Three‑Dimensional Limit Equilibrium Solution of Minimum Support Pressure of Shield Tunnel Face in Sandy Cobble Stratum

摘要

The ground subsidence accident caused by the instability of shield tunnel face has been a major problem that puzzles urbansubway construction in weak rock. Maintaining the stability of tunnel face is the key to ensure the safety of shield constructionand reduce the environmental impact. In view of the shield with a diameter of 8600 mm in Chengdu metro line 18through the sandy cobble stratum, it is more difficult to maintain the stability of the shield tunnel face than other strata. Thecharacteristics of the sandy pebble stratum were taken into account firstly in this paper. The analytical equation was obtainedby the limit equilibrium method. The optimization of the trapezoidal bottom has been improved based on the existing 3Dtrapezoidal wedge model. And the optimal solution of the ultimate support pressure was obtained. The influencing factorsof support pressure are also analysed. When the tunnel diameter is fixed, the deeper the ground covering depth is, the greaterthe required limit support pressure becomes. But the ground covering depth has almost no effect on the ultimate supportpressure even if the tunnel is deep. The limit support pressure is inversely proportional to the internal friction angle of thesoil and is proportional to the diameter of the tunnel. Finally, theoretical limit support pressure can be also verified by thenumerical simulation results and the field monitoring results. It provides a reference for the subsequent setting value of thesoil warehouse pressure.