Influence of a weak layer on the tunnel face stability – Reliability and sensitivity analysis

Abstract

In this study, reliability and sensitivity analyses were employed to investigate the effects of a weak interlayer on tunnel face stability. Due to the irregular geology process and the movement of tunnelling machine, the situations of weak soils encountered during tunnel construction are complex and variable. To address this problem, this paper adopted reliability and sensitivity analysis to evaluate the face stability of a tunnel considering a weak soil layer. An active learning method which combines Kriging and Monte Carlo Simulation (AK-MCS) was used for the reliability analysis. Then, the importance of each stochastic soil property was estimated by coupling the surrogate model constructed in the AK-MCS with the global sensitivity analysis (GSA). Compared with traditional approaches, the employed technique (termed as AK-MCS-GSA) is able to provide a variety of interesting results (failure probability, model response statistics and sensitivity index) but with a greatly reduced computational time. The obtained results permitted to show that a weak soil layer over the tunnel cross-section can lead to a significant increase of failure probability. Additionally, the sensitivity indices in GSA revealed that the soil's frictional angle of the weak layer has the greatest influence on the face stability. Moreover, the impacts of varying the weak layer’s position and thickness are discussed. The critical position for the weak layer which leads to the biggest failure probability is remarked.