Indian Geotechnical Conference (IGC-2010)igs/ldh/files/igc 2015 pune... · Based on the soil...
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50
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INDIAN GEOTECHNICAL CONFERENCE
17th
– 19th
DECEMBER 2015, Pune, Maharashtra, India
Venue: College of Engineering (Estd. 1854), Pune, India
SITE CHARACTERIZATION AND BEARING CAPACITY ESTIMATION
FOR A SCHOOL BUILDING LOCATED ON HILLSLOPE R. Acharyya
1, A. Dey
2
ABSTRACT
Footings located on or near a slope (e.g. bridge piers on approach embankments, foundations of
transmission towers and buildings on the hill-slopes), the slope face acts as a finite boundary that leads to
an improper and limited development of the plastic region of failure as the foundation approaches the
limit state under the applied loading. Depending upon the location of the footing and steepness of the
slope, the above-mentioned phenomena might lead to substantial reduction in the bearing capacity of the
foundation. In addition, the presence of the unprotected face of the slope leads to noticeable outward
movement which in turn can lead to ominous settlement failure of the foundation. There exists a
significant lack of knowledge in estimating the bearing capacity predictions for footing on slopes.
North-eastern regions of India is experiencing massive outgrowth in the number of habitations leading to
widespread construction of residential and commercial buildings due to increasing urbanization. Majority
part of the terrain being covered by hills, the upcoming construction activities are either directly situated
on the hill slopes or on the artificially prepared terraces. For buildings, a common scenario which is
encountered with relation to foundations is that individual footings of the buildings are often located at
different levels and different depths of the embedment when placed on slope faces. In these conditions, it
is extremely necessary to understand the behavior of the soil under such multiple loading conditions,
since, based on the soil and loading characteristics, the originally stable slope faces might become
vulnerable to failure and may lead to a deformation based failure of the structure. It is utterly necessary to
identify the failure mechanism in such conditions, so that proper protective measures can be adopted if
the situation arises. Such failure mechanisms does not follow the conventional bearing capacity failure
theories developed for semi-infinite soil medium, and should be dealt with caution and intricacy.
This article reports about a detailed soil characterization conducted for a site at Teli, Arunachal Pradesh
which would be used to construct a school building resting on hill-slope. The foundation mostly
1Acharyya_Rana, Department of Civil Engineering, IIT Guwahati, Guwahati, India, [email protected]
2Dey_Arindam, Department of Civil Engineering, IIT Guwahati, Guwahati, India, [email protected]
R. Acharyya, A. Dey
comprises of isolated square footings located at different levels of embedment. The soil at the site is
observed to be mostly sandy with the presence of fine content. The soil also contains weathered rock
fragments composed of micaceous flakes. Disturbed soil from the site has been collected from three
different locations and an extensive laboratory investigation has been carried out to identify the important
physical and engineering properties of the same. Laboratory investigations namely specific gravity,
particle size distribution (dry sieve, wet sieve and hydrometer), Atterberg limits, free swell potential,
consolidation and consolidated drained triaxial tests have been carried out. Soils collected from different
locations, upon testing, indicated the stratum to be fairly homogeneous. Shear strength parameters
estimated from the tests have been used to evaluate the ultimate bearing capacity of the footings with
proper consideration of their locations on the slope face with theoretical and numerical analysis (PLAXIS
3D v2012) and comparison has been made of both analysis.
Keywords: Foundations on slopes, Soil characterization, Bearing Capacity, PLAXIS 3D
50
th
IG
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50th
INDIAN GEOTECHNICAL CONFERENCE
17th
– 19th
DECEMBER 2015, Pune, Maharashtra, India
Venue: College of Engineering (Estd. 1854), Pune, India
SITE CHARACTERIZATION AND BEARING CAPACITY ESTIMATION
FOR A SCHOOL BUILDING LOCATED ON HILLSLOPE
Acharyya, R., Research Scholar, Department of Civil Engineering, IIT Guwahati, [email protected].
Dey, A.*, Assistant Professor, Department of Civil Engineering, IIT Guwahati, [email protected].
ABSTRACT: Buildings in North-Eastern India are commonly built on shallow foundations without any proper
geotechnical characterization of the underlying soil. This paper reports about a thorough geotechnical investigation
attempted for a site at Teli, Arunachal Pradesh, where a monastery school building is to be built on the slope face
of a hill. Soil samples have been collected from the site and several laboratory investigations have been carried out.
