Stability Analysis of Surrounding Rock at the Entrance of Shallow Buried Biased Pressure Tunnel
The rock mass at the portal section of mountainous tunnels often presents challenges such as shallow burial,lateral pressure,and severe weathering,which increase the difficulty of tunnel construction and the risk of instability.Based on the Dayangyun Expressway's Daliangzi Tunnel project,the stability issues of the rock mass at the shallow-buried and biased tunnel portal section were investigated.A three-dimensional model was established using the finite element software Midas GTS/NX.A comparative analysis was conducted on three construction methods:the two-step method,the circular excavation with reserved core soil method,and the CD method.The goal was to determine the optimal construction approach and provide guidance for practical engineering.The results revealed that the deformation of the rock mass at the shallow-buried and biased tunnel portal section exhibited non-uniform characteristics,with larger deformation observed in the deeper-buried side.Significant sudden changes in deformation were observed on both sides of the weathering boundary line of the rock mass.Significantly larger deformation and influence range observed on the strongly weathered side compared to the weakly weathered side.The circular excavation with reserved core soil method exhibited better control over the stability of the rock mass,ensuring both tunnel and slope safety while saving time and manpower.Monitoring results demonstrated the effective control of rock mass deformation using this method,with deformation trends consistent with numerical simulation results,confirming the rationality and reliability of the analysis outcomes.
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