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Effect of Excavation-induced Movements on Adjacent Piles
Effets des mouvements causés par une excavation sur les pieux voisins
Elkady T.
Faculty of Engineering, Cairo University, Giza, Egypt (Currently, King Saud University, Riyadh, Saudi Arabia)
ABSTRACT: This paper aims at investigating the effect of excavation-induced movements on the lateral deflections and bending
moments of piles situated within the influence zone of a cantilever side-supported excavation. For this purpose, a series of non-linear
finite element analyses were performed to assess the effects of excavation depth, distance of the pile from the side supported
excavation, pile stiffness, and wall stiffness. Results indicate that distance of pile from side supported excavation and excavation
depth have a significant effect on the lateral deformations and bending moment of the pile; while side support stiffness has a less
markable effect. Charts for the preliminary evaluation of pile head lateral deflection and bending moments in piles were developed.
RÉSUMÉ : Cet article vise à examiner l'effet des mouvements induits par une excavation sur les déformations latérales et les
moments de flexion des pieux placés dans la zone d'influence d’une excavation soutenu par un mur encastré. Dans ce but, une série
d'analyses aux éléments finis non-linéaires a été réalisée pour évaluer les effets de la profondeur de l’excavation, de la distance du
pieu à la paroi de l’excavation, du diamètre du pieu et de la rigidité du mur. Les résultats montrent que la distance de pieu à la paroi et
la profondeur de l’excavation ont un effet significatif sur les déformations latérales et le moment de flexion du pieu; alors que la
rigidité du mur a moins d'effet. Des diagrammes pour l'évaluation préliminaire du déplacement latéral de la tête du pieu et des
moments de flexion dans le pieu ont été établis.
KEYWORDS: Finite element, pile, side-supported excavation.
1 INTRODUCTION.
Side-supported deep excavations are typically performed in
urban densely populated cities for the construction of basements
and cut and cover tunnels. Inspite of quality control applied
during side support constrcution, some degree of side support
lateral movement is unavoidable. This lateral movement is
expected to generate lateral movements in soil, which in turn
affect the perfomance of nearby pile foundations. Soil lateral
movements will impose addtional lateral deflection and bending
moment to the pile.
Several researches have used numerical modeling to evaluate
the performance of pile adjacent to side supported excavations.
Finno et al. (1991) and Goh et al. (2003) used lateral
movements observed in the field to examine the behavior of a
nearby pile. Finno et al. (1991) adopted a plane strain finite
element code; while Goh et al. (2003) used a simple analytical
model where the pile was discretized into discrete (linear
elestic) beam elements with the soil-pile interaction modeled
using a series of non-linear springs. Ong et al. (2006) and
Leung et al (2006) used a numerical analysis similar to that
adopted by Goh et al (2003) and obtained good agreement with
results of centrifuge models of a single pile in clay and dense
sand nearby a side-supported excavation. Although research
exists for the use of three-dimensional finite element in
analyzing the response of piles due to lateral soil movements
and open excavations; there is limited research directed towards
analyzing performance of pile under coupled wall-soil-pile
interaction (Pan et al 2002, Miao et. al 2006, Kok et al. 2009).
This paper presents the results of numerical simulations
performed using a 3D finite element approach to evaluate the
behavior of a single pile nearby a cantilever side-supported
excavation. Design variables considered in this study included
pile stiffness, wall stiffness, distance of pile from side-support,
and excavation depth. Relative contribution of the different
design variables on the pile head lateral deflection and
maximum bending moment was discussed.
1 FINITE ELEMENT ANALYSIS
1.1
Finite element mesh
Three-dimensional stress deformation analyses were performed
using the finite element program ABAQUS (2010). The model
consists of three parts; namely, soil, pile and wall of depth 10
m. Soil and piles in the model were discretized using solid
tetrahdron elements that have nodes with 6 degrees of freedom.
The wall was modelded as a planar shell that have both axial
and bending stiffness. Main features and dimensions of the
finite element model is shown in Figure 1.
Figure 1. Finite Element Mesh
Interaction at the pile-soil and wall-soil interface was
modeled using a master-slave surface contact formulation
developed by Hibbitt et al. (1998) and built in ABAQUS. In
