梅子岭浅埋小净距大断面隧道施工稳定性与优化OA

In the hilly and low-mountain regions of eastern China,shallow-buried,small-clearance,large-section tunnels passing through composite grade Ⅳ and Ⅴ surrounding rocks face high construction risks.The shallow rock mass is extensively weathered and severely fractured,with densely developed fissures throughout,rendering tunnel excavation face highly vulnerable to structural instability,localized deformation,and even partial collapse during construction.Such risks pose serious threats to construction safety and the smooth progress of tunnel project,making tunnel excavation under these conditions become one of the most hazardous stages.To address the issue of selecting suitable construction method parameters under these weak rock conditions,this study combines extensive field measurements with numerical simulation analysis.By comparing different excavation methods and construction control parameters,this study systematically investigates their effects on surrounding rock deformation,specifically focusing on ground surface settlement,arch crown settlement,and lateral wall horizontal displacement.The deformation patterns and underlying mechanisms are comprehensively revealed.The results show that,for the initial entry and exit sections of Meiziling Tunnel in grade Ⅴ surrounding rock,the double-side pilot tunnel method is more appropriate.This method effectively reduces the exposed area of rock,distributes stress more evenly,enhances support system stability,and minimizes collapse risk.In contrast,for the sections transitioning into grade Ⅳ surrounding rock,the single-side pilot tunnel method is more suitable,as it better aligns with the mechanical behaviours of surrounding rock and reduces construction-induced disturbance.Additionally,the step height in bench excavation significantly affects tunnel deformation control.Considering construction safety,efficiency,and schedule constraints,it is recommended that upper step height should not exceed 4 m in this project.Moreover,under grade Ⅴ and Ⅳ rock conditions,the face offset distance in twin-track tunnel construction must be carefully designed to avoid interaction between adjacent excavation faces and prevent cumulative deformation.The reasonable displacement of working face should not be less than 2B and 1.5B for Class Ⅴ and Ⅳ surrounding rock conditions,respectively.This case study provides a valuable reference for the successful implementation of shallow-buried,small-clearance,large-section tunnels in the eastern China,particularly those encountering composite grade Ⅳ and Ⅴ surrounding rocks.