Study On Dynamic Response Mechanism And Flexibl Lining Stucture Of Mountain Tunnel Crossing Fault Under Earthquake

The dynamic analysis and design of tunnel structures crossing faults are inevitable issues in tunnel engineering construction in high seismic intensity areas.The key to enhance the aseismic capability of fault-crossing tunnels in the complex and mountainous areas is to make clear their dynamic response mechanisms and to adopt the appropriate aseismic measures.Supported by the National Natural Science Foundation of China(NSFC)(Nos.51678501 and51778540)and the Chunhui Program of the Ministry of Education entitled "Design of shock absorption joints and evaluation of comprehensive index on seismic resistance and shock absorption performance of materials for fault-crossing tunnels",and based on the investigation results of earthquake damage of fault-crossing tunnels,the relevant engineering geological data are collected and analyzed.Afterwards,based on the vibration theory,the mechanism of transverse and longitudinal dynamic responses of the fault-crossing tunnels are studied and the engineering suggestions are put forward.Finally,the flexible structure of tunnel lining coping with fault dislocation is developed and its rationality and advancement are evaluated,and then the mechanical parameters of the simplified members are obtained.The main work,conclusions and achievements of the research are clarified as follows:(1)Based on the geological data and seismic damage data of 8 fault-crossing highway tunnels in the Wenchuan earthquake,the effects of faults on seismic damage of the tunnels are evaluated in detail.In view of the influences of faults on the seismic damage of tunnels,statistical analysis is developed on the characteristics of 254 faults in the design and construction data of more than 150 tunnels in 5 lines built and under construction.The results show that the seismic damage of tunnel structures under the influences of faults is predominantly relevant to fault dislocation,fracture zone width,intersection angle between fault and tunnel axis,fault dip angle,fault lithology,the difference of seismic intensity and fortification intensity,etc.However,there is no correlation among the components of fault characteristics.Under complex geological conditions and earthquake action,seismic responses of tunnel structures crossing-faults are as follows: first,the forced displacement of fault dislocation exceeds the scope of shear deformation;second,the weak surrounding rocks in the fracture zone and the affected area result in the disharmony between surrounding rock and lining structure deformation under earthquake action;third,when the width of the fracture zone and the affected area is large,the axis of the tunnel can be forced to change.In this research,based on the statistical data,the earthquake damage investigation results and the existing research,the formula for calculating the length of fault-affected range is revised.(2)Based on the vibration theory and the above research,the relative displacement analysis model of the transverse dynamic response of tunnel structure is established,and the theoretical solution of the model is given by the Zhai method.In order to analyze the results of the model test,the calculation parameters are established on the basis of the model test and solved by the established theoretical model,and the calculated results show that the relative displacement of the surrounding rock in the plastic zone and the lining under the action of 0.4 g shear seismic wave is 10 times the allowable radial deformation of the tunnel structure.The numerical simulation of the model test is carried out by using the Universal Discrete Element method.The results of the simulation agree well with the earthquake damage phenomenon of shaking table test,and the monitoring data agree well with the calculated results of the proposed relative displacement model.The investigation of tunnel seismic damage and the study of dynamic response show that the dynamic response of lining structure has the following,dependence and lagging effects to surrounding rock,and the model analysis and numerical calculation indicate that the relative displacement between the surrounding rock in the plastic zone and the tunnel structure is the primary cause of the damage of the lining structure.The relative displacement between the surrounding rock in plastic zone and the lining structure can be directly solved as a quantitative index for the dynamic response evaluation of the lining structure.The results provide a new method for transverse dynamic response analysis of fault-crossing tunnel structures.(3)Based on the vibration theory and the transverse dynamic response analysis model,the relative displacement analysis model of longitudinal dynamic response of fault-crossing tunnel is proposed.The dynamic response of surrounding rock and lining structure under fault dislocation and earthquake is analyzed by the Zhai method,and the longitudinal relative displacement is obtained as the dynamic response evaluation index.The analytical solution and numerical calculation of the vibration theoretical model verify the model test.Weakening the longitudinal joint stiffness of the lining is conducive to reducing the relative displacement of structure between the active wall of the fault and the fracture zone,but unfavorable to the tunnel structure between the fixed wall of the fault and the fracture zones.Reducing the length of the lining structure segment located in the active wall of the fault is conducive to resist the fault movement compared with its disadvantage to seismic dynamic action.The lining structure located in the fixed wall of the fault can withstand the fault dislocation and the earthquake dynamic action if the lining structure segment is divided appropriately.The partition formulas of lining segment length in fixed wall of the fault and active wall of the fault wall are presented.The above research provides the theoretical support for the structural analysis and design of the fault-crossing tunnel.(4)A new type of flexible lining structure for fault-crossing tunnel is developed,and its mechanical parameters are given.Comparing the performance of new-type flexible structure with that of conventional lining structure,the experiment of mechanical performance of simplified members of lining structure is carried out,and the relevant mechanical parameters are measured.The large eccentric bending test demonstrates that the new type of flexible structure has higher ultimate bearing capacity and greater self-deformation capacity than the conventional structure.The impact test illustrates that the failure patterns of the structure vary a lot under the impact,and the energy is always dissipated along the part where the structure is more readily displaced and deformed.Under the guidance of the seismic response mechanism of the fault-crossing tunnel,the mechanical parameters demonstrate that the flexible lining structure is superior to the conventional lining structure.The above research results can provide insights into the further study on seismic damage mechanism of fault-crossing tunnel.