Optimization of the Design and Construction Scheme of Tunnel Entry and Conversion System for Removal of Anti-slide Pile in Architecturally Sensitive Area

A tunnel excavation scheme analysis is conducted by using the Yangguang Tunnel in Panzhihua, and the conversion system is proposed based on the stressing characteristics of surrounding rock and structure during removal of anti-slide pile. The fine calculation model for tunnel excavation process has been created, the deformation response characteristics of surrounding rock, tunnel and building corresponding to different construction methods have been investigated, the study on scheme optimization has been conducted by taking into account the indicators including safety, economic efficiency, feasibility and duration, and field test and demonstration have been completed.The results indicate: under the effect of the conversion system in "counterfort retaining wall + anti-slide pile" composite structure, the surrounding rock-structure displacement is effectively inhibited and overall stability is maintained; compared with CRD method, reserved core method will generate more obvious mechanical disturbance, with maximally 40% difference between the two, but both construction methods meet the requirements for the displacement of stratum, conversion structure and building; during excavation for removal of anti-slide pile in tunnel, the stratum mainly experiences vertical displacement, the conversion system shows the most obvious response right at the pile cutting position, and the existing building is slightly inclined towards the tunnel side; in the original construction construction method, the CRD method generates less mechanical disturbance, but comes with high engineering cost, high technical difficulty, complex process and long duration. After a comprehensive comparison, the reserved core method is selected. According to field survey, the selected scheme is rational and brings desirable construction results in the project.