Lateral response of pile foundations in lique fi able soils

Asskar Janalizadeh,Ali Zahmatkesh

Babol University of Technology,Babol,Iran

Full length article

Lateral response of pile foundations in lique fi able soils

Asskar Janalizadeh,Ali Zahmatkesh*

Babol University of Technology,Babol,Iran

A R T I C L E I N F O

Article history:

Received 6 March 2015

Received in revised form

5 May 2015

Accepted 6 May 2015

Available online 11 June 2015

Pile foundations Lateral spreading Liquefaction Pseudo-static method

Liquefaction has been a main cause of damage to civilengineering structures in seismically active areas. The effects of damage ofliquefaction on deep foundations are very destructive.Seismic behavior ofpile foundations is widely discussed by many researchers for safer and more economic design purposes.This paper presents a pseudo-static method for analysis of piles in lique fi able soil under seismic loads.A freefi eld site response analysis using three-dimensional(3D)numerical modeling was performed to determine kinematic loads from lateral ground displacements and inertial loads from vibration of the superstructure.The effects of various parameters,such as soil layering,kinematic and inertial forces, boundary condition of pile head and ground slope,on pile response were studied.By comparing the numerical results with the centrifuge test results,it can be concluded that the use of the p-y curves with various degradation factors in lique fi able sand gives reasonable results.

?2015 Institute of Rock and Soil Mechanics,Chinese Academy of Sciences.Production and hosting by Elsevier B.V.All rights reserved.

1.Introduction

The liquefaction is one of the challenging issues in geotechnical engineering and it damages structures and facilities during earthquakes.This phenomenon was reported as the main cause of damage to pile foundations during the major earthquakes(Kramer, 1996).In many earthquakes around the world,extensive damage to piles of bridges and other structures due to liquefaction and lateral spreading has been observed(Boulanger et al.,2003).Failures were observed in both sloping and level grounds and were often accompanied with settlement and tilting of the superstructure (Adhikari and Bhattacharya,2008).The loss of soil strength and stiffness due to excess pore pressure in lique fi able soilmay develop large bending moments and shear forces in the piles.If the residual strength of the lique fi able soil is less than the static shear stresses caused by a sloping site or a free surface such as a river bank,signi fi cant lateral spreading or downslope displacements may occur. The moving soil can exert damaging pressures against the piles, leading to failure(Finn and Fujita,2002).The performance of structures above piles depends widely on the behavior of pile foundations under earthquake loading.During past earthquakes, because of inadequacy of the pile to sustain large shear forces and bending moments,the extensive damage in lique fi able soil has been caused due to both lateral ground movement and inertial loads transmitted to piles.Under earthquake loading,the performance of piles in lique fi ed ground is a complex problem due to the effects ofprogressive buildup of pore water pressures and decrease ofstiffness in the saturated soil(Liyanapathirana and Poulos,2005). These effects involve inertialinteraction between structure and pile foundation,signi fi cant changes in stiffness and strength ofsoils due to increase of pore water pressures,large lateral loads on piles, kinematic interaction between piles and soils,nonlinear response of soils to strong earthquake motions,kinematic loads from lateral ground displacements,and inertial loads from vibration of the superstructure(Bradley et al.,2009;Gao et al.,2011).

Various approaches including shaking table and centrifuge tests and also various numerical methods have been developed for the dynamic response analysis of single pile and pile group.The soilpile-structure interaction has been investigated using the centrifuge test(e.g.Finn and Gohl,1987;Chang and Kutter,1989;Liu and Dobry,1995;Hushmand et al.,1998;Wilson,1998;Abdoun and Dobry,2002;Su and Li,2006)and shaking table test(e.g.Mizuno and Liba,1982;Yao et al.,2004;Tamura and Tokimatsu,2005; Han et al.,2007;Gao et al.,2011;Haeri et al.,2012).The obvious advantage of shaking table and centrifuge tests is the ability to obtain detailed measurements of response in a series of tests designed to physically evaluate the importance of varying earthquake characteristics(e.g.levelof shaking,frequency content),soil pro fi le characteristics,and/or pile-superstructure characteristics (Wilson,1998).However,some limitations exist in centrifuge tests, for example,sand grains in centrifuge tests correspond to bigger gravel particles in prototype(Towhata,2008).

