Expansive soils are highly susceptible to volumetric changes leading to rapid loss in the bearing

capacity of footings resting on them. Among several techniques available to treat expansive soils, lime or fly ash

stabilization gained prominence during the past few decades due to its abundance and adaptability. Chemical

stabilization is widely used to treat expansive soils as it develops base exchange and cementation processes between

clay particles.When expansive soils are treated with chemicals, it is essential to obtain the load-settlement response

of footing resting on stabilized ground. In this study, Finite Element Analysis is performed using the commercial

software, PLAXIS 2D, to obtain the load-settlement response of a strip footing resting on untreated and treated

expansive soil. The bearing capacity of strip footing resting on treated soil is found to be about 150% higher than

that of footing resting on untreated soil

B, Umashankar

K V N S, Raviteja

K, Ramu

R, Dayakar Babu

Research Archive of Indian Institute of Technology Hyderabad

  Proceedings of Indian Geotechnical Conference IGC-2014 December 18-20, 2014, Kakinada, India  BEARING CAPACITY OF A STRIP FOOTING RESTING ON TREATED AND UNTREATED SOILS   KVNS Raviteja, Research Scholar, Indian Institute of Technology Hyderabad, ce14resch01003@iith.ac.in B Umashankar, Asst. Professor, Indian Institute of Technology Hyderabad, buma@iith.ac.in K Ramu, Professor, UCEK-JNTU Kakinada, kramujntu@gmail.com R Dayakar Babu, Professor, KITS-Divili, baburd1108@hotmail.com   ABSTRACT: Expansive soils are highly susceptible to volumetric changes leading to rapid loss in the bearing capacity of footings resting on them. Among several techniques available to treat expansive soils, lime or fly ash stabilization gained prominence during the past few decades due to its abundance and adaptability. Chemical stabilization is widely used to treat expansive soils as it develops base exchange and cementation processes between clay particles.When expansive soils are treated with chemicals, it is essential to obtain the load-settlement response of footing resting on stabilized ground. In this study, Finite Element Analysis is performed using the commercial software, PLAXIS 2D, to obtain the load-settlement response of a strip footing resting on untreated and treated expansive soil. The bearing capacity of strip footing resting on treated soil is found to be about 150% higher than that of footing resting on untreated soil.   INTRODUCTION Untreated expansive soils are highly susceptible to volumetric changes with changes in moisture content leading to a rapid loss in the bearing capacityof footings resting on them. To overcome this, expansive soils have to be stabilised inorder to improve their properties. Although different methods like soil replacement, prewetting and moisture control, etc., are available to treat expansive soils, these methods have certain limitations like high hauling cost, non-availability of competent replacement material, and difficulty in adaptability and construction, etc.   Chemical stabilization is an effective and economical method to treat expansive soils. In this study, lime and fly ash are used to improve the strength and compressibility properties of expansive soil.   This paper compares the load-settlement response of a strip footing resting on untreated and treated ground. The numerical modelling is performed using a commercially available Finite Element Software – PLAXIS 2D (2013).The improvement in the limit bearing capacity of the footing is also proposed.  REVIEW OF LITERATURE  Selected Studies on Chemical Stabilization Using Lime and Fly ash Among several techniques adopted to overcome the problems posed by expansive soils, lime stabilization gained prominence due to its abundance and adaptability [Snethan (1979)] [1]. Petry and Armstrong (1989) proposed that chemical stabilization of expansive clays involves changing the physical and chemical environment within and surrounding the clay particles in such a way that the clay particles require less water to satisfy the static imbalance. This makes it difficult for water to move into and out of the system [2]. Cokca (2001) found that plasticity index and swell potential decrease with addition of fly ash. The fly ash addition greater than 20% is comparable to lime addition equal to 8% in terms of reducing the plasticity and the swell potential in the soil [3]. Kumar and Sharma (2004) observed that the free-swell index reduced to 50% with