浅埋大直径盾构隧道开挖面局部破坏的被动稳定性研究

Study on Passive Stability of Tunnel Faces in Shallow Large Diameter Shield Tunnels Considering Partial Failure

浅埋盾构隧道施工时开挖面极易发生被动破坏,而大直径盾构隧道开挖面的被动破坏更为复杂。利用极限分析上限法建立浅埋大直径盾构隧道开挖面被动稳定性分析的二维破坏机制,该机制考虑了仓内土压梯形分布和仰拱上方处开挖面局部破坏的影响,并提出开挖面局部被动破坏时的极限支护压力上限解。通过对计算结果的参数分析发现,无黏性土的开挖面极限支护压力是土体有效内摩擦角φ^(′)和归一化无量纲参数埋深比C/D的函数,同时φ^(′)和C/D对开挖面局部被动破坏的起点位置存在影响;而黏性土的开挖面极限支护压力是φ^(′)和C/D以及有效黏聚力c^(′)的函数,但是有效黏聚力c^(′)对极限支护压力的影响要小于φ^(′)和C/D的影响。将本文与已有上限解进行对比,验证了本文所提上限解的有效性,结果表明,本文的上限解能够预测开挖面任意深度处的局部被动破坏的通解,而已有上限解只是假定开挖面发生全局被动破坏的特解。最后,结合实际工程验证上限解的合理性,该计算方法能够合理评价浅埋大直径盾构隧道开挖面的被动稳定性。

The passive failure of tunnel faces is easy to occur during shallow shield tunneling.The passive failure of large diameter tunnel faces will be more complicated.This paper established a 2D passive failure mechanism of shallow large diameter tunnel face using upper bound analysis.The upper bound solution of ultimate support pressures considering the trapezoidal chamber pressures and the partial failure is derived.For cohesionless soils,the ultimate support pressure is a function of effective frictional angle φ~′ and the normalized dimensionless parameter buried depth ratio C/D.Meanwhile,φ~′ and C/D have an impact on the starting point of partial passive failure.For cohesive soils,the ultimate support pressure is a function of φ~′,C/D,and the effective cohesion c~′.However,c~′ on the ultimate support pressure is less than φ~′ and C/D.The mechanisms are verified by comparing the current solutions with a previous upper bound solution.The result shows that the current solutions are general solution that can predict the passive failure originating at any depth along tunnel faces and the previous solution is a particular solution.Finally,the upper bound solution is validated through application to a practical engineering.The validation shows that the method can rationally assess the passive stability of tunnel faces.