Study On Effect Of Overlaying Soil Rupture Induced By Dislocation Of Active Fault On Metro Tunnel

In China,active fault is widely distributed especially in the central and western regions.With the implementation of China’s "the Belt and Road" national strategy and the acceleration of urbanization process,high speed railway,highway and urban rail transits will inevitably pass through or close to the fault zone.So the existence and development of the fault zone will bring serious threat to the large-scale construction projects.Once the rupture slip or earthquake occurred,it will cause a major impact on the overlying soil layer and the structure of the tunnel.Therefore,based on the background of Xi’an metro line passing through the active fault,the study on the response of overlying soil due to bedrock dislocation of earthquake fault and its effects on metro tunnel was carried out by numerical simulation and theoretical analysis.In this paper,the influence of main various factors on the rupture and expansion of overlying soil is mainly analyzed,to reveal the inherent law of deformation and rupture of overlying soil.In addition,the response characteristics of subway tunnel under the fault slip and earthquake are studied respectively.Finally,the prevention and control measures were proposed.The main work and research results are summarized as follows:(1)The characteristics of the Lin Tong metro line crossing the active fault zone was fund out and the seismic tectonic characteristics of the site were evaluated,and the maximum vertical displacements of active fault was estimated.(2)The influence of thickness of overlaying soil,bedrock dislocation angle,fault dislocation and soil mechanics parameters on deformation of fracture of overlaying soil was analyzed by two-dimensional finite element geological model.And the deformation characteristics of overlying soil,stress state of soil and critical dislocation were revealed respectively.And the rupture process and mechanics mechanism of the overlying soil under active fault were summarized.(3)The three-dimensional finite element model of metro tunnel-active fault-stratum was built based on finite element theory.Through the numerical simulation,the changing characteristics of tunnel settlement deformation,stratum stress and structural internal force were analysised.Influence scope of both sides of avtive fault were given,the characteristics of structure force are discussed,effect mechanism of metro tunnel under the movement of active fault were summarized.(4)Three-dimensional dynamic model of metro tunnel-stratum-fault was established by finite difference theory.The response characteristics of metro tunnel under the influence of earthquake action were analyzed.The dynamic response rules were revealed of metro tunnel under earthquake power including the acceleration,displacement,soil pressure and structure internal force.The results showed obvious hanging wall effect on response characteristics of tunnel structure.Influence scope of metro tunnel crossing the avtive fault under the earthquake action were given finally.(5)Based on the influence scope of metro tunnel under the dislocation of bedrock fault and earthquake action,the theoretical fortification value of metro tunnel passing through active fault was proposed.Considering the safety of engineering and complexity of avtive fault,the recommended value of fortification value was given-namely 75 m in the hanging wall and 50 m in the footwall.From the perspective of engineering design and construction,the prevention and control measures of tunnel passing through the active faults were proposed.