2835
Analysis of Piles Supporting Excavation Adjacent to Existing Buildings
Analyse de pieux de bâtiments existant en cours de fouilles sous-jacentes
Ramadan E.H., Ramadan M., Khashila M.M.
Civil Eng. Dept., Faculty of Engineering, Assiut University, Egypt
Kenawi M.A.
Civil Eng. Dept., Faculty of Engineering, Sohag University, Egypt
ABSTRACT: In urban environment, excavation adjacent to existing buildings is common. Supporting excavation is important to
prevent damaging of the adjacent buildings. There are many factors affecting the selection of the supporting system. Some of them are
soil behavior, type of foundation, foundation level of the adjacent buildings, and the budget of the project under construction. In order
to reduce the surrounding soil movement due to deep excavation, a three dimensional Finite Element (3D FE) study was carried out in
this paper, considering soil-structure interaction. A piled supporting system was selected because it is common and relatively
economic to use in cohesive soil in Egypt. A parametric study was performed to study the effect of the stiffness of the supporting
system on minimizing the ground deformation. From the results, some recommendations are given in terms of excavation depth, soil-
pile stiffness, and pile embedded depth.
RÉSUMÉ : En milieu urbain, les excavations sous-jacentes aux bâtiments existants sont courantes. Soutenir les fouilles pour prévenir
des endommagements sur les bâtiments est donc très important. Il y a plusieurs facteurs qui influencent les choix des systèmes de
renforcement. Par exemple, le comportement du sol, le type de fondation, la profondeur des fondations et enfin le coût des travaux.
Afin de limiter les désordres occasionnés par une excavation profonde, une étude numérique tridimensionnelle (méthode aux éléments
fins) a été réalisée dans cet article en prenant en compte l’interaction sol-structure. Un ensemble de pieux supports a été considéré car
il est relativement économique et très commun dans les sols Egyptiens. Une étude paramétrique a été réalisée pour étudier la rigidité
du système qui minimise les déformations du sol. A partir des résultats, des recommandations sont données en termes de profondeur
d'excavation, de rigidité sol-pieu, et de profondeur de fondation.
KEYWORDS: excavation, pile wall, clay, adjacent building.
1 INTRODUCTION
In urban environment in Egypt most buildings in the same block
area are adjacent to each other. No distance between buildings
exists due to high population intensity along the river Nile
Valley. These conditions increased the tendency to build high
rise buildings. Most of these new high rise buildings are built
adjacent to old existing buildings. The adjacent old buildings
condition is usually critical either due to the weakness of the
structure system of the building or the foundation level is at
shallow depth. High rise buildings with basements need deeper
excavation than the foundation level of the adjacent building.
With the presence of adjacent shallow foundation, the
excavation will cause large soil movement and damage to the
adjacent building, as shown in Fig. (1). Many failure cases were
observed due to unsupported excavations. It is common, in
Egypt, to use contiguous pile wall to support the excavation on
the adjacent buildings sides. Such type of wall is economic and
effective in cohesive soil. The excavation will cause lateral and
vertical soil movement, the first component is considered to be
more critical for adjacent piles. The design of these excavations
should include an estimation of the ground movement as well as
stability check of the adjacent buildings. The lateral loads
resulting from the soil movements induce bending moments and
deflections in the piles supporting excavation, which may lead
to structural distress or failure of both the existing building and
the excavation supporting system. Indeed, several instances of
structural damage to piles have been reported in the literature,
for example, Hagertry and Peck 1971 and Finno et al. 1991, as
reported by Chen and Poulos 1997.
Many theoretical and empirical methods have been
established for solving certain types of excavation problems, for
example, Poulos and Chen 1995, Hashash and Whittle 1996, Ou
et. al 1996, Poulos and Chen 1996, Chen and Poulos 1997,
Poulos and Chen 1997 and Leung et. al 2000. They studied the
failure of the excavation with no adjacent buildings or
additional loads close to the excavation. In other cases, they
studied the effect of soil movement during the excavation on the
behavior of adjacent existing piles. However, the design of
supporting system for excavation adjacent to existing building
founded on shallow foundation is not studied enough. Many
parameters could affect the design of pile supporting
excavation. This includes excavation height, soil properties, the
foundation type and the foundation level of the adjacent
building.
The present study mainly aims to provide recommendations
for the design of contiguous pile wall in cohesive soil. Three
Dimensional Finite Element Modeling (3D FEM) was used to
carry out the study. PLAXIS 3D Foundation software was used
in the analysis. Different parameters were considered in the
study. The ranges of the selected parameters were limited to the
common cases in Egypt and as recommended by the Egyptian
Code of Practice (ECP).
2 FINITE ELEMENT MODEL (FEM)
2.1
Geometry and meshing
FEM meshing and geometry is shown in Fig. (2). The figure
shows a cut at the face of the excavation. Soil above the
foundation level was removed only to show footing shape in the
figure. However, it was included in the analysis. Model
dimensions were selected so that the boundaries are far enough
to cause any restriction or strain localization to the analysis. The
excavation area is 10 x 10 m. For simplicity, the foundation of
the adjacent building was assumed to be three strip footings of
10 m length and 2 m width each and in between distance of 2 m.
