Increasing the passive resistance of deep excavations in very soft soils to mitigate ground movements through centrifuge modelling

Abstract

The increasing scale of construction projects in cities puts greater pressure on limited land resource. This leads to developers maximising returns by constructing taller structures and deeper basements. Surface settlements associated with deep excavations in soft soils are considerably greater in magnitude and extent compared with movements that develop in stiff soils. For this reason, in areas with thick deposits of soft soils, such as Mexico, St Petersburg and major urban areas in the far East, controlling ground movements arising from deep excavations is critical.This paper describes a series of centrifuge model tests, conducted at 160g, to determine the influence of various construction techniques on surface and subsurface displacements arising when a very stiff embedded retaining wall was used to support a deep excavation in very soft soils. The wall stiffness was designed such that it effectively eliminated lateral wall deflections thereby allowing movements resulting from basal heave to be isolated. This permitted the influence of a distinct construction methods aimed at controlling basal heave to be explored. This comprised the construction of an additional lower stiffness wall ahead of the primary retaining wall to increase the passive resistance of the excavation.