Study On Seismic Response And Applicability Of Anti-seismic Structure Of Tunnel Crossing Active Fault

The geology of the mountainous areas in China western is complex,and the seismic fault zone is very frequent.With the rapid development of traffic and water conservancy construction in the west,there are more and more tunnels crossing the fault zone of strong earthquake activity.Earthquake damage has shown that tunnels across active faults are prone to severe damage under the combined action of ground motion and fault movement,endangering structural safety and the smooth flow of lifeline projects.Therefore,it is of great practical significance to carry out research on the seismic response mechanism and anti-vibration measures of tunnels crossing faults.It is also an engineering problem that needs to be solved urgently in the construction of tunnels crossing active faults.Aiming at the current situation of research on the applicability of combined anti-seismic measures and improving the anti-seismic performance of the lining itself in the existing fortification systems of anti-seismic structures,this paper relies on a tunnel project in Yunnan Province that crosses the Xiaojiang active fault zone.On the basis of wrong anti-vibration prevention and control measures,high-performance ECC materials are introduced,and indoor tests and numerical simulations are combined to carry out research on seismic damage behavior of cross-fault tunnels,and the anti-vibration performance and applicability of conventional and new materials anti-vibration structures.Provide a reference for the structural design of tunnels crossing active faults.The main research content and related conclusions are as follows:(1)Based on a cross fault tunnel of geqiao expressway,a three-dimensional seismic response calculation model is established,and the simulation analysis of seismic response and damage behavior of tunnel structure under transverse earthquake with different strength is carried out.The results show that the lining is mainly damaged in tension,and the rapid increase of damage occurs in the period of 10 s before and after the peak of seismic acceleration.From the cross section of the tunnel,the stress at the foot of the wall is the most unfavorable,and the damage is the most serious;from the axial view of the tunnel,the lining damage is mainly concentrated in the fault fracture zone and adjacent areas.Moreover,the annular damage area of full section appears at the intersection of fault contact surface and lining,which shows obvious earthquake dislocation effect.The displacement,stress and damage degree of tunnel structure increase rapidly with the increase of seismic intensity.When the seismic peak acceleration is 0.4g and 0.6g respectively,the damage range of lining in the latter is 3 times and 2 times of that in the former.(2)Combined with the engineering fault and structural characteristics,the seismic response analysis of tunnel structure under three single damping measures and their combination are carried out,and the damping mechanism of single and combined measures is obtained.On this basis,the applicability of the combined measures is discussed.The results show that both the damping joint and the flexible joint can prevent the longitudinal expansion of the lining damage,reduce the damage distribution range and make the lining damage localized.With the decrease of the distance between the damping joint and the flexible joint,the adaptability of the overall deformation of the lining is enhanced,the deformation under the seismic action is reduced,and the overall seismic damage degree is also significantly reduced.However,the stress concentration at the end of the lining segment is intensified,and the local damage value is increased.When the damping layer is set,the seismic response of the structure is reduced,and the stress concentration and damage degree in the fault area are all reduced.With the increase of damping layer thickness and the decrease of stiffness,the deformation and stress of lining decrease,and the damage degree also decreases.The combination of damping joint and damping layer,flexible joint and damping layer shows better anti damping effect than single measure,and the damage reduction of lining is more than 50%.In the two combination measures,the combination of damping joint and damping layer has better anti damping effect.The incident direction of seismic wave has an important influence on the damage and anti seismic effect of tunnel structure under combined measures.Under the transverse earthquake,the lining is more affected by the fault dislocation,and the local damage is serious at the fault dislocation surface;under the longitudinal earthquake,the lining is subjected to the axial tension and compression earthquake,the lining damage in the fracture zone is aggravated,and the overall damage degree of the lining is more serious.The combination of anti seismic measures has better adaptability to lateral ground motion.(3)Based on the ECC uniaxial tensile and compression tests,the ECC tensile and pressure properties and parameters were determined.Based on the existing research results,the ECC damage constitutive model was constructed.According to the number of R/ECC(reinforced ECC)segments instead of traditional RC(reinforced concrete)segments in the tunnel,a seismic response calculation model of structure considering R/ECC,damping joint and RC combination is established,and the seismic response effect of different support combinations is compared and analyzed.Based on the above,combined with the measures of the seismic layer prevention and control,the R/ECC composite supporting structure of the cross fault tunnel is proposed.The applicability of the composite structure under different directions and different intensity earthquake actions is discussed.The results show that ECC has excellent tensile and compressive toughness,which can effectively improve the brittleness and energy consumption capacity of traditional concrete.The R/ECC lining is set in the fault fracture zone and near the fault fault fault moving surface,which can effectively reduce the damage degree and distribution range of tunnel lining structure,and has better anti vibration effect.The larger the R/ECC lining setting range,the lower the overall damage and failure degree of the tunnel lining under the same ground vibration strength.The damage degree and distribution range of R/ECC composite support structure are obviously smaller than that of traditional composite support structures with different ground motion incidence direction and strength,which shows excellent anti shock absorption performance and strong applicability.