Dynamic Response Analysis Of Tunnel In Liquefied Site

With the large-scale construction of the subway,some interval tunnels will inevitably approach or cross the liquefiable soil layer.In order to study the effect of foundation liquefaction on the dynamic response of subway tunnel,combined with actual engineering conditions,the liquefaction state of natural saturated sand foundation was analyzed by using FLAC3 D software firstly.Then,a soil-tunnel model was established and the dynamic characteristics of the tunnel structure and the liquefaction state of the surrounding soil were analyzed under conditions of uniform excitation,traveling wave excitation,different incidence angles of seismic wave and local liquefaction.Finally,the post-earthquake settlement of the tunnel was analyzed.Main conclusions are as follows:(1)Under earthquake,the liquefaction range of natural saturated sand foundation is mainly within 16 m below the surface.(2)In the process of uniform excitation,the liquefaction state of the surrounding soil will be changed due to the existence of lining structure.Because of the site liquefaction,the tension part is inclined to the arch waist,and the compression part is inclined to the invert arch.Under the excitation of traveling waves,the lining response is out of sync along the axial direction.The D-value of lateral displacement between the lining ends is larger,and the lining bears torque.Under the excitation of different wave speeds,the dynamic response of lining is mainly reflected in the lateral displacement.With the increase of wave velocity,the lateral displacement response of lining decreases gradually.(3)When the subway tunnel passes through the partially liquefiable soil,the displacement and the stress of lining in different soil layers are quite different.Especially at the boundary of the soil layer,there are obvious changes in the main stress.The failure zone of the lining is extended to all parts of the lining section,and the structure is easily destroyed.(4)Under the excitation of different incident angles of seismic waves,the degree of liquefaction of the soil around the lining is basically the same.With the increase of the incident angle,the lateral and vertical displacement of the lining will decrease,and the radial stress will increase firstly and then will decrease.The circumferential stress will decrease gradually,and the longitudinal stress will increase gradually.