Numerical Simulation On Dynamic Response Of High-speed Railway Subgrade Crossing The Ground Fissure Zone

Railway transportation is the main artery of national economy and plays a very important role in China’s economic and social development.Especially in recent years,the construction of high-speed railway has played a great role in promoting the rapid development of China’s social and economic development.However,due to the complex geological conditions in China,large-scale high-speed railway construction is faced with geological disasters and special geological challenges such as land subsidence,ground fissure,karst and soft soil,collapsible loess and so on,among which the ground fissure are relatively prominent.The influence of active ground fissure on high-speed railway and the dynamic response of subgrade across ground fissure zone under the action of vibration load of high-speed train are important issues that must be considered when high-speed railway passes through the active ground fissure zones.Up to now,the research on dynamic response of subgrade under train vibration load is almost blank.Therefore,it is of great theoretical and practical significance to study the dynamic response mechanism of high-speed railway subgrade across ground cracks under the action of train load.Based on the national natural science foundation project "dynamic response mechanism and long-term settlement study of subgrade of high speed railway across ground crack zone(41772274)",this paper takes the Datong-Xi’an passenger dedicated line crossing ground fissure zones as the research background,and with finite element numerical method the foundation-ground fissure-embankment dynamic calculation model under the action of high-speed train load was established.The dynamic response characteristics of subgrade crossing the ground fissure zone with orthogonal and oblique crossing are studied.It analyzes the influence law of subgrade parameters(elastic modulus of the basement bed,elastic modulus of embankment body,thickness of concrete and length of pile)on dynamic response of subgrade in ground fissure zone.Based on the orthogonal test method,the optimization combination of design parameters of the subgrade of CFG pile composite foundation with ground fissure zone was determined.Therefore,the research results of this paper are as follows:(1)Based on the dynamic finite element method,the three dimension calculation model of foundation-ground fissure-embankment was established.The dynamic response characteristics of high-speed railway subgrade with natural foundation and composite foundation crossing the ground fissure zone were studied,including dynamic displacement,acceleration and dynamic stress response rules,and dynamic response characteristics of the concrete and CFG pile in composite foundation.It analyzed the influence of train speed on dynamic response of subgrade.It reveals the influence law of ground fissure on dynamic response of high-speed railway,and determines the influence range of ground fissure.(2)Based on the finite element calculation model of embankment-ground fissure-foundation,the dynamic response characteristics of subgrade obliquely across the ground fissure zone of high-speed railway are analyzed,including dynamic displacement,acceleration and dynamic stress response rules,and the influence law of the change of intersection Angle between high-speed railway and ground fissure on the dynamic response of subgrade is revealed.(3)The interaction of ground fissure,embankment and foundation is considered with three-dimensional finite element numerical simulation,to analyze the influence of subgrade parameters including the elastic modulus of the basement bed,the elastic modulus of embankment body,the thickness of concrete and the length of pile on the dynamic characteristics of subgrade in ground fissure zone.Based on the orthogonal test design,it analyzes the influence of each factor level change on the test index,and obtains key influencing factors and optimal parameter combination.The optimal design scheme for the subgrade parameters of CFG pile composite foundation in ground fissure zone is 120 MPa for the basement bed modulus,60 MPa for the embankment body modulus,1.4m for the concrete slab thickness,and 20 m for the pile length.