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Numerical Analysis of Pile–Soil Interaction under Axial and Lateral Loads
Yasser Khodair
Ahmed Abdel-Mohti
p Khy
In this paper, the analysis of a numerical study of pile-soil interaction subjected to axial and lateral loads is presented. An analysis of the composite pile-soil system was performed using the finite difference (FD) software LPILE. Two three dimensional, finite element (FE) models of pile-soil interaction have been developed using Abaqus/Cae and SAP2000 to study the effect of lateral loading on pile embedded in clay. A lateral displacement of 2 cm was applied to the top of the pile, which is embedded into the concrete pile cap, while maintaining a zero slope in a guided fixation. A comparison between the bending moments and lateral displacements along the depth of the pile obtained from the FD solutions and FE was performed. A parametric study was conducted to study the effect of crucial design parameters such as the soil's modulus of elasticity, radius of the soil surrounding the pile in Abaqus/Cae, and the number of springs in SAP2000. A close correlation is found between the results obtained by the FE models and the FD solution. The results indicated that increasing the amount of clay surrounding the piles reduces the induced bending moments and lateral displacements in the piles and hence increases its capacity to resist lateral loading.
1. Introduction
The soil-structure interaction in general has been a
concern; therefore, more research is needed to further
understand and better model this interaction (Abdel-Mohti and
Pekcan 2013a, b), Khodair and Hassiotis (2013). The
primary purpose of using piles is to transfer the loads from the
superstructure and the abutment to a reliable soil, in cases
where the soil near the ground surface can not support the
applied loads. Piles can transfer both axial and lateral forces.
As the pile is subjected to lateral loads, the soil mass
surrounding the pile plays a key-role in providing lateral
support for the pile. The nature of pilesoil interaction is three
dimensional and to complicate the problem further, soil is a
nonlinear and anisotropic medium. Therefore, finding a
closed form solution to such problem is extremely difficult.
Several methods have been used to predict the response of
the composite pilesoil system. The persistent obstacle in
such processes is to find a valid approximation for soil
representation. The subgrade reaction approach provides the
simplest solution for the pilesoil interaction problem. In this
where x is length along pile, and EpIp is the flexural stiffness
of pile. The solution for the differential equation are readily
available and can be found in Hetenyi (1946). The subgrade
reaction has been widely accepted in the analysis of
soilstructure interaction problems (Reese and Matlock 1956;
Broms 1964). However, a drawback of the method is its
inability to account for the continuity of soil. Additionally,
the linear representation of the subgrade reaction for the soil
elements along the depth of the pile fails to account for the
non-linear nature of the soil. The p-y approach is another
method for handling pilesoil interaction. The only
difference between the p-y method and the subgrade reaction
method is that the former is based on defining a nonlinear
relationship between the soil reaction and the lateral
deflection at each point along the depth of the pile.
Therefore, a p-y relationship is defined at each distinctive point
along the depth of the pile. The solution to Eq. (2) can be
obtained using the finite difference method and computers.
Appropriate boundary conditions must be imposed at the
pile head to insure that the equations of equilibrium and
compatibility are satisfied at the interface between the pile
and the superstructure. The concept of a p-y curve was first
introduced by McCelland and Focht (1958). The
development of a set of p-y curves can introduce a solution to the
differential equation in Eq. (2), and provide a solution for the
pile deflection, pile rotation, bending moment, shear, and
soil reaction for any load capable of being sustained by the
pile. Several methods to obtain p-y curves have been
presented in the literature (Georgiadis and Butterfield 1982;
ONeill and Gazioglu 1984; Dunnavant and ONeill 1989).
These methods rely on the results of several empirical
measurements. Some researchers such as Ruesta and
Townsend (1997) and Gabr et al. (1994) have attempted to
enhance p-y curve evaluation based on in situ tests such as
cone penetration, pressuremeter and dilatometer. However,
such attempts have focused on the soil part of soil pile
interaction behaviors. Robertson et al. (1985) developed a
method that used the results of a pushed in pressuremeter to
evaluate p-y curves of a driven displacement pile. Attempts
towards deriving p-y curves using three dimensional finite
element model has been provided by Brown Dan and Shie
(1990, 1991). A simple elasticplastic material model is used
for the soil to model undrained static loading in clay soils.
p-y curves are developed (...truncated)