the addition of 20% of fly ash. In addition, the plasticity characteristics were also reduced [4]. White et al. (2005) reported that the strength gain in soil-fly ash mixtures is dependent on curing time, temperature, compaction energy, and compaction delay [5]. Ramu and Babu (2010) reported that fiber reinforced fly ash with cement as an additive   K V N S Raviteja, B Umashankar, K Ramu & R Dayakar Babu resulted in reduction of heave by about 84% compared to that of uncushioned soil [6]. According to Geliga et al. (2010), the shear strength of sample mixtures cured for 7 days decreased when the amount of fly ash was equal to 80% of the total weight of the mixture. Besides, 60% of fly ash and clay mixture (by weight) resulted in the highest value of axial stress of the sample [7]. According to Harichane et al. (2010), a significant increase in cohesion was observed with time for samples stabilized with 8% lime content. However, the addition of natural pozzolana resulted in only a marginal increase on cohesion and friction angle with time. The combination of 20% natural pozzolana+8% lime resulted in high increase in cohesion for 28 days curing period [8]. Ramdas et al. (2011) reported 10%-13% increase in the unconfined compressive strength with the addition of 25% fly ash, whereas addition of lime up to 4% resulted in 40%-60% increase in the unconfined compressive strength [9]. Pankaj et al. (2012) reported a significant improvement in the CBR value of expansive soil stabilized with lime and fly ash, leading to a decrease in the thickness of pavement by about 66% [10]. Hasan (2012) observed that fly ash equal to 15% was the optimum value leading to maximum increase in the cohesion of soil- fly ash mixtures. This value of cohesion increased with curing time up to 14 days. However, the addition of fly ash had an insignificant effect on the angle of shearing resistance of the mixture [11]. Bose (2012) observed that the maximum unconfined compressive strength was obtained at 20% fly ash when mixed clay sample, and further addition of fly ash was found to reduce the compressive strength [12].  Recent Studies on BearingCapacity of Footing Smith and Griffiths (1998) reported that the bearing capacity analyses are carried out using finite element method by a viscoplastic algorithm and the elastic- perfectly plastic Tresca yield criterion. The soil medium is discretized using iso-parametric plane-strain elements [13]. Esmaili and Hataf (2008) observed that the results from the finite element analysis show a reasonably good agreement with laboratory experimental results with a discrepancy of within 0 to 14% [14]. Loukidis et al. (2008) used the finite-element method to determine the collapse load of a rigid strip footing resting on a uniform layer of frictional soil subjected to inclined and eccentric loading. The soil was assumed to be elastic-perfectly plastic and follows the Mohr-Coulomb failure criterion [15]. Musso and Ferlisi (2009) analysed the behaviour of a model strip footing resting on a saturated soil and subjected to centric or eccentric vertical loading. Experimental tests carried out on a small-scale physical model were able to reproduce the effective stress levels equivalent to those existing in the prototype problems [16]. Keskin and Laman (2012) performed both finite element analysis and experimental studies on the bearing capacity of footings. They concluded thatthe ultimate bearing capacity values obtained from FEAwas only slightly greater than that obtained from the model tests [17]. Balunaini et al. (2012) proposed the settlement influence factors due to uniform circular load acting on finite two layer system and found thatthe factors are in good agreement with the factors proposed by Ueshita and Meyerhof based on theory of elasticity [18]. Kaya and Ornek (2013) reported that the numerical analyses using an elastoplastic hyperbolic model gave results that are close to physical model tests. However, the numerical models from their analyses were found to underestimate the test results [19].  PROBLEM DEFINITION A strip footing of width equal to 2m is resting on a treated ground. It is proposed to obtain the load-settlement response of the treated ground and compare the response with that of untreated ground. It is also proposed to obtain the improvement in the limit bearing capacity of the footing resting on treated and untreated.  METHODOLOGY  Experimental Analysis The strength parameters of the untreated expansive soil were determined using unconsolidated, undrained (UU) triaxial tests. The undrained shear strength was found to be equal to 54 kPa.  