浅埋隧道缓倾层状围岩变形破坏特征分析研究OA

To address the deformation and failure issues prone to occur after the excavation of gently inclined layered surrounding rocks in shallow-buried tunnels and ensure the construction safety,the Pingfengshan Tunnel was taken as the research object.Using 3DEC numerical simulation,the deformation and failure characteristics and mechanisms were analyzed under different rock stratum dip angles.Anchoring parameters were optimized by the control variable method,and an asymmetric anchor support scheme was proposed.Finally,the support effectiveness was validated through field monitoring.Results show that the gently inclined layered surrounding rocks of the Pingfengshan Tunnel have no risk of geological unsymmetrical pressure.Surrounding rock deformation is mainly dominated by shallow burial pressure and weak bedding plane effects;As the rock stratum dip angles increases,the deformation transforms from symmetric deformation to asymmetric slip dominated by weak bedding planes.Displacements concentrate on the left arch waist and the right sidewall along the bedding plane.The compressive stress on the initial support at the left arch waist increases with the increase of the rock stratum dip angle;The optimal anchor bolt parameters are 5 m length and 1.0 m×1.0 m spacing.The asymmetric support scheme involves lengthening the anchor bolts to 7 m and reducing the spacing to 0.8 m×0.8 m for the left arch waist and the right sidewall;Monitoring results show that after the on-site implementation of this support scheme,the maximum vault settlement was 24.40 mm,and the maximum convergence of both waists was 11.31 mm.After a rapid growth stage and a steady growth stage,the surrounding rock deformation tended to stabilize without obvious deformation or failure,verifying the effectiveness of the asym-metric anchor bolt support.These findings provide valuable engineering references for surrounding rock control and construction safety management in similar tunnels.