| Xi ’an is located in the Fen-Wei seismic zone,which is a high-intensity fortified zone and surrounded by several fault zones.Under the background of urban expansion and continuous improvement of infrastructure,the construction of Xi ’an subway inevitably meets the special situation of intersecting with these fault zones,which brings new challenges to the seismic fortification of subway tunnels.In view of this,combined with the actual situation,this paper takes Xi ’an Metro Line 9 through the Mt.Li fault(which has multiple slip surfaces)as the prototype,and according to the similar three theorem,carries out shaking table tests on the shallow buried tunnel across the multi-slip surface fault in the loess region,and explores the response rules of the multi-slip surface fault site and shallow buried tunnel under the action of far-site seismic waves and near-site seismic waves.The main research contents and achievements are as follows:1.Based on the similarity theorem and dimensional analysis method,from the aspects of selection and treatment of test materials,model making process,model box treatment,observation point layout,loading scheme and so on,the shaking table test of shallow buried tunnel with excessive slip surface fault in loess area was designed and implemented.2.The seismic response rules of the multi-slip surface fault site are analyzed and summarized from the aspects of site damage,interaction of different parts of the site,surface settlement,site acceleration response,etc.(1)Under the action of longitudinal seismic load,the distance between footwall and fault is 330mm(0.66 times the fault width)and the distance between hanging wall and fault is630mm(1.26 times the fault width).The damage depth of the site is 450mm(0.9 times the fault width).(2)The interaction of soil mass in different sites is mainly caused by the displacements of different parts of soil mass out of sync and the different amplitude of displacement.The main fault interacts most strongly with the footwall field(3)The time-history curve of surface settlement displacement presents the feature of "inverted S",and the relative settlement displacement between the main fault and the soil on both sides is the largest.(4)Under the action of different seismic waves,the acceleration response of the site shows different laws.The acceleration response of the site is related to the damage degree of the site,and the acceleration response is more severe in the position where the damage degree of the site is large.3.The seismic response characteristics of shallow buried tunnel with excessive slip surface fault are analyzed and summarized from the aspects of macro-failure,acceleration response of footwall and strain response of tunnel.(1)In the multi-slip surface fault site with a width of 20 m,the most unfavorable position of the hanging wall tunnel is 290mm(1.23 times the hole diameter)away from the fault;The footwall tunnel has a most unfavorable range,that is,within 450mm(1.91 times the diameter of the hole)from the fault.(2)Based on the analysis of the change of the mechanical characteristics of the tunnel section,under the action of longitudinal seismic load,the influence range of the fault with a width of 20 m on the hanging wall tunnel is more than 3.19 times the cave Jing;The influence range of footwall tunnel is less than 3.19 times of cave Jing.The primary and secondary faults are the transition section of the tunnel section.(3)Under the action of different far-field seismic waves,the strain law of each tunnel measuring point is the same,and the strain peak value is roughly the same.The pulse wave is more destructive to the most unfavorable position of the tunnel.However,damage is not increased for tunnel structures outside the most unfavorable location.(4)Under the action of longitudinal seismic load,the circumferential tensile strain of the arches in the sub-fault section is large,especially the circumferential strain of the arches is close to the S2 section of the hanging wall(the section closest to the tunnel fracture)under the action of large earthquakes.(5)The hanging wall tunnel has obvious acceleration amplification effect.The acceleration amplification effect is related to the input seismic wave,and decreases gradually with the increase of the artificial wave peak in Xi ’an.With the increase of CHICHI peak value,the acceleration amplification effect increases gradually. |