The experimental results obtained after treating the soil with lime (contents ranging from 0% to 12%) and fly ash (ranging from 0% to 25%) by weight were analysed. Based on the experimental study,   Bearing capacity of a strip footing resting on treated and untreated soils   expansive soil was found to have the maximum undrained shear strength when treated with lime and fly ash contents equal to 9% and 20%. The undrained shear strength of treated soil was found to be equal to 407kPa.  The limit bearing capacity values of the strip footing resting on untreated and treated soil were calculated from the bearing capacity equation, and were found to be equal to 555 kN/m2 and 1373 kN/m2, respectively.  RESULTS AND DISCUSSIONS  Finite Element Analysis Finite element analysis (FEM) was performed using the commercial software Plaxis 2D-(2013). Plane-strain conditions were assumed and the soil model was developed. The boundary distances were suitably chosen in order to simulate the semi-infinite extent of soil medium.25m x 25m sized model was found to have minimum influence of boundaries on the load-settlement response of the footing (Fig. 1).  25 m25 mSTRIP FOOTING2 mSOIL  Fig. 1 Schematic representation of soil and footing  A strip footing of width equal to 2m was placed on the soil surface exactly at the center of the soil model as shown in Fig.1.  The FE model has been configured with 15-noded triangular elements. Mohr-Coulombmaterial model was assumed to represent untreated and treated soil. The boundaries are laterally fixed on both sides, and fixed horizontally and vertically at the bottom boundary.  Table 1 gives the soil properties of untreated expansive soil used to determine the bearing capacity of the strip footing resting on the untreated ground.  Table 1 Untreated expansivesoil properties  S.No Property Value 1. Poisson’s Ratio (µ)  0.2 2. Modulus (E) 15000kPa 3. Unsatured unit weight  of soil 16 kN/m3 4. Saturated unit weight of soil 18 kN/m3  The geometry consisted of 12593 number of nodes and 1544 number of soil elements with an average element size of 0.6362 m.  Fig. 2 shows the settlement profile of untreated ground.  The Figure indicates that the maximum settlement was found just below the footing and the settlement decreases with depth. The limit bearing capacity of footing (per meter length) resting on untreated expansive soil was found to be 563kN/m2 which is in close agreement with the limit bearing capacity of footing calculated from bearing capacity equation.   Fig. 2 Settlement profile of untreated expansive soil for a prescribed rigid footing displacement equal to 200mm    K V N S Raviteja, B Umashankar, K Ramu & R Dayakar Babu Similar method was followed while simulating the model for treated Soil. The settlement profile and the corresponding load-settlement curve are shown in the figures below.  Table 2 Treated soil properties  S.No Property Value 1. Poisson’s Ratio (µ)  0.2 2. Modulus (E) 15000kPa 3. Unsatured Unit wt.  of Soil 16 kN/m3 4. Saturated Unit wt. of Soil 18 kN/m3  It was clear from Fig. 3 that the settlements are maximum just below the footing and reduced with increment in the depth. It was inferred that the bearing capacity (per meter length) for the untreated expansive soil was found to be 1408kN/m2 which was near to the bearing capacity value that was calculated from the experimental results. All the simulations were carried out in a very fine mesh for undrained condition and obtained results are compared with each other.    Fig. 3 Settlement profile of treated soil for a prescribed rigid footing displacement equal 200mm  Fig. 4 shows the load versus settlement of footing. As the settlement increases, the load on the footing increases and the load reach a constant value beyond a certain footing settlement. The bearing capacity of footing was found to increase to a greater extent when the expansive soil was treated with optimum percentages of lime and fly ash. In both the cases, the limit bearing capacity value obtained from the Finite Element analysis was found to be in a close agreement with values obtained from the theoretical bearing capacity equation.   