To simulate the piles in lique fi able soil layers,Finn and Fujita (2002),Klar et al.(2004),Oka et al.(2004),Uzuoka et al.(2007),Cheng and Jeremic(2009),Comodromos et al.(2009),and Rahmani and Pak(2012)used three-dimensional(3D)fi nite element method.The complexity and time-consuming nature of 3D nonlinear fi nite element method for dynamic analysis makes it useful only for very large practical projects or research and not feasible for engineering practice.However,it is possible to obtain reasonable solutions for nonlinear response of pile foundations with fewer computations by relaxing some of the boundary conditions in full 3D analysis(Finn and Fujita,2002).

The simple approach for modeling and simulation of the piles in lique fi ed grounds is based on scaling of p-y springs,where p and y are the soil resistance per unit length of the pile and pile lateral displacement,respectively.Because of complexity and timeconsuming of two-dimensional(2D)and 3D numerical modeling, most of the designers and researchers prefer to use onedimensional(1D)Winkler method based on fi nite element or fi nite difference method for the seismic analysis ofpile foundations. In pseudo-static method,a static analysis is carried out to obtain the maximum response(de fl ection,shear force and bending moment) developed in the pile due to seismic loading.In Winkler models,p-y curves are used to de fi ne the behavior of the nonlinear spring at any depth.These p-y curves can be obtained from the results of model tests or fi eld(Liyanapathirana and Poulos,2005).The Winkler assumption is that the soil-pile interaction resistance at any depth is related to the pile shaft displacement at that depth only,independent of the interaction resistances above and below(Wilson, 1998).

This pseudo-static method has been suggested early by Miura et al.(1989),Miura and O’Rourke(1991),Liu and Dobry(1995), JRA(1996),AIJ(1998)and recently by Liyanapathirana and Poulos (2005)and Elahi et al.(2010).This method for pile seismic analysis sometimes underestimates,and sometimes overestimates shears,moments and de fl ection of the piles.However,in many practical conditions,the results of pseudo-static method are reasonable(Tabesh,1997).

In this paper,a pseudo-static method has been applied for estimation of the response of pile during dynamic loading.First,de finition of the geometry and the soil modeling parameters are presented.Next,the numerical model is verti fi ed by means of the centrifuge test.And then the effects ofvarious parameters,including soil layering,kinematic and inertial forces,boundary condition of pile head and ground slope,on the behaviors of piles are studied.

2.Numerical analysis

All simulations were conducted using the open-source computational platform OpenSees(McKenna and Fenves,2007).This platform allows for developing applications to simulate the performance ofstructuraland geotechnicalsystems subjected to static and seismic loadings.In this paper,the steps for calculation of pile response are summarized as follows:

(1)A free-fi eld site response analysis was performed during the dynamic loading using 3D numerical modeling.From this analysis,time history of ground surface acceleration and the maximumground displacement along the length ofthe pile can be calculated.

(2)The dynamic analysis was performed using the time history of ground surface acceleration calculated in Step 1 for pile length above ground and superstructure with a fi xed base.From this analysis,the maximum acceleration of superstructure can be calculated.

(3)In 1D Winkler analysis,the maximum soildisplacement pro fi le calculated in Step 1 and the maximum acceleration of superstructure in Step 2 were applied to the pile as shown in Fig.1.

First,the time history of the ground surface acceleration and the maximum ground displacement at each depth were obtained from the free-fi eld site response analysis.Taboada and Dobry(1993)and Gonzalez et al.(2002)showed that the pore pressure time histories recorded at the same elevation are identical,indicating the 1D behavior of the model.In free-fi eld analysis,the modelconsists ofa single column of 3D brick elements.The soil layers were modeled using cubic 8-noded elements with u-p formulation in which each node has four degrees of freedom:three for soil skeleton displacements and one for pore water pressure.To consider the effect of the laminar box in the numerical simulation,nodes at the same depths were constrained to have equal displacements in the horizontal and vertical directions.The pore water pressures were allowed to freely develop for all nodes except those at the surface and above the water table.The bottom boundary was assumed fi xed in all directions.

