Reliability Assessment of Basal-Heave Stability for Braced Excavations in Clay

One potential failure mechanism that needs to be considered for the design of braced excavations in soft clays is basal-heave instability. Many uncertainties are associated with the calculation of the basal-heave factor of safety, including the variabilities of the loadings, geotechnical soil properties, and engineering and geometrical properties of the wall. A risk-based approach to failure is necessary to incorporate systematically the uncertainties associated with the various design parameters. This paper demonstrates the potential for the reliability index–based approach for evaluating the basal-heave stability of braced excavations in clay. By using basic structural reliability concepts that reflect the degree of uncertainty of the underlying random variables in the analyses, engineers will have increased awareness of the uncertainties and their effects on the probability of failure. This study shows that the assumption of a linear limit state (failure) surface can be used to provide reasonable estimates of the reliability index and the probability of failure. Mathematical expressions, tables, and charts have been provided to estimate the probability of basal-heave failure for wide and deep excavations.