Fig.4 Variation of load on the footing with settlement in the case of footing resting on untreated and treated soils  Table 3 Comparison of untreated and treated soil properties S.No Property Untreated Treated 1. Saturated unit weight (kN/m3) 18 18 2. Unsaturated unit weight (kN/m3) 16 16 3. Modulus (kPa) 15000 15000 4. Poison’s Ratio 0.2 0.49 5. Cohesion (kPa) 54 342 6. Friction Angle 0o 10o 7. UCS (kPa) 108 815 8. Shear Strength (kPa) 54 407 9. Limit load (per ‘m’) (kN/m2) {from bearing capacity equation}555 1373 10. Limit load (per ‘m’) (kN/m2) {from FEM}563 1408 12. Improvement in the bearing capacity of footing {based on FE analysis}150 %    Bearing capacity of a strip footing resting on treated and untreated soils   Table 3 gives all the soil properties including the limit bearing capacity values calculated from both FE analysis and from theoretical bearing capacity equation.  CONCLUSIONS • It was observed that the limit bearing capacity of footing on treated soil was about 2.5 times than that of footing on untreated soil.  • The bearing capacity of footing calculated from FE analysis are found to be in close agreement with that obtained using the theoretical bearing capacity equation.  REFERENCES [1] Snethen, D.R. (1979), An evaluation methodology for prediction and minimization of detrimental volume change of expansive soils in highway subgrades, Research report prepared for federal highway administration, Washington, 1. [2] Perty, T.M. and Armstrong, J.C.  (1989), Stabilization of expansive clay soils, Journal of Transportation Research Board, TRB-1219, 103-112. [3] Cokca, E. (2001), Use of class C fly ashes for the stabilization of an expansive soil, Journal of Geotechnical and Geoenvironmental Engineering, 127(7), 568 -273. [4] Kumar, B.R.P. and Sharma, R.S. (2004), Effect of fly ash on engineering properties of expansive soils, Journal of Geotechnical and Geoenvironmental Engineering, 130, 764–767.  [5] White, D. J., Harrington, D.  and Thomas, Z.  (2005), Fly ash soil stabilization for non- uniform subgrade soils, Engineering Properties and Construction Guidelines. Iowa Highway Research Board Report: IHRB Project TR-461; FHWA Project 4. [6] Ramu, K. and Babu, R.D. (2010), Use of DFR fly ash cushion in minimizing heave of expansive clay beds, Proceedings of Indian Geotechnical Conference – 2010, 587-590. [7] Geliga, E.A. and Ismail, D.S.A.  (2010), Geotechnical properties of fly ash and its application on soft soil stabilization, UNIMAS E-Journal of Civil Engineering, 1(2), 1-6. [8] Harichane, K., Ghrici, Md. and Kenai, S.  (2010), Effect of curing time on shear strength of cohesive soils stabilized with combination of lime and natural pozzolana, International Journal of Civil Engineering, 9(2), June 2011, 90-96. [9] Ramadas, T.L., Darga Kumar, N. and Yesuratnam, G. (2011), Geotechnical characteristics of three expansive soils treated with lime and fly ash, International Journal of Earth Sciences and Engineering, 4(6) SPL, October 2011, 46-49. [10] Pankaj, R.M., Nangare, P.B., Nagrale, S.D., Nalawade, R.D. and Chavhan, V.S. (2012), Black Cotton Soil Stabilization by using Admixtures, International Journal of Engineering and Innovative Technology (IJEIT), 1(5), May 2012. [11] Hasan, H.A. (2012), Effect of fly ash on geotechnical properties of expansive soil, Journal of Engineering and Development, 16(2), June, 306-316. [12] Bose, B. (2012), Geo-Engineering properties of expansive soil stabilized with fly ash, Electronic Journal of Geotechnical Engineering, 17, 1339-1353. [13] Smith, I.M. and Griffiths, D.V.  (1998), Programming the Finite Element Method, 3rd Ed., Wiley, Chichester, U.K. [14] Esmaili, D. and Hataf, N. (2008), Experimental land numerical investigation of ultimate load capacity of shell foundations on reinforced and unreinforced sand, Iranian Journal of Science and Technology, Transaction B, Engineering, 32, 491-500. [15] Loukidis, D., Chakraborty, T. and Salgado R. (2008), Bearing capacity of strip footings on purely frictional soil under eccentric and inclined loads. Canadian Geotechnical Journal, 45(6), 768–787. [16] Musso, A. and Ferlisi, S. (2009), Collapse of a model strip footing on dense sand under vertical eccentric loads. Geotechnical and Geological Engineering, 27(2), 265-279. [17] Keskinand, M.S., Laman, M. (2012), Model studies of bearing capacity of strip footing on   K V N S Raviteja, B Umashankar, K Ramu & R Dayakar Babu sand slope, KSCE Journal of Civil Engineering (2013) 17(4), 699-711. [18] Balunaini, U., Yugandhar, D. and Madhav, M.R (2012), Settlement due to uniform circular load: on finite two-layer system, Journal of Geotechnical and Geological Engineering, 24. [19] Kaya, N. and Ornek, M. (2013), Experimental and numerical studies of T-shaped footings, ACT Geotechnica Slovenica, 143-58.            