The materialmodel plays a key role in the numericalsimulation of the dynamic behavior of lique fi able soils.The model in Dafalias and Manzari(2004),a critical state two-surface plasticity model, was used in this paper.This model requires fi fteen material parameters and two state parameters to describe the behavior ofsands and has been amply tested for simulating the behavior of granular soils subjected to monotonic and cyclic loadings(Jeremic et al., 2008;Taiebat et al.,2010;Rahmaniand Pak,2012).The key advantages of the model are that(1)it is relatively simple and(2)it has a unique calibration of input parameters.Thus,a single set of parameters independent of void ratio and effective consolidation stress levelwas used for the Dafalias and Manzari’s materialmodel. Table 1 presents the material parameters for Nevada sand.The additional parameters used for free-fi eld analysis are presented in Table 2.Itcan be noted thatatthe onsetofliquefaction,change ofsoil particles creates additionalpathways for water.This leads to a signi fi cant increase in permeability coef fi cient(Rahmani et al.,2012). In this study,the permeability coef fi cient value was increased 10 times the initialvalue(suggested by Rahmani et al.(2012)).

For free-fi eld analysis,the simulations were carried out in two loading stages.At the fi rst stage,the soil skeleton and pore water weight were applied to soilelements.The values ofstress and strain in this stage were used as initialvalues for the next stage of loading. At the second stage,dynamic analysis was performed by application of an input motion to the model base.

Fig.1.A beam on the nonlinear Winkler foundation(BNWF)model for pseudo-static analysis.

Table 1 Materialparameters for Nevada sand(Rahmaniand Pak,2012).

Table 2 Additional parameters for pseudo-static and free-fi eld analysis(Wilson,1998; Rahmani and Pak,2012).

In the second step,after free-fi eld analysis,pile length above ground and superstructure were modeled.The pile was modeled as beam column elements with elastic section properties.The superstructure was modeled at the pile head.Generally,the superstructures above the pile foundations are multi-degree of freedom systems,but in the design of pile foundations,the superstructure was modeled as a single mass at the pile head to simplify the analysis.In this step,the base model was also fi xed.

The modelconsidered for the third step(pseudo-static analysis) is shown in Fig.1.There are two versions ofthe pseudo-static BNWF method.These two methods are different in the way in which the lateral load on pile due to ground movement(kinematic load)is considered.The fi rst BNWF requires free-fi eld soilmovements as an input.The free-fi eld soil displacements are imposed on the free ends of the p-y springs due to lateraldilatation layers.In the second BNWF,the limit pressures over the depth of the lateral spreading soilwere applied and the p-y springs were removed in this interval. In case of limit pressure,interaction of the soil and pile was not modeled,because the analysis is simple and can be done by hand calculation.Inertia forces from superstructure are represented as static forces applied simultaneously with lateral spreading demands.When limit pressures are applied directly to the pile nodes, bending moments and cap displacements depend on acceleration records and are greatly overpredicted for smallto mediummotions. This can be explained by the fact that the lateral spreading displacements were not large enough to mobilize limit pressures and actualpressures are smaller than limit pressures.However,for large motions,the pile cap displacements were considerably underpredicted(Brandenberg et al.,2007).In this paper,the free-fi eld soil movement was used as an input.The cap mass,multiplied by the maximum acceleration of the superstructure obtained from Step 2 as a lateral force(F),was applied at the pile head.The material properties of p-y curves for non-lique fi ed sand were computed based on API(1987).These curves are de fi ned by the following equation:

where Puis the ultimate bearing capacity at depth z,K is the initial modulus of subgrade reaction,and y is the lateral de fl ection.The initial tangent stiffness(Kin),based on Eq.(1),is obtained as Kin=Kz.The p-y curves were modeled as zero-length elements with PySimple1 materials.Under dynamic loading,the piles are in fl uenced by kinematic loads from lateral ground displacements and inertial loads from vibration of the superstructure.Fig.1 shows an idealized schematic of the BNWF model for kinematic(F)and inertial(Δs)loads.The loss of bearing capacity for piles in loose sandy soils(particularly vulnerable to liquefaction and lateral spreading during dynamic loading)also occurred.Therefore,the excessive forces imposed on the foundation due to ground displacement led to shearing ofthe piles and subsequent structural collapse of the superstructure.There are three methods for considering the in fl uence of liquefaction on p-y curves in sand.In the fi rst case,the lateralresistance oflique fi able sand is assumed to be zero.This method can lead to large design responses and high construction costs which may be very conservative(Rollins et al., 2005).Another approach is to treat lique fi able sand as undrained soft clay and use the p-y curves for soft clay.The undrained shear strength used in this case is obtained as a ratio of undrained shear strength to initialeffective overburden stress using fi eld data,and it is a function ofoverburden stress and relative density(Rollins et al., 2005;Varun,2010).The third method for the simulation of pile response in lique fi able soils is the use ofreduction factors,called pmultipliers.The p-y curves in lique fi able sand are multiplied by a factor usually between 0.01 and 0.3 to decrease the strength ofsand due to liquefaction(Rollins et al.,2005;Brandenberg et al.,2007; Varun,2010).In this paper,the third method(p-multipliers)was used.The free-fi eld soil displacement and lateralforce in head pile were imposed incrementally using a static load control integrator.

