Study of Advanced Dewatering and Its Influence on Tunnel in Water Rich and Sandy Dolomite Stratum

The influence of groundwater on sandy dolomite stratum renders it highly susceptible to disasters, resulting in frequent water inrush accidents during tunnel construction. Advanced dewatering is crucial in enhancing tunnel face stability. It is found that sandy dolomite comprises a porous permeable medium consisting of dolomite sand and dolomite powder, characterized by low shear resistance and deformation resistance. Through the fluid–solid coupling model test device developed, it has been proven that the release of pore water pressure via advanced dewatering substantially enhances the stability of the tunnel face in water-rich sandy dolomite stratum prone to seepage failure. By conducting fluid–solid coupling analysis, the impact of drainage pipe length on the dewatering effect is investigated, and the improvement in tunnel face stability due to varying drainage pipe lengths is evaluated using the limit equilibrium analysis method. It is observed that drainage pipes reduce the range of slip body in front of the tunnel face and mitigate seepage forces by dissipating pore water pressure, consequently enhancing tunnel face stability and reducing extrusion deformation. However, there exists an efficiency limit regarding drainage pipe length. For initial water levels of 30, 50, 80, and 120 m, it is recommended to employ advanced drainage pipes of 20, 25, 30, and 40 m or more, respectively.