Based on the soil properties, both theoretical analysis and numerical simulations have been carried out to estimate
the bearing capacity and explore the deformation mechanisms of a single isolated footing.
INTRODUCTION
The ultimate bearing capacity of shallow
foundation placed near or on the slope has been a
matter of concern for the foundation engineers for
a long time. Foundations are sometimes located on
the faces of the slopes or near the edges of slopes.
Examples of such practice are buildings or roads
constructed in hilly regions, electric transmission
towers built on mountain slopes, and foundations
for bridge abutments resting on granular fill slopes.
The bearing capacity of a foundation constructed
near the edge of a slope assumes its importance in
view of the fact that performance of the structure
and the bearing capacity primarily depends on the
stability of the slope. Alike to the foundations
resting on horizontal ground surface, a shallow
footing in a slope can also be subjected to a variety
of loading (axial, inclined, eccentric, coupled
moments or their combinations). However, in
contrary to the former, the response of footings on
slopes becomes more critical due to a noticeable
reduction in ultimate bearing capacity [1, 2, 3].
This is primarily attributed to the incomplete
development of the passive zone near the slope
face where there is not enough lateral restraint on
the soil to resist it outward lateral movement
resulting in substantial reduction in the bearing
capacity and ominous outward deformation of the
foundation. Although the issue is of major
significance, experimental studies related to the
behaviour of footings on slopes are rather limited.
Majority of the experimental investigations [2, 3, 4,
5, 6) have been conducted in the laboratory on dry
cohesionless sandy soil with the objective of
estimating the ultimate bearing capacity and the
associated bearing capacity factor (Nγq) while
studying the effect of various influencing
parameters (e.g. setback distance, width of the
footing, relative density of slope material,
steepness of the slope and type of loading on the
footing) on the bearing capacity reduction factor.
Except for very few tests conducted on square
footings resting on the crest of the slope, [5], all the
above-mentioned experimental investigations have
been conducted on strip footings. The results of the
investigations conducted on a skirted strip footing
resting on the crest of sandy slope have been
reported in [7]. Apart from laboratory
investigations, meagre numbers of field
measurement related to the behaviour of anchored
inclined footings on a natural slope have been
reported in [8].
If the spread of habitation in the North-Eastern
(NE) regions of India are glimpsed, one can easily
recognize the locations to be primarily on
unreinforced hill-slopes or terraces of the same
(Photograph 1). With the passage of time, growing
inhabitation and changing trends of the building
structures (from light-weight Assam-type housing
to multi-storied concrete structures) is gradually
appending to changing deformation and instability
R. Acharyya, A. Dey
of the slopes because of inadequate design of the
foundation resting on or near the slope.
Photograph 1 Residential habitation on the hill-
slopes of Bomdila, Arunachal Pradesh
The present investigation has been carried out with
disturbed soil samples collected from the site at
Teli, Arunachal Pradesh. The soil has been
collected from three different locations and an
extensive laboratory investigation has been carried
out to identify the important physical and
engineering properties of the same. Strength and
stiffness parameters estimated from the tests have
been used to evaluate the bearing capacity of the
footings with proper consideration of their
locations on the slope face. Numerical FE
modelling has been done with PLAXIS 3D v2012
to validate the bearing capacity that has been
obtained from the theoretical analysis and make an
introspective study of the involved deformation
mechanisms.
EXPERIMENTAL INVESTIGATION AND
SOIL CHARACTERISATION
Detailed laboratory experiments have been
conducted to characterise the soils collected from
two different locations at the project site (L1 and
L2), as exhibited in Photograph 2. Two soil
samples (S1 and S2), at depths of 1 m and 1.5 m
respectively from the ground surface, have been
collected from Location 1. The third soil sample
(S3) was collected from a depth of 1 m below the
ground level at Location 2. Various laboratory tests
have been conducted on the soils samples for the
determination of specific gravity, Atterberg limits
(Liquid limit, Plastic limit and Shrinkage limit),
free swell index, particle size distribution,
compaction characteristics, shear strength
characteristics and consolidation characteristics. A
briefing of the conducted experiments is provided
in the subsequent sections.
