Prediction and analysis on large deformation of surrounding rocks in the Muzhailing Tunnel of the Weiyuan–Wudu Expressway under high in-situ stress

This study aims to solve the significant deformation issue in the soft surrounding rocks under high in-situ stress encountered during the construction of the Muzhailing Tunnel on the Weiyuan–Wudu Expressway. We established a three-dimensional geological model to invert the in-situ stress field using ANSYS based on measured in-situ stress data in the engineering area. Then, we calculated and analyzed the deformation of the surrounding rocks by combining the inverted results with the Hoek deformation prediction formula. The result showed that the in-situ stress field in the engineering area was primarily controlled by faults, with secondary influences from rock strength and topography. In the intense tectonic deformation zone, horizontal principal stress values are generally lower than in the weak structural deformation zone. The relationship between the three principal stresses along the tunnel axis is SH>Sh>SV. The maximum horizontal principal stress in the intense tectonic deformation zone was the highest in the G8 section and the lowest in the G6 and G11 sections. In the weak structural deformation zone, horizontal principal stress gradually increases from the G12 section until it decreases due to reduced burial depth starting from the middle of the G14 section. The maximum horizontal principal stress orientation was generally in the NE direction, and the extruded structural belt between the faults was mostly deflected to the NEE –nearly EW direction. The deformation of the surrounding rocks was affected by rock mass strength and in-situ stress field, with rock mass strength playing a dominant role. The deformation of the surrounding rocks is mainly concentrated in the range of 20 to 80 cm, and the deformation levels are mainly moderate and intense