Instability Mechanism of Du Yun Pass Tunnel Entrance Weathered Stacking Area Analysis

The stability of the tunnel portal section under poor terrain and geological condition has always been the focus of construction safety. The stability problem has become more complex for the erosion accumulation area under the valley. In this paper, firstly the stability of the tunnel portal is classified. Combined with engineering cases, the FEM numerical method is used to simulate the supporting structure and construction process of the tunnel. Based on the distribution of the plastic zone and displacement of surrounding rock, the mechanism of the instability of the tunnel portal is analyzed. Through the optimized construction scheme that arranges pile foundation in tunnel arch foundation, the bearing capacity of foundation has been greatly improved, which has effectively prevented the instability of surrounding rock caused by the slope deformation and foundation settlement. The conclusions that have been drawn in this paper can be used for reference for related projects.