PERFORMANCE OF STRIP FOOTINGS ON SLOPE REINFORCED WITH INCLINED PILE

http://www.iaeme.com/IJCIET/index.asp 211 editor@iaeme.com
International Journal of Civil Engineering and Technology (IJCIET)
Volume 7, Issue 3, May–June 2016, pp. 211–222, Article ID: IJCIET_07_03_021
Available online at
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3
Journal Impact Factor (2016): 9.7820 (Calculated by GISI) www.jifactor.com
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
PERFORMANCE OF STRIP FOOTINGS ON
SLOPE REINFORCED WITH INCLINED
PILE
Dr. S. S. Pusadkar
Associate Professor, Department of Civil Engineering, Government College of
Engineering, Amravati, M.S, India
A. U. Mankar
P.G. Scholar, Department of Civil Engineering, Government College of Engineering,
Amravati, M.S, India
ABSTRACT
The footing that placed on slope surface results in decreasing the bearing
capacity of soil. The pile reinforcing the slope may affect the bearing capacity
of footing and factor of safety of slope. The piles installed within the slope
mechanically provide a resistance to slope system along the failure surface.
The present work was focused on the analysis of strip footing behavior on
slope with and without pile using a finite element software PLAXIS 2D. The
various parameters considered for present work includes location of pile from
slope crest, inclination of pile, effect of pile length and effect of width of load.
The results indicated that stabilizing pile has a significant effect in improving
the bearing capacity and factor of safety of slope. The bearing capacity of
footing was found to be maximum when slope was reinforced by pile at crest.
For smaller width of strip, the factor of safety of slope was maximum when
pile is placed at crest while for larger width the pile location at 0.5 horizontal
widths of slope gave maximum factor of safety.
Key words: Strip Footing, pile, PLAXIS 2D, Bearing Capacity, Factor of
safety.
Cite this Article: Dr. S. S. Pusadkar and A. U. Mankar, Performance of Strip
Footings on Slope Reinforced with Inclined Pile, International Journal of
Civil Engineering and Technology, 7(3), 2016, pp. 211–222.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3

Dr. S. S. Pusadkar and A. U. Mankar
INTRODUCTION
Many situations necessitates the placement of footings on sloping surfaces or adjacent
to a slope crest, e.g. footings for bridge abutments on sloping embankments, small to
medium size building adjacent to slope crest. When a footing is located on a sloping
ground, the bearing capacity of the footing may be significantly reduced, depending
on the location of the footing with respect to the slope. Over years, the subject of
stabilizing the earth slope has become one of the most interesting areas for scientific
research and attracted a great deal of attention. Slope stability can be increased in
different ways, such as modifying the slope surface geometry, using soil
reinforcement, or installing continuous or discrete retaining structures such as walls or
piles. The use of stabilizing piles to support an active earth slope has been considered
to be one of the important slope reinforcement techniques in the last few decades.
These piles, which can be driven at the crest or within the slope itself, act as resisting
members and are usually subjected to lateral forces by the horizontal movements of
the surrounding soil. Here the study will be carried out using PLAXIS 2D for slope
subjected to strip footing and reinforced using pile at different location.
LITERATURE REVIEW
The slopes naturally made or manmade are being used in construction of structures on
or nearby them. These structures are located at various places on slopes or on
embankment side. The presence of structure on or nearby slope may disturb the
stability of slopes or lead to sustain low bearing load. The slopes safety or bearing
load can be improved by providing suitable measures. The various researchers took
effort to suggest alternative methods. The present work is related to improvement in
slope stability by reinforcing the slopes with pile. The work carried by various authors
is illustrated in brief to understand the extent of work carried out.
The slope reinforced with piles using the finite element method was analyzed by
Cai and Ugai (2000). It was concluded that the maximum safety factor for the slope
can be achieved when the piles are located in the middle of the slope and the pile head
restrained. The numerical comparison of predictions by limit equilibrium analysis and
3D numerical analysis for a slope–pile system was carried out by Won et al. (2005). It
was observed that for stability to be improved optimally, the piles should be installed
in the middle of the slope and with restrained pile head.
Yang et al. (2011) studied the effect of embedded length of piles for slope
reinforced with piles by varying parameters such as pile head condition viz. free,
fixed, hinged and non-rotated head, embedded pile length. It was concluded that a
restrained pile head was recommended and free head should be avoided to stabilize
the slope.
Gullu (2013) studied the effect of pile on slope stability by PLAXIS 2D by
changing the location of pile at different position within slope. It was concluded that
factor of safety of slope-pile system increases with the increased the row of pile and
suggests using either the single row pile at the toe or two-row piles at the toe and
middle of slope in practice.
Wang and Zhang (2013) conducted centrifuge testing and observed the behavior
of pile in cohesive soil slopes with varying inclination of slope and pile head
conditions. It was observed that the stability level of the slope was increased by
compression and shear effect provided by pile.
From the above discussion it was observed that the previous studies on pile-
stabilized slope were done for improvement of slope only. The little work was carried

