Probabilistic Assessment of Serviceability Limit State of Diaphragm Walls for Braced Excavation in Clays

Abstract

Braced excavation systems are commonly required to ensure stability in the construction of basements for shopping malls and underground transportation facilities. For excavations in deposits of soft clays, stiff retaining wall systems such as diaphragm walls help to restrain ground movements and wall deflections in order to prevent damage to nearby buildings and utilities. It is quite common for designers to limit the maximum wall deflection to 0.5% times the maximum excavation depth. However, a review of measured diaphragm wall displacements from various published case histories of successful deep excavations show that wall deflections can be up to more than 2% times the excavation depth. Since the allowable threshold wall displacement depends on various influencing parameters, wall deflections should not be limited to an arbitrary value. This paper presents a probabilistic framework combining a simplified wall deflection estimation model with reliability methods to determine the probability of serviceability limit state failure. Consequently, using this approach, the paper presents a methodology that allows engineers to determine the required threshold limiting