Shaking Table Model Tests And Numerical Simulation Study On Seismic Performance Of Single-pile Utility Tunnel

Known as “Lifeline Project”,the urban underground utility tunnels are important infrastructures to ensure regular operation of urban life,which contain water supply,drainage,gas,electrical facilities and other underground pipelines into the same underground space.Utility tunnels belong to underground shallow-buried structures and their seismic performance is significantly different from other underground structures such as subway stations.However,it will cause incalculable loss if utility tunnels are damaged in the earthquake,so it is essential to evaluate seismic behavior of utility tunnels.Based on methods of shaking table and numerical simulation,the objection of this thesis was to study the dynamic response of single-pipe utility tunnel under horizontal transverse uniform seismic excitation.Acceleration of tunnel structure and soil,soil seismic pressure,strain of tunnel and displacement of tunnel joint was emphatically discussed.According to results of numerical simulation,the factors affecting dynamic response of the utility tunnel was analyzed.The main conclusions of the thesis are as follow:(1)On the basis of a certain scale(1:15),shaking table model test of utility tunnel were carried out under uniform excitation in the transverse direction.The results showed that peak acceleration and acceleration amplification coefficient of soil decreased along depth when seismic intensity was low(PGA≤0.4g),while they decreased first and then increased along depth when seismic intensity was strong(PGA≥0.8g).The dominant frequency and corresponding amplitude showed the same distribution law.The acceleration amplification coefficient decreased with the increasing input accelerations.Acceleration response of tunnel with joint was generally weaker than that of joint-free tunnel when the input seismic signals were the same.(2)Acceleration response of side walls of tunnel structure was consistent with that of surrounding soil,which indicated that motion characteristic of tunnel was significantly influenced by surrounding soil under its constraint and they were sheared together.As PGA increased,the separation of soil and the structure possibly occurred where they contacted,while the tunnel structure kept a good integrity.(3)Along the direction of burial depth,the horizontal soil pressure was larger at upper and lower points and much smaller at middle points in the joint-free model test.The distribution curves of horizontal soil pressure along depth were approximately“W”-shaped indicating that the soil arching effect obviously existed.While the seismic soil pressure response became relatively smaller and showed insignificant variation along the depth in model test with joint.The distribution of vertical soil pressure was similar to that of horizontal soil pressure,but the value of it was much smaller.(4)By taking construction scheme of tunnel joints in practical engineering as a prototype and simulating their mechanical properties,a utility tunnel model with joint was carried out.The results indicated that rotation angles of the joint increased as PGA increased,while they were less than 0.5°respectively,thus the deformation at the joint could be ignored and would not lead to the failure of utility tunnel structure.(5)The seismic strain of structure was analyzed and seismic bending moment was calculated,it could be observed that the mechanical performance of tunnel structure was mainly affected by earthquake intensity.Moreover,seismic strain and seismic bending moment at corner points were much lager than at middle point,indicating that the connections between the roof(or the bottom slab)and the side walls was the key nodes to be considered in anti-seismic design.(6)Based on the UMAT subroutine in ABAQUS,the equivalent linear model of soil was developed.A plane strain model to study the dynamic behavior of utility tunnel was established.Results of numerical simulation showed that acceleration response of tunnel structure and soil were generally consistent with test results,and the seismic soil pressure of surrounding soil was distributed in jagged line under the influence of soil arching effect,while the soil arching effect was no longer obvious at a certain distance away from the tunnel structure.The peak main stress occurred at corner points as well.(7)The factors affecting the dynamic response of utility tunnel were discussed by numerical simulation method.The study found that strengthening the stiffness of soil around the tunnel structure and increasing the buried depth of tunnel could significantly weaken the seismic response of tunnel,thus the dynamic performance could be improved effectively.Nevertheless,it was not obvious to improve the dynamic performance of tunnel by increasing the concrete strength.