Mechanism of buttress walls in restraining the wall deflection caused by deep excavation

Abstract

This objective of this study is to investigate the mechanism and characteristics of buttress walls in restraining the wall deflection in deep excavations. The three-dimensional finite element method was used to carry out a series of parametric studies on the length, spacing, thickness, depth, and demolished sequence of buttress walls. The results indicated the following: when buttress walls were demolished along with excavation, the flexural rigidity enhanced by buttress walls to the diaphragm wall was unable to effectively reduce the deflection of a diaphragm wall; the effect of a buttress wall restraining the wall deflection mainly came from the frictional resistance between the surface of the buttress wall and the surrounding soils, thus, a longer length of buttress wall provided a greater effect. When the buttress wall was maintained during excavation, the buttress wall could effectively restrain the wall deflection; in addition to the frictional resistance between the surface and surrounding soils, the flexural rigidity of buttress walls could provide restraining effects on the deformation of the diaphragm wall. The influence of the thickness of a buttress wall on the wall deflection was insignificant for the maintained buttress wall. Under the conditions of equivalent total length of buttress wall, the restraining effect of increasing the length of a buttress wall was greater than that resulting from reducing the spacing between buttress walls. To effectively utilize the flexural rigidity enhanced by buttress walls to the diaphragm wall, buttress walls above the final excavation should be maintained until the end of excavation.