Photograph 2 Shallow foundations being laid for a
school building on slope at Teli, Arunachal
Pradesh
Specific Gravity
As per [9]¸ specific gravity of each sample was
determined using a specific gravity bottle by taking
10 gm of oven dried soil sample passing through
4.75 mm sieve.
Atterberg Limits
Liquid Limit and Plastic Limit
As per [10]¸ liquid limit (LL) determination was
conducted with the aid of Casagrande apparatus by
taking 120 gm of oven dried soil sample passing
through 425 µm sieve.
As per [10]¸ plastic limit (PL) was determined for a
soil sample by making thread of 3 mm diameter
with the oven dried soil sample of 8 gm mixed with
appropriate water content.
Shrinkage Limit
As per [11], shrinkage limit of 30 gm soil sample
was evaluated using the mercury displacement
method.
L1
L2
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INDIAN GEOTECHNICAL CONFERENCE
17th
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DECEMBER 2015, Pune, Maharashtra, India
Venue: College of Engineering (Estd. 1854), Pune, India
Free Swell Index
As per [12], the free swell index was obtained for
oven dried soil sample passing through 425µm
sieve. Soil sample of 10 gm was poured in each of
the two graduated glass cylinders of 100 ml
capacity. One cylinder was then filled with
kerosene oil and the other with distilled water up to
the 100 ml mark. The volume of soil was checked
after 24 hours to identify the amount of expansion
in volume.
Sieve Analysis
Since the collected soil sample possessed a visually
significant fine content, as per [13], wet sieve
analysis has been done for each soil sample. Oven
dried soil sample of 500 gm was taken and washed
over 75 µm sieve under flowing tap water until the
clean water was observed to be passing from the
sieve. The soil retained on 75µm sieve was oven
dried and sieved through the set of IS sieves 4.75
mm, 2.80 mm, 2 mm, 1 mm, 600 µm, 425 µm, 300
µm, 150 µm, and 75 µm. based on the obtained
particle size distribution (PSD), the coefficient of
curvature (Cc) and coefficient of uniformity (Cu)
were calculated.
Hydrometer Analysis
As per [13], hydrometer analysis was performed
with 50 gm oven dried soil sample passing through
75µm sieve. Sodium hexametaphosphate solution
was used as a dispersing agent and soil was
thoroughly mixed. Hydrometer and thermometer
were used as the specified time to take the readings
for the corresponding mix density and the
temperature of the suspension. The particle size
distribution of the finer fraction has been
estimated.
Proctor Compaction
As per [14], standard proctor compaction test was
carried out using 2.5 kg oven dried soil sample
passing through 4.75 mm sieve. Proctor mould was
filled with soil mixed with desired water content in
three layers and each layer was compacted by 25
blows of a 2.6 kg rammer falling from 310 mm
height. The optimum moisture content (OMC) and
maximum dry density (MDD) is determined from
the test.
Unconfined Compressive Strength
As per [15], unconfined compressive strength
(UCS) of soil was determined using oven dried soil
sample passing through 4.75 mm sieve. Cylindrical
soil sample of 38 mm diameter and 76 mm height
was formed with optimum moisture content and
maximum dry density of soil obtained from Proctor
compaction and was subjected to compression in
the absence of any applied confining pressure.
Triaxial Shear Test
As per [16, 17], unconsolidated undrained (UU),
consolidated undrained (CU), and consolidated
drained (CD) triaxial shear tests were performed on
cylindrical soil (passing through 4.75 mm sieve)
samples of 38 mm diameter and 76 mm height
formed with optimum moisture content and
maximum dry density. Although the codes suggest
saturating the soil samples, in the present study the
tests were performed with soil sample formed with
optimum moisture content and maximum dry
density to get shear strength parameters of soil in
actual field condition.
Oedometer Test
As per [18], oedometer Test was performed to
evaluate the consolidation characteristics of oven
dried soil sample passing through 4.75 mm sieve.
The sample of 60 mm diameter and 2 mm height
was prepared in its OMC-MDD condition. The test
was continued using a loading sequence of
successively increasing applied stresses (20, 50,
100, 200, 400, 800 kN/m2) on the soil specimen.
The settlement under each loading stage was
observed in a specified time sequence (0, 1/4, ½, 1,
2, 4, 8, 15, 30, 60 min and 2, 4, 8, 24 hr).