Performance of Strip Footings on Slope Reinforced with Inclined Pile
out on the improvement of load-carrying characteristics of shallow footings supported
on pile-stabilized slope. The main objectives of the present study was to study the
effect of various parameters of footing, location of pile and load inclination on factor
of safety of slope and bearing capacity of footing.
NUMERICAL ANALYSIS
The geometry of the finite element soil model adopted in the PLAXIS 2D analysis
was 5H X 7H with the width of strip footing as 1.5m. The analysis was carried out for
different pile locations and L/B ratio with different pile inclinations. The details of the
parameter studied are as shown in Table 1.
Table 1 Details of Parametric Study
SS.N PARAMETER VALUE
11 Diameter of Pile (D) 20 cm
22 Width of footing (B) 1.5 m
33 Slope Inclination 1:2
44 d/B ratio 0
55 L/B ratio 3, 4, 5, 8, 10
66 Location of pile from crest (d) 0X, 0.2X, 0.4X, 0.6X, 0.8X
77 Inclination of pile 0º
, 10º
, 20º
, 30º
88 Width of load 2m, 4m, 8m, 16m
The slope model along with pile and footing used for analysis is as shown in
Figure.1. The slope modeled in PLAXIS 2D for one condition is shown in Figure. 2.
Figure 1 Pile-Stabilized slope

Figure 2 Model Geometry in Plaxis 2D
MATERIAL PROPERTIES
The properties of soil used in slope, strip footing and pile are given in Table 2, Table
3 and Table 4 respectively. These properties are used for PLAXIS 2D analysis.
Table 2 Soil Properties
Sr. No Parameter Value
1 Type of material Sand
2 Material Model Mohr - Coulomb
3
4
Young’s modulus of sand(kN/m2
) 50000
4 Cohesion (kN/m2
) 0.5
5 Poisson’s ratio 0.30
6 Friction angle(Φ) 34°
7 Interface reduction factor Rinter 0.67
8 Dry density(kN/m3
) 18

Table 3 Strip footing properties
1 Type of material Elastic
2 Normal stiffness, EA (kN/m) 30000000
3 Flexural rigidity, EI (kN/m2
/m) 25000
Table 4 Pile Properties
1 Type of material Elastic
2 Normal stiffness, EA (kN/m) 2.826E06
3 Flexural rigidity, EI (kN/m2
/m) 7065
REULTS AND DISSCUSSION
The analysis was carried out using PLAXIS 2D for slope with strip footing and piles.
The numbers of piles per meter length were considered for the analysis and equivalent
normal stiffness (EA) and bending stiffness (EI) were calculated accordingly. The pile
was modeled as a plate element of equivalent stiffness to consider it as plain strain
problem for analysis. The results of analysis for different parameters affecting the
performance of reinforced slope using piles are discussed with respect to bearing
capacity, factor of safety and width of strip load.
Factor of Safety of Slope
The effect of pile length, pile inclination and pile location on factor of safety (FOS) of
slope was studied for a load which results in failure of load without reinforcement i.e.
for FOS =1. The ultimate load obtained was divided by factor of safety 3 to determine
the safe load to be applied. For all analysis, this safe load was applied on slope and
the piles were used to improve factor of safety. The FOS value of unreinforced slope
was used to compare the results with pile-reinforced slope. The variation of FOS for
different L/B ratios with pile location and pile inclinations are shown in Fig. 3. It can
be seen that the factor of safety was maximum when the pile was located at crest of
slope for all L/B ratios and the pile reinforcement was observed to be effective up to
0.5X distance from crest i.e. at middle of slope.

Figure 3: Effect of Pile Location for Different L/B Ratios
(a) For L/b = 3
(b) For L/b = 5
(c) For L/b = 8

(d) For L/b = 10
Ultimate Bearing Capacity
The strip footing behavior in terms of ultimate bearing capacity (UBC) for different
parameters was studied. The maximum load just before failure was observed and a
load settlement curve was drawn for each case to determine the ultimate bearing
capacity of strip footing under vertical load. The ultimate bearing capacity of
unreinforced slope was used to compare the effectiveness of pile reinforcement. The
variation of UBC for different L/B ratios with pile location and pile inclinations is
shown in Fig. 4. The results indicate that the pile reinforcement had significance
effect on ultimate bearing capacity of the strip footing. The UBC was observed to
maximum when the pile was located at crest of slope for all the L/B ratios. For L/B of
3 to 5, 10⁰ inclined piles gives maximum value of UBC as compared to other piles
and for L/B ratio more than 8; vertical pile gives maximum value of UBC as
compared to all inclined piles.
Figure 4 Variation of UBC for Different L/B Ratios
(a) For L/b = 3

