Study On Tunnel Disaster Response Mechanism And Disaster Range Prediction Under Active Fault Dislocation

In recent years,with the gradual advancement of "The Belt and Road" policy in China,the transportation industry in the southwest region has entered a new period of rapid development,and the construction of the Sichuan-Tibet Railway has also become the focus of transportation construction.There are relatively numerous mountains and plateaus in the southwest of China.Tunnel has become a significant engineering construction to connect two regions.The construction of tunnel will become an important method to promote transportation and economic development,as well as a connecting link to expand regional communication.However,due to the particular geographical location of southwest in China,the movement of the plate leads to frequent earthquakes,and the geological conditions are complex,and the active fault zones are widely distributed.The dislocation of active faults will lead to serious damage or even fracture of the tunnel structure.The design,construction,disaster prevention and mitigation,and post-monitoring of tunnels crossing active faults have become one of the problems that researchers need to solve urgently.Based on the Kangding No.2 Tunnel,this paper adopts a combination of model test,numerical simulation and theoretical analysis according to the actual survey data.A systematic study is carried out on the failure mechanism of the tunnel structure under the fault dislocation of different forms,different dip angles,different speeds and different dislocations.The specific research content and research results are as follows:(1)Based on the research on rock mass cracking and tunnel structure damage under strike-slip/reverse fault dislocation,this paper independently designs and develops model test device that can simulate strike-slip fault,reverse fault and strike-slip-reverse fault dislocation under the condition of different forms,different dip angles,different speeds and different dislocations.(2)According to the survey data of the actual project and adopt the self-developed tentative device,this paper carried out an interior model test with a similar ratio of 1:50.Through the test,the deformation distribution,the interaction pressure between surrounding rock and lining and vertical strain development and lining crack extension under different dislocation methods,different inclinations and different velocity of faults can be researched.The damage methods of lining under different conditions can be compared and analyzed,and finally the mechanical characteristics and destruction mechanism of the tunnel lining structure can be revealed.The damage of the tunnel lining under the strike-slip/reverse fault is mainly concentrated in the fracture zone area and the cracks gradually extended with the increase of dislocation.The damage of lining under reverse fault of different inclinations show a obvious upper effect,that is,the crack extension and damege of the upper section on the fault is obvious than that of the footwall.The damage degree of reverse fault varies with different inclinations,the cracks of upper wall lining under 90 ° reverse fault dislocation is the most obvious,and the crack extension of 70 ° reverse faulti s the longest,and the crack can extend to the footwall of the fault to form full penetration failure.(3)This paper utilizes the finite element analysis software ABAQUS to establish a three-dimensional finite element model.The accuracy of the three-dimensional finite element model of the built-in slip/reverse layer is verified based on the physical model test,and based on this,a three-dimensional finite element model of tunnel failure under strike-slip-reverse coupling fault dislocation is established.In this paper,the deformation distribution characteristics,the maximum principal stress distribution characteristics and variation laws,the shear stress distribution along the load application direction,the plastic zone and the variation laws of plastic strains of the tunnel structure under different inclination angles and different dislocation effects are studied.The research results show that the damage range of tunnel lining under coupling fault dislocation is mainly concentrated in the area near the fracture zone.The failure range is related to the fault dislocation momentum at the beginning of the fault dislocation,and the final failure range is negatively related to the dip angle of the fault zone.Under the coupled fault dislocation,the plastic zone of the tunnel lining is mainly concentrated in the vault and the right arch waist,and these two parts are tension zones,and the damage of the tunnel lining is mainly tension damage.(4)Combined with the actual survey results of the Kangding No.2 tunnel and the width of the equivalent plastic zone of the tunnel lining under reverse fault dislocation,the least squares method is used to study the correlation between the dip angle of the fault zone and the extent of the tunnel lining plastic zone under reverse fault dislocation in this paper,and the main influencing factors and derivative influencing factors could be obtained.Taking the influencing factors as input parameters and the equivalent plastic zone width of the tunnel lining as the output result,GA-BP neural network and GRNN were used to establish prediction models to predict the damage range of the tunnel.The results show that: GA-BP neural network is slightly less predictable than GRNN but has better stability,while GRNN has better predictability,but is slightly less stable because only one parameter needs to be determined.