Bearing Capacity of A Strip Footing Resting On Treated And

Untreated Soils

Expansive soils are highly susceptible to volumetric changes leading to rapid loss in the bearing\ud
capacity of footings resting on them. Among several techniques available to treat expansive soils, lime or fly ash\ud
stabilization gained prominence during the past few decades due to its abundance and adaptability. Chemical\ud
stabilization is widely used to treat expansive soils as it develops base exchange and cementation processes between\ud
clay particles.When expansive soils are treated with chemicals, it is essential to obtain the load-settlement response\ud
of footing resting on stabilized ground. In this study, Finite Element Analysis is performed using the commercial\ud
software, PLAXIS 2D, to obtain the load-settlement response of a strip footing resting on untreated and treated\ud
expansive soil. The bearing capacity of strip footing resting on treated soil is found to be about 150% higher than\ud
that of footing resting on untreated soil

KVNS, Raviteja

Balunaini, U

Name not available

 
 
Proceedings of Indian Geotechnical Conference IGC-2014 
December 18-20, 2014, Kakinada, India 
 
BEARING CAPACITY OF A STRIP FOOTING RESTING ON TREATED AND 
UNTREATED SOILS 
 
 
KVNS Raviteja, Research Scholar, Indian Institute of Technology Hyderabad, ce14resch01003@iith.ac.in 
B Umashankar, Asst. Professor, Indian Institute of Technology Hyderabad, buma@iith.ac.in 
K Ramu, Professor, UCEK-JNTU Kakinada, kramujntu@gmail.com 
R Dayakar Babu, Professor, KITS-Divili, baburd1108@hotmail.com 
 
 
ABSTRACT: Expansive soils are highly susceptible to volumetric changes leading to rapid loss in the bearing 
capacity of footings resting on them. Among several techniques available to treat expansive soils, lime or fly ash 
stabilization gained prominence during the past few decades due to its abundance and adaptability. Chemical 
stabilization is widely used to treat expansive soils as it develops base exchange and cementation processes between 
clay particles.When expansive soils are treated with chemicals, it is essential to obtain the load-settlement response 
of footing resting on stabilized ground. In this study, Finite Element Analysis is performed using the commercial 
software, PLAXIS 2D, to obtain the load-settlement response of a strip footing resting on untreated and treated 
expansive soil. The bearing capacity of strip footing resting on treated soil is found to be about 150% higher than 
that of footing resting on untreated soil. 
 
 
INTRODUCTION 
Untreated expansive soils are highly susceptible to 
volumetric changes with changes in moisture 
content leading to a rapid loss in the bearing 
capacityof footings resting on them. To overcome 
this, expansive soils have to be stabilised inorder to 
improve their properties. Although different 
methods like soil replacement, prewetting and 
moisture control, etc., are available to treat 
expansive soils, these methods have certain 
limitations like high hauling cost, non-availability 
of competent replacement material, and difficulty in 
adaptability and construction, etc.  
 