(b) For L/b = 4
(c) For L/b = 5
(d) For L/b = 8

(e) For L/b = 10
Effect of Load Width
The strip load width considered for the analysis was 2m, 4m, 8m and 16m. The strip
load was applied as uniformly distributed load on embankment. The effect of strip
load width was determined in terms of factor of safety of slope.
The variation of FOS for different length of piles with pile location and pile
inclinations for strip load width of 2m and 16m are shown in Fig. 5 and Fig. 6
respectively. The results indicate that for small load width of 2 m and 4 m, the
optimum location of pile at slope crest gave maximum factor of safety. There is
marginal increase in factor of safety of slope as length of pile increases. For strip
width more than 8m, the optimum location of pile which gave maximum factor of
safety was observed at the middle of the slope. The inclination of pile had marginal
effect on the factor of safety of slope.
Figure 5 Variation of FOS for Load Width 2 M
(a) For Lp = 3m
5

(b) For Lp = 6m
(c) For Lp = 10m
(d) For Lp = 15m

Figure 6: Variation of FOS for Load Width 16 M
(a) For Lp = 3m
(b) For Lp = 6m (c) For Lp = 3m
(d) For Lp = 6m

CONCLUSIONS
The analysis of pile reinforced slope had been carried using PLAXIS 2D to evaluate
the effect of strip footing on performance of pile reinforced slope in terms of factor of
safety and / or ultimate bearing capacity. The piles installed within the slope,
mechanically provides a resistance to slope system along the failure surface. The main
aim of this study was to investigate the effect of pile location from crest, pile length,
pile inclination and width of strip load. From this study the following conclusions
were drawn:
 Pile reinforcement had significant effect on the performance of slope with strip
footing on embankment.
 The maximum UBC was observed when the pile was located at crest of slope for all
the L/B ratios.
 For smaller L/B ratios up to 5, 10 degree pile inclination gave maximum bearing
capacity and for higher L/B ratio vertical pile gives maximum bearing capacity as
compared to inclined piles.
 The optimum pile location which gave maximum value of factor of safety was
observed to be at crest of slope for all L/B ratios.
 As strip load width increases, the optimum pile location was observed to be at middle
of slope for higher values of L/B as compared to small strip load width.
REFERENCES
[1] Cai F. and Ugai K. (2000), Numerical Analysis of the Stability of a Slope
Reinforced with Piles, Soils and Foundation, 40, pp.73–84.
[2] Gullu H. (2013), A Numerical Study on Pile Application for Slope Stability, 2nd
International Balkans Conference on Challenges of Civil Engineering, BCCCE,
Epoka University, Tirana, Albania, pp. 810–816.
[3] Won J., You K., Jeong S. and Kim S. (2005), Coupled Effects in Stability
Analysis of Pile–Slope Systems, Computers and Geotechnics, 32, pp. 304–315.
[4] Wang L. and Zhang G. (2013), Pile-Reinforcement Behaviour of Cohesive Soil
Slopes: Numerical Modeling and Centrifuge Testing, Journal of Applied
Mathematics.
[5] Yang S., Ren X. and Zhang J. (2011), Study on Embedded Length of Piles for
Slope Reinforced with one Row of Piles, Journal of Rock Mechanics and
Geotechnical Engineering, 3(2), pp. 167–178.
[6] Anuj Chandiwala, FEM Modeling for Piled Raft Foundation in Sand,
International Journal of Civil Engineering and Technology, 4(6), 2014, pp. 239–
251.
[7] Sunil S. Pusadkar and Sachin N. Ghormode, Uplift Capacity of Piles in Two
Layered Soil, International Journal of Civil Engineering and Technology, 6 (3),
2015, pp. 132–138.

PERFORMANCE OF STRIP FOOTINGS ON SLOPE REINFORCED WITH INCLINED PILE

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à PERFORMANCE OF STRIP FOOTINGS ON SLOPE REINFORCED WITH INCLINED PILE

Similaire à PERFORMANCE OF STRIP FOOTINGS ON SLOPE REINFORCED WITH INCLINED PILE (20)

Plus de IAEME Publication

Plus de IAEME Publication (20)

Dernier

Dernier (20)

PERFORMANCE OF STRIP FOOTINGS ON SLOPE REINFORCED WITH INCLINED PILE