The inherent spatial variability of soil properties has been considered as one of the main sources of uncertainties in geotechnical problems. The need for probabilistic analysis of the tunnel face stability that takes into account the variability of soil properties has been acknowledged. This article employed a probabilistic-based method, called random finite difference method, for evaluating the stability of tunnel face under the influence of the variability of undrained shear strength in clays. The two-dimensional spatial variation in soil undrained shear strength is modeled by random fields, which are discretized by the Covariance Matrix Decomposition method. The procedure for random finite difference method is presented. An illustrative example is employed to investigate the effect of soil variability. Particular attention has been paid to the situation that undrained shear strength increases with depth. The results demonstrate that ignoring the variability of undrained shear strength will result in overestimates of the tunnel face stability if the support pressure of the tunnel face exceeds the deterministic value, especially for higher coefficient of variation of soil undrained shear strength. Minor differences in the failure mechanism are observed in comparison to the deterministic case, considering only the global failure of the tunnel face is observed. In addition, ignoring the increase of undrained shear strength with depth will lead to conservative designs. The random finite difference method can provide a practical tool for evaluating the stability of a tunnel face in variable soils.

土壤特性的固有空间变异性被认为是岩土工程问题不确定性的主要来源之一。人们已经认识到需要对隧道面板稳定性进行概率分析，并考虑土壤性质的变化性。本文采用了一种基于概率的方法，即随机有限差分法，来评估黏土不排水抗剪强度变化对隧道工作面的稳定性。用不连续场对土壤不排水抗剪强度的二维空间变化进行建模，并通过协方差矩阵分解法将其离散化。给出了随机有限差分法的程序。一个说明性的例子被用来研究土壤变异性的影响。特别注意不排水的剪切强度随深度增加的情况。结果表明，如果不考虑不排水抗剪强度的变异性，则当巷道面的支护压力超过确定值时，会导致过高的隧道面稳定性，特别是对于不排水的土抗剪强度变化系数较大的情况。与确定性情况相比，观察到的破坏机制存在细微差异，仅考虑到了隧道工作面的整体破坏。另外，忽略不排水抗剪强度随深度的增加将导致设计保守。随机有限差分法可以为评估可变土壤中隧道工作面的稳定性提供实用工具。