Results and Discussions
The engineering properties and shear strength
properties of the soil samples tested in the
laboratory have been tabulated in Table 1 and
Table 2, respectively. It was found during the
R. Acharyya, A. Dey
evaluation of Atterberg limits that formation of 3
mm thread for PL determination was difficult, as
the micaceous elements present in all the samples
resulted in premature crumbling of the specimens
without allowing the formation of threads.
Table 1 Engineering properties of soil samples Properties Soil type
S1 & S2 S3
Specific gravity 2.71 2.61
Particle size distribution
Sand (%) 60 44
Silt (%) 28 42
Clay (%) 12 14
Coefficient of curvature 0.76 0.85
Coefficient of uniformity 3.67 4.70
Atterberg Limits
LL (%) 44.9 44.9
PL (%) - -
SL (%) 23.80 23.80
Free swell index (%) 10 10
Compaction characteristics
OMC (%) 17.7 17.4
MDD (gm/cc) 1.87 1.77
Consolidation characteristics
Compression index Cc 0.093 0.1096
Swelling index Cs 0.039 0.0374
Preconsolidation stress 90 100.5
Table 2 Shear strength properties of soil samples
Properties Value
UCS (kPa) 178.24
Cohesion c (kPa)
UU 12
CU 0
CD 7.8 Angle of internal friction φ (degree)
UU 43
CU 44 CD 45
Figures 1 and 2 reveal the particle size distribution
of the specimens collected. Soil samples S1 and S2
exhibit nearly identical characteristics, ad hence,
only one curve is shown for both the samples. The
curves show that the soils were nearly same in
composition. It is observed from the coefficients of
uniformity and curvature, as well as from Figure 1,
that the soil samples are nearly well-graded.
Presence of fines as observed from the particle size
distribution of the coarser and finer fractions
indicate that it is a c-φ soil.
Figure 1 Particle size distribution of coarser
fraction obtained from wet sieve analysis
Figure 2 Particle size distribution of finer fraction
obtained from hydrometer analysis
Figure 3 exhibits the compaction characteristics of
the soil samples which is found to be nearly
similar, the magnitude of which are mentioned in
Table 1. It can be observed that although the
compaction curves of the samples showed a
deviation in their dry of optimum state, the OMC-
MDD states obtained are nearly the same. The
deviation can be attributed to the discrepancy in
preparation of the sample using low water content.
Figures 4-8 depict the consolidation characteristics
of the soil samples. Figure 4 depicts a typical
e-log p curve obtained from the consolidation test.
The plot have been used to estimate the
compression index (Cc), swelling index (Cs), and
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INDIAN GEOTECHNICAL CONFERENCE
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Venue: College of Engineering (Estd. 1854), Pune, India
the preconsolidation pressure (pc) of the soil
samples. The virgin- or the field-compression
curve has also been identified from the same.
These parameters can primarily be used to model
the constitutive behaviour of the soil in any
numerical analysis, as well as for the simplistic and
crude estimation of settlements which might take
place at the site. The magnitudes of the above-
mentioned parameters are mentioned in Table 1,
which shows that the soil samples do not differ
considerably from each other.
Figure 3 Compaction characteristics from
Standard Proctor compaction test
Figure 4 Typical e-log p curve obtained from
oedometer test for soil sample S1
The variation of coefficient of permeability (k)
with stress has been presented in Figure 5 and it is
revealed that the coefficient of permeability
becomes asymptotic beyond an applied stress of
500 kPa. Figure 6 exhibits that the coefficient of
consolidation (Cv) varies with applied stress. Cv is
observed to increase up to an applied stress of 200
kPa, beyond which it decreases and tends towards
an asymptote. Figure 7 and 8 depicts that the
coefficient of compressibility (av) and coefficient
of the volume compressibility (mv) decreases with
the increase in applied stress which is primarily
attributed to the decrease in void ratio with
progressive consolidation of the sample.
Figure 5 Variation of k with applied stress
Figure 6 Variation of Cv with applied stress
Figure 9 shows the comparative p-q plot obtained
from the stress-strain characteristics of various
triaxial tests (UU, CU, CD), which have been used
to estimate the shear strength characteristics of the
soil (as mentioned in Table 2). Based on the
obtained compaction characteristics, the triaxial
tests were carried out by preparing soil specimens
R. Acharyya, A. Dey
with MDD and its corresponding OMC. It is
observed that all the three tests result in nearly
identical shear strength parameters.
