Study on Stability of Excavation Surface of Shield Tunnel in Clay Layer

If an excavation surface becomes unstable, it will cause damage such as soil collapse or surface uplift. Through field investigations and tests, the stability of the shield tunnel excavation surface and its influencing factors are studied in this paper. Equations for solving the limit support pressure of the excavation surface of the overlying multilayer soil tunnel and for the safety factor of the excavation surface are deduced. The single reduction method and the double reduction method are respectively used to solve the safety factor of the excavation face under the basic working conditions, and the numerical simulation method of the safety factor of the excavation face is clarified. Based on FLAC3D numerical simulation software, the ultimate support pressure and safety factor were used as the evaluation criteria for the stability of the excavation face to analyze the response of objective factors such as internal friction angle and cohesion, as well as engineering factors such as hole diameter to the stability of the excavation face. The greater the internal friction angle and cohesion, the smaller the hole diameter, the more stable the excavation surface, and the internal friction angle has the greatest impact on the stability of the excavation surface.