Study On Dynamic Response Of Subgrade Of High-speed Railway Crossing Ground Fissure Site

High speed railway is an important part of China’s transportation system and the main artery of national economy,which plays a vital role in China’s social and economic development.In the context of vigorously advancing the "One Belt,One Road" national strategy,high-speed rail has entered a new stage of rapid construction.However,China’s vast territory,high-speed railway construction is facing the challenges of ground fissures,karst,collapsible loess and soft soil and other adverse geological conditions,of which a considerable number of high-speed railways have been built,under construction and planned to pass through the ground fissures,which brings serious security risks to the construction and normal operation of high-speed railway! Therefore,it is not only of great theoretical significance,but also of great practical value to study the dynamic response mechanism of high-speed railway subgrade and foundation under train vibration load.In this paper,taking the Daxi passenger dedicated line as the research project background,the subgrade section of high-speed railway passing through the ground fissure site of Dongguan substation in Taiyuan Basin of Shanxi Province is selected as the research object,and the large-scale physical model test of embankment—ground fissure —natural foundation interaction under the high-speed train vibration load is designed and carried out.Combined with the finite element dynamic numerical simulation calculation,the effect of train vibration load is analyzed in this paper,the dynamic response mechanism of high-speed railway subgrade crossing ground fissures is studied.The research results can provide scientific basis for the design and disease prevention of high-speed railway subgrade crossing ground fissures.The main research results are as follows:(1)A high-speed railway train vibration load excitation system suitable for large-scale physical model test is developed.The system includes vibration exciter,traction power equipment,safety device and control system to simulate high-speed railway load.The effective simulation of high-speed railway train vibration load in large-scale physical model test is realized.(2)The dynamic response characteristics of the model system are studied,and the dynamic response law of the hanging wall,footwall subgrade and foundation of the ground fissure site and the attenuation law of the dynamic response along the depth direction of the ground fissure site are revealed,It is found that the amplitude of dynamic acceleration increases in the hanging wall near the ground fissure and decreases in the footwall under the action of train load.The peak frequency of the measuring points near the ground fissure is about 40 Hz,and the peak frequency of the measuring points far away from the ground fissure is between 20-30 hz.(3)A three-dimensional dynamic finite element model of ground fissure zone-double track subgrade-foundation(natural foundation and CFG pile composite foundation)is established.The dynamic responses of natural foundation and high-speed railway subgrade on composite foundation under the condition of single track and double track operation of train are compared and analyzed,and the dynamic response law of double track high-speed railway subgrade in ground fissure site is revealed,It is found that the amplitude of subgrade dynamic acceleration jumps on both sides of the ground fissure along the longitudinal direction while the subgrade dynamic acceleration fluctuates along the longitudinal direction.At the same time,the CFG pile raft composite foundation can significantly reduce the dynamic response of each layer of the embankment under the single track operation and double track operation,and can eliminate the dislocation near the ground fissure during the single track operation;The dynamic displacement and stress of the hanging and foot walls of the ground fissure satisfy the first-order function relationship with the driving speed,while the dynamic acceleration and driving speed satisfy the second-order function relationship.