Figure 7 Variation of av with applied stress
Figure 8 Coefficient of mv with applied stress
Figure 9 Comparative p-q plot for triaxial tests
The above section presents a first-ever complete
geotechnical characterization of the soil at project
site at Teli, Tawang, Arunachal Pradesh. Based on
the above findings, it can be stated that for the site
in consideration, the engineering characteristics of
the soil samples collected from different locations
does not vary by a significant amount. Hence, the
soil at the site can be considered to be nearly
homogeneous. The estimated magnitudes of the
parameters will be further used to define the soil
properties for numerical modelling as well as the
estimation of the bearing capacity by analytical
methods.
BEARING CAPACITY ESTIMATION BY
ANALYTICAL METHOD
Meyerhof’s bearing capacity equation and chart for
bearing capacity factors [19, 20] have been used
for evaluating the ultimate bearing capacity of
shallow square footing of 2 m width resting on flat
ground surface, slope crest and sloping ground
surface. Ultimate bearing capacity (qu) of a 2 m
wide square footing has been calculated using the
shear strength parameters obtained from CD test.
The bearing capacity equations for square footing
resting on horizontal ground and slope are
respectively given as:
0.4u c f qq cN D N BN (1)
0.4u cq qq cN BN (2)
where, Df is the footing embedment depth, B is the
width of footing, γ is the unit weight of soil (MDD
as obtained from Proctor test). Nc, Nq, and Nγ are
Meyerhof’s bearing capacity factor for footing
resting on horizontal ground surface, while Ncq and
Nγq are Meyerhof’s resultant bearing capacity
factors for footing resting on a slope. qu has been
estimated for footings at various locations which
are elaborated in the following section and the
estimated magnitudes are provided in Table 6.
NUMERICAL FE MODELLING
Brief Overview of PLAXIS 3D
PLAXIS 3D is a finite element package intended
for three-dimensional analysis of deformation,
stability and ground water flow in geotechnical
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INDIAN GEOTECHNICAL CONFERENCE
17th
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DECEMBER 2015, Pune, Maharashtra, India
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engineering. Geotechnical applications require
advanced constitutive models for simulations of
non-linear, time-dependent and anisotropic
behaviour of soil or rock. Moreover, since the soil
is multi-phase material, special procedures are
required to deal with hydrostatic and non-
hydrostatic pore pressure in soil. Many
geotechnical projects involve the modelling of
structures and the interaction between structures
and the soil. PLAXIS 3D is equipped with features
to deal with various aspects of complex
geotechnical structures.
Model Details and Description
Geometry
In the present study, two types of model geometry
have been used. One of the model geometry (G1)
has been formed by considering footing on
horizontal ground surface or footing below
horizontal ground surface (Figure 10). The other
model geometry (G2) has been formed by
considering footing on slope crest or footing on
slope face (Figure 11). The geometry details are
tabulated in Table 3. The dimensions of the models
have been chosen in such a way that the ‘0.1q’
stress contour (q is the stress applied by the
footing’ should not be intersected by the side and
bottom edges of the model.
Table 3 Model geometry details Model
description
Breadth
(m)
Length
(m)
Height
(m)
Slope
angle (β°)
G1 14 14 12 0
G2 14 31.79 12 34
In the present study, horizontal fixity was given to
the four vertical edges of the model. In the bottom
edge of the model, both vertical and horizontal
fixity were applied as the bottom is assumed to be
non-yielding. This boundary condition is referred
as the “standard fixity” in the software (Typically
shown for model G2 in Figure 12).
Meshing and Convergence
To perform finite element calculation, the model
was discretized into smaller finite number of
tetrahedral elements. The basic soil elements of 3D
finite element mesh are the 10-noded tetrahedral
elements. PLAXIS 3D program allows for a fully
automatic generation of finite element meshes. In
PLAXIS 3D, five types meshing is available like
very coarse, coarse, medium, fine, and very fine.
Typical meshing for model G2 has been shown in
Figure 13.
