Face stability analysis of cohesion-frictional soils considering the soil arch effect and the instability failure process

Abstract

Based on the limit equilibrium method, a new three-dimensional progressive failure model, which includes the upper loose zone and the lower slip zone, is proposed to analyze the stability of a tunnel face. In the model, the ellipsoid of the upper loose zone is discretized into a plurality of frustums. Considering the soil arch effect, the theoretical solution of loose earth pressure under an arbitrary slip surface dip angle is calculated iteratively based on the principal stress rotation theory. The limit support pressure of the three-dimensional failure model is obtained. Then, the accuracy and effectiveness of the new model are verified by comparison with existing model tests and theoretical methods. Finally, the effect of the soil parameters on the limit support pressure is discussed. The relation curve between the loose zone height and the support pressure is determined. The instability failure process of the tunnel face is analyzed. The results show that the internal friction angle and cohesion have significant effects on the limit support pressure. The tunnel face instability failure process is defined. As the height of the loose zone increases, the limit support pressure decreases sharply first, then increases slowly, and finally reaches a fixed value.