Deterministic and Probabilistic Investigations of Piping Occurrence during Tunneling through Spatially Variable Soils

Abstract

Piping is a common phenomenon of seepage failure in underground space construction. Efforts have been made in understanding the mechanism of piping due to seepage gradient force and incorporating these in prediction technologies. In this study, the characteristics of seepage and piping occurrence during the excavation of a riverside tunnel are discussed based on hydraulic-mechanical coupling analysis. Four typical cut-off wall depths are considered to evaluate the effectiveness of different seepage-control measures, and two different water depths are used to assess the impact of water depth. The spatial variability of hydraulic conductivity, which is often the case in reality, is incorporated into the program of the finite-element method. Results reveal that hydraulic conductivity is a key factor affecting the formation of potentially dangerous seepage path and the probability of piping occurrence. When the spatial randomness in hydraulic conductivity is considered, the riverside tunnel is observed as being much more susceptible to piping. By contrast, the assumption of uniformity in hydraulic conductivity may yield an inaccurate estimation of the risk in tunneling. The results make it possible to visualize the potential seepage path and provide a better explanation of the piping mechanism.