Figure 10 Footing on horizontal ground (G1)
Figure 11 Footing on sloping ground (G2)
The mesh should be sufficiently fine to obtain
accurate numerical results. On the other hand, very
fine meshes should be avoided since it will take
excessive time for calculations. A convergence
study has been done with typical footing location
for five different meshing (represented by their
average element length) to understand the effect of
mesh refinement on the obtained results. Figure 14
exhibits that beyond a medium mesh, the obtained
R. Acharyya, A. Dey
results are nearly identical in all practical
considerations. Hence, all the further studies are
conducted considering a medium mesh having a
non-dimensional average element size (0.036).
Figure 12 Typical boundary conditions for G2
Figure 13 Typical meshing adopted in PLAXIS
3D
Material Model
The soil is modelled by the linear elastic perfectly-
plastic Mohr-Coulomb (M-C) model which
involves five input parameters, i.e. elastic
parameters (stiffness E and Poisson’s ratio ν) and
strength parameter (φ and c for soil plasticity and ψ
as an angle of dilatancy). The soil properties for the
M-C model have been tabulated in Table 4.
Table 4 Soil properties E (kPa) ν c (kPa) φ (°) ψ (°) γ (kN/m
3)
40104
0.3
7.67
45
0
18.7
Table 5 Footing properties Modulus of
elasticity
(E) (kPa)
Poisson's
ratio
(µ)
Unit weight
(γ) (kN/m3)
Thickness
(d) (m)
210 x 106
0.265
78
0.02
In the present study, the footing is represented by a
plate element modelled as a linear isotropic
material. The properties of pate have been
tabulated in Table 5.
Figure 14 Convergence study for a typical FE
model
Calculation Phases
The complete numerical analysis has been done in
three stages for all the models. In the first stage,
only the soil model was activated for generation of
in-situ stresses. In the second stage, the plate was
activated to represent the presence of constructed
footing. The column load was activated in the third
and final stage to assess the stress-deformation
conditions in the medium.
Footing Locations
Figure 15 Footing locations adopted for analysis
Figure 15 depicts the location of footings for which
the numerical analysis has been carried out to
estimate the bearing capacity in a numerical
framework. Different conditions have been
considered to represent surface and embedded
footings on horizontal (P1 and P2) and sloping (P3
and P4) ground, and a footing resting on the slope
face (P5) as well.
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INDIAN GEOTECHNICAL CONFERENCE
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MODELLING OUTCOMES
Ultimate Bearing Capacity from FE Modelling
Footings at any of the locations (as mentioned in
Figure 15) were subjected to a high applied stress
so that the system undergoes failure and the failure
load can be ascertained. The load at failure is
obtained as a fraction (given as ΣMstage in PLAXIS
3D) of the total applied load. At failure, the
maximum stress generated beneath the footing is
considered as the ultimate bearing stress.
Table 6 Comparison of ultimate bearing capacity
Footing
Location
Ultimate bearing capacity (qu) (MPa)
Analytical Numerical
P1 4.91 14
P2 9.12 26.9
P3 2.28 8.97
P4 4.69 15.9
P5 1.39 6.61
Figure 16 Representative pressure bulbs for
footing at various locations
Table 6 provides a comparison of the ultimate
bearing capacity obtained from analytical and
numerical methods for footings at various
locations. It is observed that the ultimate bearing
capacities obtained from numerical analysis are
consistently higher in comparison to the analytical
estimates. This is primarily attributed to the
inefficacy of the theoretical method to take into
account the effect of 3-D confinement generated
for footings under practical considerations. Figure
16 shows representative pressure bulb diagram
revealing the stress distribution beneath the
footings P3, P4 and P5. Pressure bulbs are
manifestation of isobars which join points of equal
pressure generated due to the loaded footing. The
shape of isobars, obtained by the application of
Boussinesq’s principle, is found to be smooth.
However, Figure 16 reveals that the stress
distribution beneath the footing resting in a c-φ soil
will be rather distorted, which is attributed due to
the inherent non-linearity in the medium.
CONCLUSION
This article reports about a detailed soil
characterization conducted for a site at Teli,
Arunachal Pradesh which would be used to
construct a school building resting on hill-slope.
