考虑砂土抗剪强度空间变异性的盾构开挖面稳定性分析

采用传统研究方法对盾构开挖面稳定性的分析多基于土体是均质、各向同性材料的假设，显然与其本身的非均质性相违背。为此，开展了考虑土体抗剪强度参数的空间变异性对盾构开挖面稳定性的影响研究。在随机场理论的基础上，采用协方差矩阵分解法建立了描述砂土内摩擦角空间变异性的三维随机场模型，借助于数值分析软件平台研究了内摩擦角的变异系数、自相关距离对开挖面失稳模式、极限支护应力的影响规律，并采用概率分析法探讨了极限支护应力特征值的选取。结果表明：砂土内摩擦角的空间变异性对开挖面稳定性有重要的影响；随内摩擦角的变异系数的增大，极限支护应力的概率分布离散性越大；开挖面失稳模式与自相关距离的大小密切相关，当自相关距离与隧道直径比较接近时，开挖面可能出现局部失稳；提出了开挖面极限支护应力特征值的概念，并结合失稳概率给出了其初步确定方法。

Face stability analysis for a shield tunnel considering spatial variability of shear strength in sand

The conventional analysis methods for face stability of shield tunnels always assume that the soil is homogeneous, isotropic medium, and ignore its heterogeneity. Therefore, the influence of spatial variability of shear strength on face stability in sand is investigated in this paper. Based on random field theory, three dimensional random fields of friction angle are generated using the covariance matrix decomposition method. The performance of the coefficient of variation and the auto-correlation distance of friction angle is analyzed to explore the influence of that on the failure mechanism and the critical support pressure. Meantime, the selection of the characteristics value of critical support stress is discussed by probabilistic analysis approach. Results show that the spatial variability of friction angle does have significant influence on the stability of tunnel face. The critical support stress scatters as the coefficient of variation of friction angle increases. The failure mechanism is closely related to the auto-correlation distance. When the auto-correlation distance is close to the tunnel diameter, the local failure may happen. The concept of characteristics value of critical support stress is proposed and defined preliminary based on the probability of failure.