3.Validation of the proposed method

The performance and ability of the proposed approac h to simulate pile behavior in lique fi able soil have been demonstrated by comparison between the numerical simulations and centrifuge tests performed by Wilson(1998).In these tests,the soil pro fi le consisted of two horizontal layers of saturated uniformly graded Nevada sand(see Fig.2).On prototype scale,the lower layer was 11.4 m thick with relative density of80%(dense)and the upper was 9.1 mthick with relative density of35%(loose).The single pile was asteelpipe of 0.67 m in diameter,18.8 min length,and 19 mm in wall thickness.The pile tip was about 3.8 m above the container base. The superstructure mass(Ms)was 49.1 Mg.Properties of Nevada sand with Dr=35%and 80%are presented in Table 2.The Kobe acceleration record(Fig.3)was used as an input to shake model.

Fig.2.Layout of the model for centrifuge test by Wilson(1998).

It is important to specify stiffness and lateralresistance ofthe py curves in lique fi able soil as explained in Section 2.Three cases were considered to evaluate the effects ofvariations in stiffness and lateral resistance of the p-y curves on the testing results.These cases include:(1)use of the p-y curves without the in fl uence of liquefaction;(2)use of the p-y curves with a constant degradation factor in lique fi ed sand;and(3)use of the p-y curves with various degradation factors in lique fi able sand.In case(2),different degradation factors can be considered between 0.05 and 0.5 to reduce the strength of lique fi able soil.In this case,because of the smallstrength oflique fi able soil,especially that of surface ground,a degradation factor of 0.1 was considered.In case(3),variation in degradation factor with depth was taken from a smallvalue(top of lique fi able layer)to 1.0(bottom of lique fi able layer).An exponential decay function from bottom to top of lique fi ed layer is proposed as

where R is a degradation factor,as a function of distance from the top of the layer(z);H is the lique fi able layer thickness;and R0is the degradation factor at the top of the layer.Both the ultimate resistance and initial stiffness of the p-y curves in the lique fi able layer were taken to be R%of their unreduced magnitudes.

In free-fi eld analysis under the Kobe acceleration record scaled to 0.04g,0.12g and 0.22g,because of the ground level,lateral displacement(Δs)was less than about 5 cm and the effects of kinematic loads on seismic response are small.Therefore,in these tests,it is reasonable to only consider the inertial loads for calculation of the pile response.The superstructure displacement was calculated using acceleration of the superstructure obtained from the tests carried out by Wilson(1998).The comparison between the observed and simulated results of superstructure displacement is shown in Fig.4.In cases(2)and(3),by considering the centrifuge test results,the best predictions were obtained with degradation factor of 0.1.These results clearly illustrate that the performance and accuracy of BNWF mainly depend on the accuracy in selection of the correct curves.As seen in Fig.4,the de fl ections observed during the centrifuge test are much larger than those simulated without the in fl uence of liquefaction.This is due to the loss of bearing capacity for the piles in loose and medium sandy soils during dynamic loading.It can be noted that use of constant degradation factors at various depths gives unreasonable results. The pile head displacements have a good agreement with the available experimental data in case(3).

Fig.3.Acceleration record of Kobe earthquake scaled to 0.22g used in the centrifuge test by Wilson(1998).

Fig.4.Comparison of superstructure displacement in various cases with the centrifuge tests by Wilson(1998).

Fig.5 compares the maximum bending moment recorded from the centrifuge tests with that obtained frompresent analysis.In this fi gure,variation of R is similar to case(3)and Fig.5 shows that the results obtained from the numerical analysis agree with the values recorded during the centrifuge test.It can be said that increasing the value of R from a smallvalue at the top of the layer to 1.0 at the bottom of the layer produces a reasonable response for the piles. Therefore,this method was used for subsequent analysis.

4.Results and discussion

Fig.5.Comparison of bending moment pro fi les with the centrifuge tests by Wilson (1998).

