Probabilistic Seismic Risk Analysis Of Tunnels Under The Active Fault Dislocation

As an essential part of lifeline engineering,tunnels are the hub of transportation.With the development of economy,the society demands more and more for them.As a long linear structure,the tunnel will inevitably pass through active faults during the construction process.Known from its history,subway stations or tunnels crossing the fault will suffer severe damage due to fault dislocation when an earthquake occurs.It will be challenging to repair those damages after the disaster,and substantial economic losses will be induced.However,the current research on the seismic risk analysis and assessment of tunnels mainly focuses on the tunnel damage risk caused by ground motion.Moreover,quantitatively determining the tunnel damage risk caused by the fault dislocation during the earthquake still needs to be solved urgently.This thesis proposes a full probabilistic analysis method for seismic risk analysis of tunnels crossing active faults based on finite element simulation and systematically analyzes the structural response characteristics of the tunnels.The seismic risk analysis framework includes fault dislocation risk analysis,structural response analysis of tunnels due to fault dislocation,fragility analysis,and probabilistic seismic risk analysis.The analysis framework can be used for seismic risk assessment of tunnels crossing active faults,and it can also provide some suggestions for the anti-fault design of tunnels crossing active faults.(1)Based on the PBEE method,a full probability seismic risk analysis method based on finite element simulation is established for tunnels crossing active fault.This method can quantitatively evaluate the seismic damage risk level of tunnels crossing active faults due to fault dislocation.(2)The relationship between strike-slip fault bedrock dislocation and magnitude is established by collecting historical seismic damage data and using statistical regression analysis methods.Based on this relationship,seismic hazard curves of bedrock dislocation of the strike-slip fault are obtained.(3)Based on the three-dimensional tunnel modeling by finite element software ABAQUS,the structural responses of the tunnels due to the bedrock fault dislocation are calculated by considering five factors,including fault-tunnel crossing angles,bedrock overburden thickness,tunnel buried depth,lining thickness,and soil properties.The influence of various factors on the structural response of the tunnels is then discussed.The damage index,i.e.,bending moment ratio,is used to classify the damage states of the tunnels.The structural fragility function of the crossing-fault tunnel is established,and the fragility curves are then obtained.(4)Based on the seismic risk analysis proposed in this paper,the seismic risk considering the five influence factors is assessed and compared.The influence of the five factors is discussed on the probabilistic seismic damage risk and the probability of reaching a limit state in the return period for the tunnels.The obtained results can provide a reference for the anti-fault seismic design and assessment of tunnels crossing faults.Finally,an engineering example is given to demonstrate the application of the seismic risk analysis method proposed in this paper for crossing-fault tunnels.