Study On Transfer Behavior Of Embankment Foundation Differential Settlement And Bridge/Approach Location Dynamic Experiment Of High-Speed Railway Ballastless Track

Most of high-speed railway embankments are constructed with high quality filler and high compaction degree. The embankment is constructed according to the design technical specifications of high speed railway and in the normal state, its settlement is mainly induced by the foundation in the process of long time useage.The foundation usually has a large difference settlement in the position of the foundation soil layers with great changes and the joint with defferent foundation treatment.Especially the uneven deformation of subgrade surface will generated on the bridge/approach location and further caused serious track irregularity. There are differences of deformation form and the degree of uneven deformation between the subgrade surface and foundation surface, under the action of transfer diffusion of the embankment.CRTS II slab ballastless track was put to use in the Beijing-Shanghai highspeed railway.In order to restrain displacement of longitudinal connected slab ballastless track on the bridge caused by temperature change,the60m long anchorage system which is made of friction slab interim plate and end thorns structure et al was built on the subgrade of the bridge/approach location.The existence of the end thorns structure changes the traditional bridge/approach location basic form of flexible embankment directly connected to the rigid abutment.Developing the vibration characteristics test on CRTS II slab ballastless track bridge/approach location and mastering the vibration response of spatial change characteristics along the road longitudinal and vertical direction and the relationship between the speed of train and the vibration response have significant to improve continuity between the both ends of end thorns structure and the road and bridge structure connected position.Then refer to the research on this area both inside and outside,the experimental study were developed about the transfer behavior of high-speed railway embankment foundation differential settlement and the dynamic performance on CRTS Ⅱ slab ballastless track bridge/approach location.This paper has done some research on the following aspects.1. Transfer Behavior of Differential Settlement of Embankment Foundation Based on Centrifugal Model TestsTo study the embankment foundation differential settlement transfer behavior in the embankment and the influence mechanism on the uneven deformation of subgrade surface, firstly differential settlement of embankment foundation is respectively simplified as two kinds of models(stagger-step model and gradual change model). Through a set of own-designed and manufactured precise control equipment, which can real-time control foundation differential settlement in centrifuge operational state, carry out6centrifuge model tests, etc,the embankment height of3m,6m,9m, and foundation gradient segment length of4m,8m,12m. Focus on measuring distribution of uneven deformation along the road longitudinally, caused by the differential settlement of foundation subgrade surface. Analysis the affection to the uneven deformation of subgrade surface, including differential settlement size of embankment foundation, height of embankment, the length of gradual section of differential settlement. Test study show as follows:Uneven deformation of subgrade surface which caused by differential settlement shows "S" distribution Characteristics; the relationship between angular of uneven deformation on subgrade surface and amplitude of differential settlement in foundation is generally a linear. When there are the same angular of uneven deformation on subgrade surface, high embankment or set the gradual section on the bottom of the embankment will increase the allowed values of differential settlement on foundation. Based on the limited angular values of uneven deformation on subgrade surface, put forward the control limit of differential settlement on foundation, considering height of overlain embankment and the gradual section set on the bottom of the embankment foundation. It means a lot to the parameter system of settlement deformation control about railway subgrade.2. Long-term Field Test and Settlement Assessment Analysis of Bridge/approcah LocationCombined with the construction of the Beijing-Shanghai high-speed railway and based on sensor-networks automatic test system, long-term field tests were developed at bridge/approach location of Gaozi’east grand bridge at Beijing direction and Tianjin grand bridge at Shanghai direction. In order to conduct a statistical analysis of settlement deformation data from the abutment and adjacent subgrade,77representative bridge/approach location were selected from the settlement assessment data of Beijing-Shanghai high-speed railway JHTJ-5tenders. Test study show as follows:The settlement deformation of embankment foundation and subgrade surface at bridge/approach location are so smaller that they are all in a stable state and meet the design and control requirements, measures of foundation treatment and embankment filling have played a significant effect.The vertical differential settlement between embankment and the abutment is gradually increasing over time and tends to be stable.Extended roadbed placed time helps to reduce the differential settlement of bridge/approach location.The water content of embankment has a cyclical changed phenomenon that it is high in summer while low in winter. Season change has great influence on subgrade surface water content, with the increase of depth it tend to be stable.the height of the abutment and the depth of pile under abutment have small influence on bridge abutment settlement. With the increasing of embankment height and foundation reinforcement depth, foundation deformation at bridge/approach location tends to be a slight increase.Settlement at bridge/approach location along longitudinal from abutment to embankment is gradually increasing,The longitudinal slope of subgrade is changed at0.03‰-0.44‰, which is less than l‰the required value of deflection angle at bridge/approach location.3. Test and Analysis of Vibration Characteristics on CRTS Ⅱ Slab BallastlessTrack Bridge/approach LocationCombined with comprehensive test of the pilot section of the Beijing-Shanghai high-speed railway, the test of the vibration characteristics of the bridge/approach location under the conditions of high-speed operation of93trips has been carried out in the Sui River bridge abutment to shanghai derection. The maximum speed reached up to424km/h and dynamic response has been obtained. The vibration response of the vibration displacement, vibration velocity, vibration acceleration on the structure key parts of the both ends of the end thorns structure which adjacent to the road and bridge structure connected position were developed, and the relationship between the speed of train and the vibration response are analyzed.Test study show as follows:Along the road longitudinal direction the maximum value of vibration response is located at the junction of the end thorns structure transition board side and the subgrade bearing layer,showing that the support stiffness of the former is less than the latter; On the vertical multi-storey structure layers the vibration response is relatively large when the horizontal direction structure is discontinuity and show a decreasing trend along the depth,but the vibration characteristics is significantly improved when the track slabs are longitudinal connected; With the train speed increased the vibration displacement show a linear increase while the vibration velocity and vibration acceleration show a nonlinear accelerated increase relationship.4. Double Elastic Foundation Model Analysis Method of Ballastless Track Subgrade Mechanical Response Under Vehicle Load To study the load characteristics of the vehicle axle load through ballastless track system to the subgrade structure, The Winkler spring foundation infinite beam model and Boussinesq solution of Hooke elastic foundation are employed. Using the iterative algorithm and foundation coefficient as control condition,the stress response analysis method of double block ballastless track with vehicle axle loads is built through the use of Winkler spring foundation and Hooke elastic foundation (double elastic foundation model analysis method).Computational analysis shows that vehicle axle load has significant effects on subgrade structural stress and deformation and with the increase of axle load subgrade structural stress and deformation increase linearly.Track stiffness has a significantly influence to the subgrade surface stress and deformation. With the attenuation of track stiffness, the subgrade surface stress and deformation will increase, particularly the extreme cases when the track plate and the supporting layer fracture.Increasing the width of the supporting layer can significantly improve the force and deformation of subgrade surface, but increasing the roadbed slab width is ineffective. Changes in the formation surface thickness of the subgrade surface less impact the force and deformation. The reduction of the modulus of the foundation bed will significantly reduce the ground coefficient.