In this section,the behavior of pile for various conditions is discussed.The soil pro fi le is the same as the one used in the centrifuge test performed by Wilson(1998).The pro fi le has two layers:the upper layer is lique fi able(relative density of 35%)whilethe lower layer(relative density of 80%)is not.Three different ground slopes of 1%,2%,and 4%were considered.The water table was supposed to be 1 m,2 m,3 m,and 4 m below the ground.This means that the thicknesses ofnon-lique fi able surface crust are 1 m, 2 m,3 m,and 4 m.The input motion for the model was a 20-cycles sinusoidalwave with a frequency of 2 Hz and the peak acceleration of 0.5g.It should be noted that the intensity,frequency content(e.g. predominant period)and the duration of strong shaking are important characteristics of an earthquake(Rathje et al.,1998). These characteristics affected the response of piles.The pile responses largely depend on the shaking amplitude.Increase in the shaking amplitude(because of more reduction of restraint on lique fi ed soil)resulted in a decrease in the restraint against bending under the lateral load,and the maximum bending moment in piles signi fi cantly increased(Gao et al.,2011).The frequency also had a signi fi cant effect on pile response.

The free-fi eld analysis showed that displacement of level ground is signi fi cantly less than that of the sloping ground.Fig.6 compares the displacement of sloping ground when the thickness of the non-lique fi able surface layer is 1 m and 2 m with ground slope of 2%.This fi gure highlights the importance of non-lique fi able surface layer as a key parameter on ground displacement.When liquefaction occurs in sloping ground,because of displacements developing up to several meters,large lateral forces may act on the pile.This phenomenon is commonly called lateral spreading(Klar et al.,2004).In lateral spreading,the driving forces only exceed the resisting forces during those portions of the earthquake that impose net inertialforces in the downslope direction.Each cycle of net inertial forces in the downslope direction causes the driving forces to exceed the resisting forces along the slip surface,resulting in progressively and incrementally lateral movement(Day,2002). Based on the results of free-fi eld analysis,the displacement pro fi le can be matched with constant displacement across the upper soil layer,a linear variation across the lique fi able and non-lique fi able layers.

Fig.6.Displacement pro fi le at two different thicknesses of non-lique fi able surface layer when the ground slope is 2%.

Fig.7.Variations in bending moment along the pile in different sloping grounds(free head,without superstructure).

The variations in bending moment along piles in different ground slopes for various conditions are presented in Figs.7-10. The results show that in sloping grounds,when a non-lique fi able soil layer overlies a lique fi able soil layer and piles are embedded in the non-lique fi able soil layer,the lateral spreading has more in fl uences on the damage of piles.An increase in bending moment occurred as the ground slope increased.After liquefaction,if the static shear stress caused by sloping ground is more than the shear strength of lique fi able soil,the non-lique fi able surface crust overlying a lique fi ed soil layer can slide with a considerable amount of displacement.In this condition(lateral spreading),the nonlique fi able surface layer was carried along with the underlying fully lique fi able soil and a large lateral force was imposed on the embedded piles(Ashour and Ardalan,2011).This force due to the lateral movement of the non-lique fi able layer has the potential to induce large bending moments in the piles leading to failure.

Fig.8.Variations in bending moment along the pile in different sloping grounds(fi xed head,without superstructure).

Fig.9.Variations in bending moment along the pile in different sloping grounds(free head,with superstructure).

The boundary condition of the pile head has an important effect on the pile responses(moments,shear and de fl ections).In layered soil deposits,a lique fi able soil layer is overlain by a non-lique fi able layer;when the pile head is free,the maximum bending moment develops at a depth corresponding to the interface of lique fi able and non-lique fi able layers(see Figs.7 and 9).When the pile head is fi xed,the maximum bending moment develops at two locations: (1)at the pile head and(2)at the interface of the two layers(see Figs.8 and 10).

Fig.10.Variations in bending moment along the pile in different sloping grounds (fi xed head,with superstructure).

The dynamic effects during earthquake on deep foundations are critically important.These effects include the kinematic forces applied by the soil to the pile foundation and the inertial forces of the superstructure due to earthquake.The combination of cyclic horizontal kinematic loads due to ground displacements and inertialloads from the superstructure determines the criticalload for piles during the shaking phase(Cubrinovski et al.,2009).The kinematic loads depend on the magnitude of ground deformations and the stiffness of the soil during a given loading cycle.Due to the in fl uence of liquefaction on free-fi eld soil response and soil-pilestructure interaction,the magnitudes of inertial and kinematic loads change(Han et al.,2007).When the acceleration of ground surface or superstructure mass is large or lateral dynamic stiffness of pile group due to pile and/or soil stiffness is small,the inertial effects may become important(Elahi et al.,2010).Figs.7 and 8 illustrate that in the absence of a superstructure,the maximum bending moment near the pile head decreases signi fi cantly,and a major difference is observed at that location between piles with and without superstructure,but the values are approximately unchanged at large depths(Figs.9 and 10).In other words,the same kinematic forces were developed in the piles with and without superstructure.At greater depths,where the inertial effects from the superstructure are less signi fi cant,pile damage can occur due to the lateral loads arising from lateral spreading(the excessive ground movement).Both inertial and kinematic loads can cause damages at the pile head.

