Study On Stress And Deformation Law Of Surrounding Rock Induced By Concealed Excavation Construction Of Metro Tunnel Through Ground Fissure Site

With the sustained and rapid development of China’s national economy and the further acceleration of urbanization,urban rail transit construction has made rapid progress,with an unprecedented scale of construction.However,the construction of urban rail transit is facing challenges from unfavorable geological conditions such as ground fissures,karst,fault zones,and special soils,which pose a significant safety threat to the construction of urban rail transit in China.Among them,the problem of ground settlement in the construction of metro tunnel in the ground fissure site is more prominent.Understanding the deformation law of surrounding rock in the construction of metro tunnel in the ground fissure site is an important prerequisite and foundation to ensure the construction of metro tunnel in the ground fissure site.Based on this,this article takes the CRD（cross diaphragm）construction method of the section tunnel of Xi’an Metro Line 6 as the engineering background,and uses physical model test to analyze the deformation and stress changes of surrounding rock during tunnel excavation and construction;A numerical model was established based on similarity ratio,and the deformation and stress changes of the surface and surrounding rock during tunnel excavation were calculated and analyzed,verifying the accuracy and reliability of the model test.At the same time,the influence of ground fissures on the deformation and stress field of surrounding rock under different angles of intersection between tunnels and ground fissures was analyzed.The main research findings are as follows:（1）Based on the physical model experiment with a geometric scale of 1:20,the variation characteristics of the surrounding rock displacement field and stress field of metro tunnel crossing the ground fissure zone by CRD construction method are studied.（2）Based on the physical model test,a numerical calculation model was established to simulate and reproduce the longitudinal and transverse settlement deformation process of the ground surface and tunnel vault caused by the excavation of metro tunnel under the orthogonal working conditions,as well as the stress change process of tunnel surrounding rock.The influence of ground fissures on the stress and displacement fields of surrounding rock during the excavation process was revealed,and the accuracy and reliability of the physical model were verified.（3）Based on the finite element numerical calculation software,taking the tunnel between Zhangba 4^th Road Station and Zhangba 1^st Road Station of Xi’an Metro Line 6Phase I Project crossing the f8 ground fissure zone as the engineering background,the excavation calculation models under different oblique conditions（60°and 30°）and different excavation directions（footwall to hanging wall）are constructed,and the strata The law of surface settlement deformation and the characteristics of stress deformation of tunnel surrounding rock.