Theoretical and the FE analyses have been
conducted to estimate the bearing capacity of
footings resting on horizontal ground surface and
on or near slopes. Based on the present study, the
following main conclusions are drawn:
The soil samples collected from locations
L1 and L2 are found to possess nearly
identical characteristics, and hence, the site
can be attributed to be nearly
homogeneous.
Convergence study conducted for the FE
analysis revealed that a medium meshing is
sufficient for the present problem to obtain
accurate results.
Since the extent of the site is large in
comparison to the footing dimensions, the
model dimensions for the numerical study
are determined based on the assessment that
the pressure contour (of 10 percent applied
stress) was not intersected by the sides of
the model.
It has been seen that the ultimate bearing
capacity of the foundation obtained from
the numerical technique is consistently
higher than that obtained from analytical
estimates, which is attributed to the inherent
assumptions behind the theoretical
calculations which does not take into
account the 3-D confinement effect at the
site.
R. Acharyya, A. Dey
REFERENCES
1. Meyerhof, G.G. (1957), The ultimate
bearing capacity of foundation on slopes,
Proceedings of 4th
international conference
on soil mechanics and foundation
engineering, I, 384-386.
2. Shields, D., Chandler, N. and Garnier, J.
(1990), Bearing capacity of foundation in
slopes, Journal of Geotechnical
Engineering, 116(3), 528-537.
3. Bauer, G.E., Shields, D.H., Scott, J.D. and
Gruspier, J.E. (1981), Bearing capacity of
footing in granular slope, Proceedings of
the 11th
International Conference on Soil
Mechanics and Foundation Engineering,
Balkema, Rotterdam, The Netherlands, 2,
33-36.
4. Kumar, S.V.A. and Ilamparuthi, K. (2009),
Response of footing on sand slopes,
Conference Proceeding of the Indian
Geotechnical Conference, 622–626.
5. Castelli, F. and Lentini, V. (2012),
Evaluation of the bearing capacity of
footings on slopes, International Journal of
Physical Modelling in Geotechnics, 129(3),
112-118.
6. Keskin, M. S. and Laman, M. (2012),
Model Studies of Bearing Capacity of Strip
Footing on Sand Slope, KSCE Journal of
Civil Engineering, 17(4), 699-711.
7. Azzam, W.R and Farouk, A. (2010),
Experimental and Numerical Studies of
Sand Slopes Loaded with Skirted Strip
Footing, Electronic Journal of
Geotechnical Engineering, 15, 795-812.
8. Clark, J. I. and Mckeown, S. (1988), Field
measurements of the behaviour of inclined
footings on a natural slope, Canadian
Geotechnical Journal, 25, 662–674.
9. IS 2720 (Part III/Section I):1980
(Reaffirmed 2002) Method of test for soils:
Determination of specific gravity: Fine
grained soils.
10. IS 2720 (Part V):1980 (Reaffirmed 2006)
Method of test for soils: Determination of
liquid and plastic limit.
11. IS 2720 (Part VI):1972 (Reaffirmed 2001)
Method of test for soils: Determination of
shrinkage factor.
12. IS 2720 (Part XL):1977 (Reaffirmed 2002)
Method of test for soils: Determination of
free swell index of soil.
13. IS 2720 (Part IV):1985 (Reaffirmed 2006)
Method of test for soils: Grain size
analysis.
14. IS 2720 (Part VII):1980 (Reaffirmed 2002)
Method of test for soils: Determination of
water content-dry density relation using
light compaction.
15. IS 2720 (Part X):1991 (Reaffirmed 2006)
Method of test for soils: Determination of
unconfined compressive strength
16. IS 2720 (Part XI):1993 (Reaffirmed 2002)
Method of test for soils: Determination of
shear strength parameters of a specimen
tested in unconsolidated undrained triaxial
compression without the measurement of
pore water pressure.
17. IS 2720 (Part XII):1981 (Reaffirmed 2002)
Method of test for soils: Determination of
shear strength parameters of a specimen
tested in consolidated undrained triaxial
compression with the measurement of pore
water pressure.
18. IS 2720 (Part XV):1965 (Reaffirmed 2002)
Method of test for soils: Determination of
consolidation properties.
19. Das, B. M. (2009), Shallow Foundations,
Taylor and Francis.
20. Arora, K. R. (2011), Soil Mechanics and
Foundation Engineering, Standard
Publishers and Distributors.