Longitudinal and cross-sectional partitioned failure mechanism of tunnels subjected to stick-slip action of strike-slip faults
Permanent displacement occurs in strike-slip faults due to stick-slip action,causing significant damage and distinct partitioning features in tunnels intersecting these faults.To elucidate the longitudinal and cross-sectional partitioned failure mechanism of tunnels and provide seismic design support for tunnels intersecting active faults,we investigated several seismic damage examples to summarize three tunnel failure modes:circumferential cracks,inclined cracks,and longitudinal cracks.The key influencing factors,such as fault type,intersection angle,fault dislocation,and tunnel stiffness,were identified and discussed.The results show the following.1)The mechanical response and safety of tunnels are primarily influenced by fault type,while dip angle has a minimal impact;2)Tunnels subject to left-lateral strike-slip faulting can be longitudinally divided into bending-compression-shear(L-BCS)and bending-compression(L-BC)zones,while those subject to right-lateral strike-slip faulting can be divided into bending-tension-shear(L-BTS)and bending-tension(L-BT)zones;3)The range of the L-BCS and L-BTS zones is 1.4D-1.7D(D is the tunnel diameter),whereas the range of the L-BC and L-BT zones varies with key influencing factors;4)The cross section of tunnels can be divided into eccentric-compression(C-EC)and eccentric-tension(C-ET)zones,which are susceptible to eccentric compression or eccentric tension failure.The C-EC and C-ET zones are approximately 5D away from the fault plane;5)The C-EC zone of tunnels that traverse left-lateral strike-slip faults includes the left hance of the hanging wall,right hance of the footwall,tunnel crown,and tunnel invert,while the C-ET zone includes the left hance of the hanging wall and right hance of the footwall.In addition,the cross-sectional partitioning of a tunnel crossing a right-lateral strike-slip fault is symmetrical to that of a left-lateral fault.
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