Seismic Analysis of Soil-pile Interaction under Various ... · assessing from the seismic...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 18 (2017) pp. 7566-7571

© Research India Publications. http://www.ripublication.com

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Seismic Analysis of Soil-pile Interaction under Various Soil Conditions

Preeti Codoori

Assistant Professor, Department of Civil Engineering, Gokaraju Rangaraju Institute of Engineering and Technology, Telangana State, India.

Orcid Id: 0000-0002-8505-3448

Jagan Mohan Kummari

Ph.D Scholar, School of Engineering, RMIT University, Victoria, Australia.

Orcid Id: 0000-0002-9616-9075

Abstract

Study of Soil-Pile interaction is an important consideration in

evaluating the seismic performance of pile-group supported

structures, particularly in soft clay or liquefiable soils.

Additionally, dynamic deformations can also get induced

within the structure due to the underneath soft soils. An

understanding from historical catastrophic earthquakes

evidently demonstrated that the ground motions were

responsible for the failure of foundations, which in turn have

caused damage to the structures, leading to the majority of

property loss and casualties. In view of the necessity to

precisely predict the response of a pile in a soil-structure

interaction problem during an earthquake, in this paper,

numerical analysis of a single pile subjected to the 1940 El

Centro earthquake (Mw 6.9) ground motion was carried out to

understand the soil-pile interaction for different soil

conditions, namely, C-soil, Ø-soil, and C-Ø soil. The axi-

symmetric numerical model was developed by using Finite

Element Program “OpenSeesPL”, to understand the soil pile

interaction for the dynamic earthquake loading condition.

Response profiles, displacements response time history at the

base and at the crest, and stress contours are studied to

understand the behavior of short and long piles in various soil

conditions.

Keywords: Soil-pile interaction, rigid and flexible piles,

Open-sees PL, C, Ø, and C-Ø soils.

INTRODUCTION

Piles are generally used in soft, liquefiable soils and often in

very soft rocks which have spread to the substantial depth.

The geological map of India (Fig.1.) shows the formation of

recent sedimentary and Pleistocene alluvial soils spread over

the plains of north India. These soils since formed from the

river deposits are new and are susceptible for liquefaction

during earthquakes. Shallow foundations in such soils are not

cost-effective and they in turn perform poor for the dynamic

load cases and fail under bearing capacity of the boundary

domain i.e. soil. Coincidentally, these north Indian plains

experience earthquakes of moderate to high intensity (Fig.2.).

Additionally, these soils because of their rich mineral sources

are inhabited more. Fig.3. shows the density of housing in

these districts. Combined with the seismicity in the area and

construction practices, the housing risk factor faced by the

residents in these areas is high and is presented in Fig.4.

Structures supported by piles or pile-groups can be an

imperative solution, predominantly for soft clay and

liquefiable soils. The phenomenon could be understood by

assessing from the seismic performance analysis of pile, pile-

group and pile-group supported with structures. However, it is

essential to precisely predict the structures response

considering the soil-structure interaction. Soil-pile interaction

during an earthquake is a complex study and thus is not

always taken into analysis for the seismic design of structures.

Based on the information from Fig.1 to 4 and Table 1, it is

understood that the north Indian plains need piles to support

the structures safe from earthquakes and earthquake triggered

liquefaction.

In this paper, the response of a short and long pile for the

1940 El Centro earthquake (Mw 6.9) ground motion has been

presented. For the analysis, OpenSeesPL finite element

software has been employed. A short and a long pile are

modeled in three soil types, namely, C-soil, Ø-soil, and C-Ø

soil, for which the time-history analysis has been performed.

In the numerical analysis, the soil-pile interaction is achieved

by representing boundary conditions of a pile with discrete

non-linear springs with the stiffness equal to the equivalent

soil subgrade reaction.



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Figure 1: Geological Map of India showing recent

Sedimentary and Pleistocene Alluvial soils spread over the

plains of north India (Source: mapsofindia.com)

Table 1: Intensity corresponding to different zones as per IS

1893 (Part-I): 2007 and number of houses in each zone

(Pradeep, 2016)

Zon

e

Seismic

Zone

Factor (Z)

Seismic

Intensity

Houses

Number

Percen

tage

(%)

II 0.10 VI (or

lower)

4,39,86,517 17.78

III 0.16 VII 11,

58,68,042

46.86

IV 0.24 VIII 6,32,82,128 25.00

V 0.36 IX (or

higher)

2,41,44,350 9.76

Figure 2: Seismic Zonation Map of India (IS 1893: 2002)

Figure 3: Housing density in the districts of India (Census of

India, 2011 and Pradeep, 2014)

Figure 4: Housing risk factor in the districts of India

(Pradeep, 2016)

Numerical Modeling of Soil-Pile interaction

The numerical analysis is performed by using OpenSeesPL.

Developed by the Regents of the University of California

(2000), is a graphical user interface (GUI) for three-

dimensional (3D) soil-pile interaction responses. The base

shaking simulation is performed with a control boundary

conditions and zero inclination mode. The pile is modelled

with linear beam element and soil with nonlinear beam

element. The interface between pile and soil is simulated with

zero-length elements. These elements connect the fixed node

of pile with slave spring nodes of soil.