Chemical stabilization is an effective and 
economical method to treat expansive soils. In this 
study, lime and fly ash are used to improve the 
strength and compressibility properties of expansive 
soil.  
 
This paper compares the load-settlement response 
of a strip footing resting on untreated and treated 
ground. The numerical modelling is performed 
using a commercially available Finite Element 
Software – PLAXIS 2D (2013).The improvement in 
the limit bearing capacity of the footing is also 
proposed. 
 
REVIEW OF LITERATURE 
 
Selected Studies on Chemical Stabilization Using 
Lime and Fly ash 
Among several techniques adopted to overcome the 
problems posed by expansive soils, lime 
stabilization gained prominence due to its 
abundance and adaptability [Snethan (1979)] [1]. 
Petry and Armstrong (1989) proposed that chemical 
stabilization of expansive clays involves changing 
the physical and chemical environment within and 
surrounding the clay particles in such a way that the 
clay particles require less water to satisfy the static 
imbalance. This makes it difficult for water to move 
into and out of the system [2]. Cokca (2001) found 
that plasticity index and swell potential decrease 
with addition of fly ash. The fly ash addition greater 
than 20% is comparable to lime addition equal to 
8% in terms of reducing the plasticity and the swell 
potential in the soil [3]. Kumar and Sharma (2004) 
observed that the free-swell index reduced to 50% 
with the addition of 20% of fly ash. In addition, the 
plasticity characteristics were also reduced [4]. 
White et al. (2005) reported that the strength gain in 
soil-fly ash mixtures is dependent on curing time, 
temperature, compaction energy, and compaction 
delay [5]. Ramu and Babu (2010) reported that fiber 
reinforced fly ash with cement as an additive 
  
K V N S Raviteja, B Umashankar, K Ramu & R Dayakar Babu 
resulted in reduction of heave by about 84% 
compared to that of uncushioned soil [6]. According 
to Geliga et al. (2010), the shear strength of sample 
mixtures cured for 7 days decreased when the 
amount of fly ash was equal to 80% of the total 
weight of the mixture. Besides, 60% of fly ash and 
clay mixture (by weight) resulted in the highest 
value of axial stress of the sample [7]. According to 
Harichane et al. (2010), a significant increase in 
cohesion was observed with time for samples 
stabilized with 8% lime content. However, the 
addition of natural pozzolana resulted in only a 
marginal increase on cohesion and friction angle 
with time. The combination of 20% natural 
pozzolana+8% lime resulted in high increase in 
cohesion for 28 days curing period [8]. Ramdas et 
al. (2011) reported 10%-13% increase in the 
unconfined compressive strength with the addition 
of 25% fly ash, whereas addition of lime up to 4% 
resulted in 40%-60% increase in the unconfined 
compressive strength [9]. Pankaj et al. (2012) 
reported a significant improvement in the CBR 
value of expansive soil stabilized with lime and fly 
ash, leading to a decrease in the thickness of 
pavement by about 66% [10]. Hasan (2012) 
observed that fly ash equal to 15% was the optimum 
value leading to maximum increase in the cohesion 
of soil- fly ash mixtures. This value of cohesion 
increased with curing time up to 14 days. However, 
the addition of fly ash had an insignificant effect on 
the angle of shearing resistance of the mixture [11]. 
Bose (2012) observed that the maximum 
unconfined compressive strength was obtained at 
20% fly ash when mixed clay sample, and further 
addition of fly ash was found to reduce the 
compressive strength [12]. 
 
