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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。
Reasonably determining the shape of unstable soil in front of the shield tunneling surface is the basis and the difficulty of the calculation of the limit support pressure and the risk assessment of the instability of the excavation face. A numerical model is established to simulate the instability process of shield tunneling surface. According to the Mohr-Coulomb failure criterion and the Handy arch effect theory, the calculation method of the failure location and shape of the unstable soil is obtained. The results show that horizontal pressure arch occurs in the horizontal direction due to the support effect at the left and right ends of the tunnel, so that there exists a limit boundary of the unstable soil. The vertical soil movement within the limit boundary produces the catenary minimum principal stress arch, Body shape similar to the shell-shaped. Taking the project of shield tunnel of Pu Zhu Road Station - Binjiang Road Station in Nanjing Metro Line 3 as an example, the theoretical analysis and numerical simulation agree well with each other.