Stability Evaluation Model of a Tunnel Face Excavated by the Benching Method in a Soft Silty Clay Layer

Abstract With the increasing construction demand for tunnels in soft silty clay layers, it is important to effectively control the face stability of a tunnel. One of the key issues for maintaining face stability is addressing how to accurately obtain the limit support pressure of a tunnel face excavated by the benching method in a soft silty clay layer. Therefore, based on the limit equilibrium method, an improved three-dimensional face stability analysis model is presented in this paper considering the advancing support effect of small pipes. In the model, the sliding failure zone is formed by a log-spiral line. The upper load of the sliding failure zone is shaped by the gravity of the soil, and it can be calculated by a two-parameter elastic foundation beam model when an advanced small pipe is utilized. By comparing these results with the limit support pressure predicted by existing models, the improved model is shown to be reasonable. Finally, the influence of the soil parameters on the limit support pressure is also assessed. The proposed failure mechanism improves the stability analysis of the tunnel face excavated by the benching method in the soft silty clay layer.