Coupling Static-dynamic Test Method And Seismic Safety Evaluation Method Of Cracked Tunnel Lining

Lining cracks are the most common tunnel anomalies,which are frequently regarded as one of the indicators of tunnel safety.Cracks bring leakage,carbonization,and corrosion to the concrete structure,and even destroy the structural integrity,leading to spalling and collapse.The seismic performance of operational tunnels in seismically active areas is very important.Therefore,it is not only necessary to pay attention to the safety of cracked lining under static load,but also to analyze and evaluate its safety under seismic load.In this paper,based on the engineering investigation,the response mechanism,structural damage evolution,and seismic safety of the cracked lining tunnel under the earthquake were studied by the model test and numerical simulation.The basic study methods and safety evaluation methods were also improved.The main study results and conclusions are as follows:(1)A coupling static-dynamic shear model box was developed,which had realized the coupling simulation of static and dynamic stress field in the process of shaking table model test.The model box has solved the problem that the rigid model box with flexible energy absorbing boundary may cause the distortion of self-weight stress field due to the insufficient rigidity of the side wall of the model box under static condition.The model box has also solved the problem that the stress and deformation of soil in the laminated shear model box are discontinuous under dynamic condition.The model box can provide adjustable boundary stiffness and damping,and realize the static dynamic coupling of vertical loading to simulate different geological conditions and buried depth conditions.The test results showed that the transverse boundary of the new model box can better simulate the propagation of seismic wave in the semi-infinite soil,effectively eliminate the influence of the reflection of seismic wave on the test results,and better simulate the shear deformation of soil under the shear wave.(2)A pseudo-static test method for seismic response of tunnels was proposed.Based on the new model box,combined with displacement loading system,this method can apply low cycle reciprocating shear deformation to the soil in the box through the displacement control of the transverse boundary of the model box to simulate the effect of shear wave on the tunnelsoil system.This method can get rid of the dependence on large-scale test equipment such as vibration table,reduce the test cost,and control the test process more flexibly.(3)A shaking table test and a pseudo-static test were conducted to study the dynamic response characteristics of the cracked lining tunnel under the action of seismic shear wave.The results were as follows: 1)The failure of the shallow tunnel was controlled by tensile stress,and the failure mode was mainly tension crack.2)The failure of the deep-buried tunnel was controlled by compression stress,and the failure mode was mainly collapse.3)The position of the spandrel and the wall foot of the lining structure had the strongest response to the seismic shear wave,and the longitudinal initial crack at the spandrel had the greatest impact on the seismic capacity of the lining structure.4)The initial crack section had little influence on the seismic peak bearing capacity of the tunnel,but the inclined section crack would cause the deformation speed of the lining structure to increase after the damage.5)The results of pseudo-static test and shaking table test were in good agreement.The results of model test can provide guidance for the analysis and research of numerical simulation.(4)A modified deformation-based pseudo-static analysis method for seismic response analysis of tunnels was proposed.This method can consider the nonlinear response of tunnel lining structure and surrounding rock and the interaction between them.The method can also consider the relatively complex horizontal stratum conditions and the initial stress state of the tunnel lining structure.Compared with the time-history analysis method,this method can ensure the accuracy of the calculation results and greatly reduce the calculation workload.(5)A set of seismic safety evaluation method of tunnel was established,which was based on strength reduction method and damage analysis evaluation method.This method can comprehensively evaluate the overall stability of tunnel-soil system and the micro damage evolution of lining structure.The plastic zone transfixion was selected as the instability criterion of the pseudo-static strength reduction method,which avoids the change of the key points of the analysis object,the difficulty of catching the sudden change of displacement,and the influence of the model and the finite element solver on the convergence of numerical calculation.In the damage evolution analysis,based on the hypothesis of strain compatibility and strength equivalence,an equivalent plastic damage constitutive model of reinforced concrete was proposed for damage analysis of tunnel lining structure,and the corresponding damage variables were also given.This constitutive model can accurately reflect the whole mechanical behavior and damage evolution process of reinforced concrete structure.(6)Based on ABAQUS finite element numerical analysis platform,2D and 3D numerical models of Dazhou-Chengdu railway tunnels were established.The strength reduction method and the damage analysis and evaluation method were used to analyze the seismic stability and structural damage evolution process of the cracked lining tunnel under the action of seismic shear wave,and evaluate the seismic safety comprehensively.The simulation results showed that: 1)With the increase of seismic peak intensity,the first area entered into plasticity transformed from the side wall on both sides to the spandrel and wall foot.2)The tunnel-soil system all occurred local instability first,and then the whole instability.3)Under the action of seismic shear wave,the response of circumferential fracture was smaller than that of longitudinal fracture.The spandrel and wall foot of lining structure were concentrated in tension or compression,which were the most unfavorable position of longitudinal crack.The failure mode of cracked lining tunnels was related to the buried depth condition and the stress state before the earthquake.4)The peak value of displacement time history curve was not a necessary and sufficient condition to determine the damage evolution of lining structure under the action of seismic shear wave,and the wave frequency of displacement should be considered at the same time.5)In the process of multi peak ground motion,the lining structure had accumulated damage,and the damage developed further in the process of ground motion re strengthening.6)The damage evaluation can reveal the damage mechanism,evolution process and failure mode of lining structure.The tunnel can often work with damage.Hence it is necessary to comprehensively evaluate the seismic safety of the cracked lining tunnel by combining the overall stability analysis of the tunnel-soil system.