Deformation Analysis of Deep Soft Rock Tunnel Considering Deterioration Effect and Supporting Time

The surrounding rock deformation of the deep-buried soft rock tunnel was closely related to its parameter deterioration,rheological characteristics,and the timing of the supporting structure.The viscoelastic-plastic analytical formula of the surrounding rock in each support stage of the composite lining support structure was obtained based on the unified strength criterion using the mechanical model for the composite lining of the deep soft rock circular tunnel.This process was done while taking into account the deterioration of the strength parameters (cohesion,internal friction angle) and stiffness parameters (elastic modulus) of the surrounding rock in the plastic zone.Results indicate that the deformation obtained by properly considering the intermediate principal stress and the degradation effects of parameters of the surrounding rock is in better agreement with deep soft rock tunnel deformation.The residual cohesion,residual internal friction angle,and residual elastic modulus of the surrounding rock significantly affect the instantaneous and late creep deformation of the surrounding rock and the resistance of the secondary lining,where a lower value indicates more significant deformation.Furthermore,increasing bolt length,decreasing bolt spacing,and increasing initial support thickness can effectively control the instantaneous deformation and late creep deformation of the surrounding rock.The application time of the secondary lining significantly influences the late creep deformation of the surrounding rock.The late creep deformation of the surrounding rock can be effectively controlled by applying a secondary lining as soon as possible after the instantaneous deformation of the surrounding rock.