A Study on Analytic Models of Retaining Walls for Un-Symmetrical ...

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A Study on Analytic Models of Retaining Walls for Un-Symmetrical Excavations

Yen Twu Kuo
Department of Civil Engineering, National Cheng Kung University Department,
Tainan City, TAIWAN, China








ABSTRACT


With considering large geometric deformation principle and materials’
non-linear behavior, the interactive behaviors between soil and
structure for un-symmetrical excavations were investigated by using 2-
D plane strain model based upon theory of continua mechanics and
finite difference method in this paper. An un-symmetrical cross section
of deep excavation with four different types of soil will be discussed.
According to the comparison between classic analytic model and
continua mechanics model; (1) on the design of the retaining wall and
related strut system at un-symmetrical position, the active lateral earth
pressure was found much larger than Rankine’s predication. (2) The
analytic displacements and bending moment calculated by continua
mechanics theory have bean proved to be consisted with the
experimental results measured in the job site for each excavation step.


KEY WORDS:
earth pressure, soil-structure interaction.

INTRODUCTION


Considering design of retaining wall, Rankine’s and Columb’s earth
pressure theories are commonly adopted for the assumption of lateral
earth pressure against upon retaining wall. The deformation of braced
wall differs from that of retaining wall, because the rotation is not
simply about top or bottom of the wall. For this reason, neither
Rankine’s nor Columb’s theory may predict the actual earth pressure
distribution. (Terzaghi and Peck, 1967; Kim and Preber, 1969; Sherif et
al, 1984; Das, 1975, 1994)

For the limit purpose of the particular use on the base, un-symmetrical
excavations were to be adopted. Therefore, some worthy researches
were established:

1. If the cutting lateral section is symmetrical, we can assume that
the horizontal displacement on the symmetrical line is zero and
analyze the slurry walls by using the classic ultimate earth
pressure theory. However, it should be considered whether the
domain is far enough to cover the failure wedge. When the un-
symmetrical cutting is proceeding, the classic ultimate earth
pressure theory based on the assumption for semi-infinite
domain is no longer applicable. Because of the limit of cutting
width, the failure wedge might not be formed. Therefore, what
kind of analytic models should we properly select on the design
of the underground retaining walls and related strut system for
un-symmetrical excavations?
2. Checking the sliding tendency under the unbalanced earth block
was based on the classic lateral earth pressure theory. For the
earth block between two adjacent walls, the stresses acting along
two sides are unequal (block A and block B, shown as the
hatched areas in Fig.1). Therefore, a shear stress will be
engendered under the earth block in order to keep equilibrium.
Traditionally, the average shear stress distribution was used to
check the safety of sliding and overturning of retaining wall.
Meanwhile, no other theory and measured data to prove how the
earth pressure distributes on un-symmetrical excavations. Thus,
the applicability of the analytic model mentioned above needs to
be discussed.
3. What will the active and passive earth pressures of the two
exterior slurry walls perform during the process of un-
symmetrical cutting? (Tsui, 1974; Cundall, 1976; Desai, 1977;
Mana, 1978, 1981; Pott, 1986;Oh, 1988; Bowles, 1988; Tusi,
1989; Wong, 1989; Simpson, 1992)
4. An experimental project was executed in the job site, which is
located in Tainan City Taiwan. This is a underground parking lot
beneath the Hai-An Street. The underground RC structure is 816
metes long, 40 meters width, 3 metes embedded depth, the first
and second basement flours were. Planed for parking area, the
third basement floor was used for mechanical and electrical
equipment space. The main purpose of the testing was aimed at
collecting the measured data in order to investigate the lateral
displacements and the bending moments of the slurry wall, as
well as the axial forces in the braced struts according to
excavated stage. The main factors considered in the back
analysis study of the soil-structure interactive system were
stiffness of the slurry wall and the struts, joint stiffness of the
strut, stress-strain relationships for the soil, quantity of the
preloading. The comparison between the theoretical calculations
and testing results could be used to proved the modern computer
program based on the theory of continua mechanics to be
adapted for the study in geotechnical engineering.
Proceedings of The Thirteenth (2003) International Offshore and Polar Engineering Conference
Honolulu,Hawaii,USA,May 25

30,2003
Copyright © 2003 by The International Society of Offshore and Polar Engineers
ISBN 1

880653
-
60

5 (Set);ISSN 1098

6189 (Set)
683