Recent Studies on BearingCapacity of Footing 
Smith and Griffiths (1998) reported that the bearing 
capacity analyses are carried out using finite 
element method by a viscoplastic algorithm and the 
elastic- perfectly plastic Tresca yield criterion. The 
soil medium is discretized using iso-parametric 
plane-strain elements [13]. Esmaili and Hataf 
(2008) observed that the results from the finite 
element analysis show a reasonably good agreement 
with laboratory experimental results with a 
discrepancy of within 0 to 14% [14]. Loukidis et al. 
(2008) used the finite-element method to determine 
the collapse load of a rigid strip footing resting on a 
uniform layer of frictional soil subjected to inclined 
and eccentric loading. The soil was assumed to be 
elastic-perfectly plastic and follows the Mohr-
Coulomb failure criterion [15]. Musso and Ferlisi 
(2009) analysed the behaviour of a model strip 
footing resting on a saturated soil and subjected to 
centric or eccentric vertical loading. Experimental 
tests carried out on a small-scale physical model 
were able to reproduce the effective stress levels 
equivalent to those existing in the prototype 
problems [16]. Keskin and Laman (2012) performed 
both finite element analysis and experimental 
studies on the bearing capacity of footings. They 
concluded thatthe ultimate bearing capacity values 
obtained from FEAwas only slightly greater than 
that obtained from the model tests [17]. Balunaini et 
al. (2012) proposed the settlement influence factors 
due to uniform circular load acting on finite two 
layer system and found thatthe factors are in good 
agreement with the factors proposed by Ueshita and 
Meyerhof based on theory of elasticity [18]. Kaya 
and Ornek (2013) reported that the numerical 
analyses using an elastoplastic hyperbolic model 
gave results that are close to physical model tests. 
However, the numerical models from their analyses 
were found to underestimate the test results [19]. 
 
PROBLEM DEFINITION 
A strip footing of width equal to 2m is resting on a 
treated ground. It is proposed to obtain the load-
settlement response of the treated ground and 
compare the response with that of untreated ground. 
It is also proposed to obtain the improvement in the 
limit bearing capacity of the footing resting on 
treated and untreated. 
 
METHODOLOGY 
 
Experimental Analysis 
The strength parameters of the untreated expansive 
soil were determined using unconsolidated, 
undrained (UU) triaxial tests. The undrained shear 
strength was found to be equal to 54 kPa. 
 
The experimental results obtained after treating the 
soil with lime (contents ranging from 0% to 12%) 
and fly ash (ranging from 0% to 25%) by weight 
were analysed. Based on the experimental study, 
  
Bearing capacity of a strip footing resting on treated and untreated soils 
 
 
expansive soil was found to have the maximum 
undrained shear strength when treated with lime and 
fly ash contents equal to 9% and 20%. The 
undrained shear strength of treated soil was found to 
be equal to 407kPa. 
 
The limit bearing capacity values of the strip footing 
resting on untreated and treated soil were calculated 
from the bearing capacity equation, and were found 
to be equal to 555 kN/m2 and 1373 kN/m2, 
respectively. 
 
RESULTS AND DISCUSSIONS 
 
Finite Element Analysis 
Finite element analysis (FEM) was performed using 
the commercial software Plaxis 2D-(2013). Plane-
strain conditions were assumed and the soil model 
was developed. The boundary distances were 
suitably chosen in order to simulate the semi-infinite 
extent of soil medium.25m x 25m sized model was 
found to have minimum influence of boundaries on 
the load-settlement response of the footing (Fig. 1).  
25 m
25
 m
STRIP 
FOOTING
2 m
SOIL 
 
Fig. 1 Schematic representation of soil and footing 
 
A strip footing of width equal to 2m was placed on 
the soil surface exactly at the center of the soil 
model as shown in Fig.1. 
 
The FE model has been configured with 15-noded 
triangular elements. Mohr-Coulombmaterial model 
was assumed to represent untreated and treated soil. 
The boundaries are laterally fixed on both sides, and 
fixed horizontally and vertically at the bottom 
boundary. 
 
Table 1 gives the soil properties of untreated 
expansive soil used to determine the bearing 
capacity of the strip footing resting on the untreated 
ground. 
 
Table 1 Untreated expansivesoil properties  
S.No Property Value 
1. Poisson’s Ratio (µ)  0.2 
2. Modulus (E) 15000kPa 
3. Unsatured unit weight  
of soil 
16 kN/m3 
4. Saturated unit weight 
of soil 
18 kN/m3 
 
The geometry consisted of 12593 number of nodes 
and 1544 number of soil elements with an average 
element size of 0.6362 m. 
 
