Study On The Mechanism Of Mud-Pumping Of High-Speed Railway Subgrade And Its Caused Wheel-Rail Dynamic Responses

Due to the complicated geological conditions in China,the situation of mud-pumping in Chinese railway subgrade is very serious.With the rapid construction and operation of high-speed railways in China,mud-pumping has also begun to occur on ballastless tracks frequently.At present,domestic and foreign theoretical and experimental researches on mud-pumping are mainly in ballast tracks,but the research of the mechanism of mud-pumping in ballastless tracks is rather little.Based on two methods of physical model test and numerical simulation,this paper systematically studied the mechanism of high-speed railway mud-pumping and the deformation and mechanical characterization of CRTS I ballastless tracks and the dynamic responses of trains,which is resulted in the uneven subgrade settlement caused by subgrade degradation.The main research work carried out in this paper and the corresponding research results are as follows:(1)By analyzing the turbidity collected from each layer,when the hydraulic gradient reaches a certain level at the interface of the double-layer,the fine particles in the sandy soils will continue to flow to the graded gravel layer.After the fine particles in the sandy soils flow to the fourth layer of graded gravel,the waterhead in the internal of graded gravel fluctuates with the loading curve,which has a "pumping"effect on the fine particles,so the fine particles are exchanged inside graded gravel.Finally,the fine particles reach the surface of graded gravel,which will eventually lead to the occurrence of mud-pumping;(2)According to the hysteresis loop curves of graded gravel,it is obtained that the resilient modulus of graded gravel attenuates with the increase of load amplitude,and the damping ratio increases with the increase of load amplitude;according to the data obtained by LVDT and magnetoresistive magentomenter,the permanent strain and elastic strain of graded gravel under two different moisture contents increase with the increase of stress amplitude.The plastic strain and elastic strain of graded gravel under saturated moisture content are greater than that of graded gravel under optimum moisture content;and the theoretical permanent deformation of graded gravel under staged loading is proposed;(3)Water is easily accumulated in the expansion joints of CRTS I slab tracks,which causes uneven moisture content of the subgrade under slab tracks.Subgrade with high moisture content is prone to large permanent deformations.After years of operation,uneven settlement will occur on the surface of subgrade under CRTS I slab tracks.Based on the above phenomena,a three-dimensional finite element model of train-CRTS I slab ballastless track-subgrade was established,which is applied to uneven settlement,and the feasibility of the numerical model was verified;(4)After the occurrence of subgrade uneven settlement,whether the end of the track structure can contact the subgrade is affected by the wavelength,amplitude and dynamic loading;under the train dynamic loading,the compressive stress on the surface of subgrade can even reach 1 MPa,and only the uneven settlement corresponding to the wavelengths of 2 m and 4 m can meet the fatigue strength of concrete;summarize the service performance standards of domestic and overseas and the service performance standards of German and Japanese high-speed railways are laxer than those of Chinese;for train running performance,according to the design specifications of Chinese high-speed railway,the conditions of 6 m/100 mm,8 m/10 mm,and 10 m/10～15 mm,15 m/20～30 mm,20 m/25～40 mm will cause track degradation,and the safety of trains is threatened under the conditions of 6 m/15～40 mm,8 m/15～40 mm,10 m/20～40 mm and 15 m/35～40 mm.