Study On Mechanical Response Of Metro Tunnel Lining Structure Crossing Active Ground Fissure

Ground fissures are a typical urban geological hazard,and their complex genetic mechanisms and slowly changing activity characteristics bring great safety hazards to the construction of urban metro projects.Xi’an is located in the Fenwei Basin,and due to the coupling effect of tectonic control and groundwater extraction,the hazards caused by ground fissures is very prominent,and some ground fissures still have certain activity.Therefore,it is of great theoretical and practical significance to reveal the interaction mechanism between tunnel and stratum within the ground fissure environment and the mechanical response of tunnel lining structure under the action of ground fissure activity for the design and safe operation of Xi’an Metro.This paper analyzes the mechanical mechanism of the interaction between strata and tunnel caused by ground fissure activity based on the uneven settlement deformation and stress transfer law of strata in the environment of ground fissures.It elucidates the process of stress changes in the overburden strata caused by ground fissure activity,and studies the mechanical response of tunnel lining structures across ground fissure zones,targeting two types: ground fissure dislocation and seismic force.The main research findings include:(1)The laws of strata displacement and stress field changes under ground fissure activity were revealed,and the basic mechanical models of ground fissure activity induced by two types of actions,namely deep bedrock fault activity and extraction of underground confined aquifer,were explored.This provides a basic mechanical background for the study of the interaction mechanical mechanism between strata and underground structures in the ground fissure site.(2)Based on the interaction between the strata and the tunnel lining,the longitudinal load distribution pattern of the tunnel was elucidated,and the stress changes in the overburden strata of the tunnel under the action of ground fissures were divided into three stages,including the initial elastic stage,local void area stage,and maximum void area stage.Based on the stress characteristics of each stage,a corresponding simplified calculation method was proposed to reasonably determine the vertical strata stress of the tunnel lining in the ground fissure site.(3)Based on the Vlasov foundation model,the tunnel was considered as a Timoshenko beam considering shearing action.An analytical solution was established for the longitudinal mechanical behavior(including deformation,rotation angle,bending moment,and shear force)of the shield tunnel under the additional load caused by ground fissure activity,providing a theoretical basis for the structural design of shield tunnels in the ground fissure site.(4)The effect of seismic load on the dynamic response of tunnels crossing the ground fissure zone was considered,and the tunnels in the strata were viewed as shear beams of Kelvin viscoelastic foundation.According to the Green’s function of steadystate dynamic response,the structural dynamic response law of tunnels was analyzed by using Laplace transform formula and residue method,which provides a reference for the seismic design of metro tunnel lining structures in the ground fissure field.