Fig. 2 shows the settlement profile of untreated 
ground.  The Figure indicates that the maximum 
settlement was found just below the footing and the 
settlement decreases with depth. The limit bearing 
capacity of footing (per meter length) resting on 
untreated expansive soil was found to be 563kN/m2 
which is in close agreement with the limit bearing 
capacity of footing calculated from bearing capacity 
equation. 
 
 
Fig. 2 Settlement profile of untreated expansive 
soil for a prescribed rigid footing displacement 
equal to 200mm 
 
  
K V N S Raviteja, B Umashankar, K Ramu & R Dayakar Babu 
Similar method was followed while simulating the 
model for treated Soil. The settlement profile and 
the corresponding load-settlement curve are shown 
in the figures below. 
 
Table 2 Treated soil properties  
S.No Property Value 
1. Poisson’s Ratio (µ)  0.2 
2. Modulus (E) 15000kPa 
3. Unsatured Unit wt.  of 
Soil 
16 kN/m3 
4. Saturated Unit wt. of 
Soil 
18 kN/m3
 
 
It was clear from Fig. 3 that the settlements are 
maximum just below the footing and reduced with 
increment in the depth. It was inferred that the 
bearing capacity (per meter length) for the untreated 
expansive soil was found to be 1408kN/m2 which 
was near to the bearing capacity value that was 
calculated from the experimental results. All the 
simulations were carried out in a very fine mesh for 
undrained condition and obtained results are 
compared with each other. 
 
 
 
Fig. 3 Settlement profile of treated soil for a 
prescribed rigid footing displacement equal 
200mm 
 
Fig. 4 shows the load versus settlement of footing. 
As the settlement increases, the load on the footing 
increases and the load reach a constant value beyond 
a certain footing settlement. The bearing capacity of 
footing was found to increase to a greater extent 
when the expansive soil was treated with optimum 
percentages of lime and fly ash. In both the cases, 
the limit bearing capacity value obtained from the 
Finite Element analysis was found to be in a close 
agreement with values obtained from the theoretical 
bearing capacity equation. 
 
 
Fig.4 Variation of load on the footing with 
settlement in the case of footing resting on 
untreated and treated soils 
 
Table 3 Comparison of untreated and treated soil 
properties 
S.No Property Untreated Treated 
1. Saturated unit weight 
(kN/m3) 
18 18 
2. Unsaturated unit 
weight (kN/m3) 
16 16 
3. Modulus (kPa) 15000 15000 
4. Poison’s Ratio 0.2 0.49 
5. Cohesion (kPa) 54 342 
6. Friction Angle 0o 10o 
7. UCS (kPa) 108 815 
8. Shear Strength (kPa) 54 407 
9. Limit load (per ‘m’) 
(kN/m2) 
{from bearing capacity 
equation}
555 1373 
10. Limit load (per ‘m’) 
(kN/m2) 
{from FEM}
563 1408 
12. Improvement in the 
bearing capacity of 
footing 
{based on FE analysis}
150 % 
 
  
Bearing capacity of a strip footing resting on treated and untreated soils 
 
 
Table 3 gives all the soil properties including the 
limit bearing capacity values calculated from both 
FE analysis and from theoretical bearing capacity 
equation. 
 
CONCLUSIONS 
• It was observed that the limit bearing capacity of 
footing on treated soil was about 2.5 times than 
that of footing on untreated soil. 
 
• The bearing capacity of footing calculated from 
FE analysis are found to be in close agreement 
with that obtained using the theoretical bearing 
capacity equation. 
 
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Bearing Capacity of A Strip Footing Resting On Treated And\ud
Untreated Soils

http://raiith.iith.ac.in/1710/1/T07P21_Raviteja%20KVNS.pdf

Bearing Capacity of A Strip Footing Resting On Treated And Untreated Soils

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