile-raft-soil interaction, M.Sc
Thesis, faculty of engineering, Ain ShamsUniversity, Cairo,
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a Structural Engineeringof Ain Shams University under the same
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8.
Franke, E.(1991)Measurements beneath piled rafts, key note lecture
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Load (kN/m2)
Settlement (mm)
0
10 20 30 40 50
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
S/d=2.5, L/d=40
S/d=5, L/d=40
S/d=10, L/d=40
S/d=15, L/d=40
Fig.9 Load settlement curve
0
Load (kN/m 2)
10 20 30 40 50
0
Settlement (mm)
S/d=2.5, L/d=5
0
-10
S/d=5, L/d=50
-20
-30
S/d=10, L/d=5
0
-40
S/d=15, L/d=5
0
-50
Fig.10 Load settlement curve
ISSN:2278-5299
10. Hopper, J.A.(1973)Observations on the behaviour of a piled raft
foundation in London clay, Proceedings of Institution of Civil
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foundations. 3rd InternationalConference on DEEP FOUNDATION
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Ratio of Piled Raft Foundation, 50th INDIAN GEOTECHNICAL
CONFERENCE 17th – 19th DECEMBER 2015, Pune, Maharashtra,
India Venue: College of Engineering (Estd. 1854), Pune, India
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International Journal of Latest Research in Science and Technology.
14. Schwab,H.H., Gundling,N. and Lutz,B.(1991)Monitoring pile raft
soil interaction, Proceedings of Symposium on Field Measurements
in Geotechnics, Sorum, Balkema, Rotterdam,117-127.
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Foundations under Lateral and Vertical Loading International
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Foundations
17. Journal of the Geotechnical Engineering Division, 1980, Vol. 106,
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ISSN:2278-5299
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