The inertia effects of the superstructure before development of the pore water pressures and liquefaction are important and the kinematic effects can often be neglected.Ishihara(1997)stated that inertial forces are the cause of development of the maximum bending moment near the pile head.These forces are predominant before liquefaction and are con fi rmed by the results of Figs.7-10.If the shaking continues after liquefaction,the inertial forces are combined with kinematic forces on the pile foundation arising from large cyclic ground deformations.It can be said that the kinematic loading in the areas oflateralspreading with relatively strong nonlique fi able surface layers is important.Then,the pile failure near the bottom of the lique fi able layer is likely in fl uenced by kinematic loads from the lique fi able layer,while failure near the pile head is likely in fl uenced by inertial loads from the superstructure and kinematic loads from the non-lique fi able layer.It should be noted that the bending moments are underpredicted when the structural inertia forces are neglected.

The pile response is sensitive to the thickness of the nonlique fi able surface layer(H)and thickness of the lique fi able layer (L).Fig.11 shows variations in pile head displacement when the ratio of thickness(H/L)for different sloping grounds is increased. The pile head displacement increases to a peak value and then decreases with subsequent increase in thickness ratio.As the thickness of the non-lique fi able surface layer increases,horizontal kinematic loads due to ground displacements also increase andresult in higher pile head displacement.However,when the nonlique fi able surface layer is thick,because of increasing effective stress on the lique fi able layer,ground displacements are decreased, resulting in smaller values of pile head displacement.In addition, when the non-lique fi able surface layer is thick,due to increase of static shear stress in ground with great slopes,ground displacement and pile head displacement also increase.

Fig.11.Variations in pile head displacement against ratio of thickness(H/L).

5.Conclusions

This paper presents a method for analysis of piles in lique fi able soilunder seismic loads.Three steps for calculation ofpile response were:(1)free-fi eld response analysis using 3D numericalmodeling for calculation of ground surface acceleration and the maximum ground displacement along the length of the pile,(2)the dynamic analysis of pile length above ground and superstructure for calculation of the maximum acceleration of superstructure,and(3)1D Winkler analysis for calculation of pile response.All simulations in three steps were conducted using the open-source computational platform OpenSees.After veri fi cation ofthe numericalmodelusing a centrifuge test,analyses were carried out for various conditions.

By comparing the numerical results with the centrifuge test,it can be concluded that using the p-y curves with various degradation factors in lique fi able sand produces reasonable results.In addition,the non-lique fi able surface layer especially in sloping ground plays a key role in ground displacement.When the pile head is free,the maximum bending moment develops at a depth corresponding to the interface of lique fi able and non-lique fi able layers.When the pile head is fi xed,there are two locations for developing the maximum bending moment:(1)at the pile head and(2)at the interface of the two layers.Moreover,at greater depths,where inertial effects from the superstructure are less signi fi cant,pile damage may occur due to lateralloads arising from lateral spreading.Both inertial and kinematic loads can cause damages at the pile head.

Con fl ict of interest

The author con fi rms that there are no known con fl icts of interest associated with this publication and there has been no signi fi cant fi nancial support for this work that could have in fl uenced its outcome.

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Ali Zahmatkeshwas born in 1984 in Ferdows,Khorasan, Iran.He received his M.Sc.degree in Geotechnical Engineering from Mazandaran University,Iran in 2010.Since 2012,he is a Ph.D.student at Babol University of Technology.His thesis topic is Analysis of Performance of Pile Foundations in Lique fi ed Soils.His research interests cover soil improvement,soil liquefaction and numerical modeling.

*Corresponding author.Tel.:+98 9158342367.

E-mail address:A.zahmatkesh@stu.nit.ac.ir(A.Zahmatkesh).

Peer review under responsibility of Institute of Rock and Soil Mechanics,Chinese Academy of Sciences.

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http://dx.doi.org/10.1016/j.jrmge.2015.05.001