Soil Properties

The different types of soils considered for the analysis are

homogeneous, namely, purely cohesive (C-soil), purely non-

cohesive (Ø-soil) and combination of both (C-Ø soil). Table 2,



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explains the different soil parameters of the soils considered

for the analysis.

Table 2: Soil types and their parameters

Soil Parameters C-Soil Ø-Soil C-Ø Soil

Shear Modulus, G (kPa) 6x104 13x104 10x104

Bulk Modulus, K (kN/m2) 3x105 39x104 2.3x104

Cohesion, C (kN/m2) 37 0.3 25

Coeff. of Permeability, (m/s) 1x10-9 1x10-7 1x10-4

Mass density (Mg/m3) 1.5 2.1 1.9

Friction Angle (Degrees) 0o 40o 33.5o

Pile Properties

Numerical analysis is carried out for circular rigid short and

flexible long concrete piles. The lengths of 4.5 m and 18 m

respectively are modeled with a diameter 0.5 m. The pile is

fixed at the bottom and pinned at the top to find its response

against the given dynamic load. The short and long piles are

modeled with a semi-infinite soil medium of size 25m x 25m

x 9m, and 40m x 40m x 36m, to simulate the soil structure

interaction phenomenon. Fig.5. shows half-mesh Soil-Pile

interactive model considered for the dynamic analysis.

a)

(b)

Figure 5: Soil-Pile finite element models generated for (a)

Short Pile (b) Long Pile

Dynamic analysis of the soil pile interaction model

A dynamic load in the form of El Centro ground motion (Mw

6.9) with peak ground acceleration of 0.348g is applied at the

base of the soil model, to perform the analysis. The

acceleration time history of the ground motion used for the

study is shown in Fig.6. Fig.7. shows the Fourier Amplitude

Spectra of El Centro ground motion. Fig.8. shows the IS 1893

design response spectra and El Centro ground motion

response spectra.

Figure 6: Acceleration time history of 1940 El Centro

earthquake ground motion (Mw 6.9)

Figure 7: Fourier Amplitude Spectra of El Centro ground

motion

Figure 8: IS 1893 (Part 1): 2002 design response spectra and

El Centro ground motion response spectra

RESULTS

For the given ground motion, response profiles for short and

long piles are observed in the direction of the lateral load

applied and are shown in Fig.9&10. The displacement

response time histories at the base and top of the short and



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long piles for different soil types are presented in Fig.11&12.

Amplification of displacement response is observed at the top

of the pile. Fig.13&14 shows the stress contours for short and

long piles modeled in different soil strata. It is observed that

the displacements and stresses high for C-Ø soil.

Figure 9: Short pile response profile for different soil types

Figure 10: Long pile response profile for different soil types

Figure 11: Displacement response time history of short pile at

the base and at the crest for a) Ø-Cohesionless soil b) C-

Cohesive soil c) C-Ø soil

Figure 12: Displacement response time history of long pile at

the base and at the crest for a) Ø-Cohesionless soil b) C-

Cohesive soil c) C-Ø soil

a)

b)

c)

Figure 13: Longitudinal stress [kPa] profiles observed in the

soil and short pile subjected to El Centro earthquake ground

motion for a) Ø-Cohesionless soil b) C-Cohesive soil c) C-Ø

soil



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a)

b)

c)

Figure 14: Longitudinal stress [kPa] profiles observed in the

soil and long pile subjected to El Centro earthquake ground

motion for a) Ø-Cohesionless soil b) C-Cohesive soil c) C-Ø

soil

SUMMARY AND CONCLUSIONS

To carry comparative study on soil pile interaction for long

and short pile for different soil types like C-soil, Ø-soil and C-

Ø soil, time history analysis has been carried out on the finite

element models.

Subsequent are some interpretations drawn from the existent

study

1. For short rigid short pile and flexible long pile, the

peak displacements at the top of the pile are found to be

less for C-Ø soil as compared to C-soil and Ø-soil.

2. The values of peak displacements are more for long

pile than the short pile; hence length of the pile is one

of the important parameter for displacement controls.

3. The grade of the concrete is not influencing the

displacement characteristics of the pile. Change in

displacements is negligible for the parametric grades

considered for the present study.

4. The type of surrounding soil of the pile plays an

important role in the displacements at the top of the

pile.

The finite element tool is found to be easy to understand and

operate for the interaction problem.

NOTATIONS

Ø-Cohesionless soil

C-Cohesive soil

C-Ø combination soil having both the cohesive and

cohesionless material

γ and β Newmark’s integration coefficients

REFERENCES

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analysis of piles in liquefiable soils: Parametric

evaluation of liquefied layer properties”. Bulletin of the

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41, pp.234-246, 2008.

[2] Budhu M. and Davies T. G, “Nonlinear analysis of

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(5ICEE)- 2010. Tokyo Institute of Technology, Tokyo,

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