砂土中盾构隧道开挖面失稳土体三维形状分析

合理确定盾构隧道开挖面前方失稳土体的形状是开挖面极限支护压力计算及开挖面失稳风险评估的基础和难点。建立模拟盾构隧道开挖面失稳过程的数值模型，利用Handy拱效应理论，依据Mohr-Coulomb破坏准则，得出失稳土体破坏位置和形状的计算方法。研究结果表明，水平方向由于隧道左右两端的支承作用产生水平压力拱，使失稳土体存在一个极限边界，极限边界内垂直方向的土体移动产生悬链线形的最小主应力拱，失稳土体形状类似贝壳形。以南京地铁3号线浦珠路站－滨江路站区间盾构隧道工程作为算例，理论分析和数值模拟结果吻合较好。

Three-dimensional shape of unstable soil of shield tunnel surface in sands

Reasonable determination for limit supporting pressure calculation and stability assessment of shield tunnel surface, it is basic and difficult to determine the unstable soil shape of shield tunnel surface. A numerical model is established to simulate the process of losing stability. According to the Mohr-Coulomb failure criterion, the Handy soil arching theory is used to get the calculation method determine the position and shape of unstable soil. The results show that the horizontal pressure arch is generated due to supporting effect of tunnel left and right sides in the horizontal direction, which causes that the unstable soil has a limit boundary. Catenary minimum principal stress arch is generated due to vertical soil movement in the limit boundary, the shape of unstable soil is similar to the shell-shaped. Taking the tunneling project of Nanjing Metro Puzhulu-Binjianglu section for example, theoretical calculation and numerical simulation results of the project are in good agreement.