Reliability assessment of excavation-related movements of underground structures

A major consideration in the design of excavation-related underground structures is the prediction of the movements associated with the construction operations. Excessive movements can lead to failure of the geotechnical structure or adjacent facilities. Most analytical methods currently used to estimate these deformations are deterministic, and ignore the many associated uncertainties such as the variability of the loadings and the variability of the geotechnical properties. A risk-based approach to performance failure is necessary to incorporate systematically the uncertainties associated with the various design parameters. This paper summarizes the procedure to assess the reliability of displacements associated with excavation-related construction activities such as tunnels and braced excavation systems using the first-order reliability method. Examples are presented to illustrate feasibility of the proposed method. With this method, it is possible to carry out sensitivity studies to examine the effect of the level of uncertainty of each parameter on the probability that the displacement-related limit state has been exceeded.