Field Test Of Subgrade-Tunnel Transition Section Of Ballastless Track On Suining-Chongqing Railway And Subgrade Structure FEM Calculation

China railway construction is at a high development stage, and because the ballastless track can obviously reduce maintenance workload and increase the safety and comfort of the high-speed train, the ballastless track structure laid on soil subgrade in the high-speed railway has become an inevitable trend. At present, the ballastless track has been largely laid on Suining-Chongqing ballastless track railway, Beijing-Tianjin inter-city railway, Wuhan-Guangzhou express railway, Zhengzhou-Xi'an express railway, Haerbin-Dalian express railway and Beijing-Shanghai high speed railway.In order to adapt changes in topography of the ups and downs, there will be a large number of tunnels, bridges and other structures along rail line. As the subgrade and tunnel are under the different supporting conditions, the stiffness and deformation of foundation under rail track and even the whole track structure will be different, which will cause the significant irregularity phenomenon in subgrade-tunnel connection yield. The additional dynamic power will increase noticeably when the train passes through this part, which will take a negative impact on the traffic security and comfort. In order to reduce the track stiffness and deformation mutation caused by additional dynamic power, it is a technical treatment measure to set up a certain length of the transition between the subgrade and tunnel.Integrating the comprehensive vehicle test on Suining-Chongqing ballastless track Railway and simulation research on twin-block ballastless track structure, the paper studied and analyzed the subgrade dynamic stress, the supporting vibration displacement and vibration velocity magnitude, their relationships with the speed of trains, and the rules in the direction of the railway line of the concrete transition between subgrade and tunnel under the load role of CRH2 multiple units and C80 heavy haul freight trains. At the same time, it started FEM calculation of the twin-block ballastless track structure and analyzed the twin-block ballastless track key structure mechanical response under conditions of different axle loads, structure contact, supporting modulus, surface layer of subgrade modulus and discount rate of rail track modulus. The test data showed that the subgrade dynamic stress, the supporting vibration displacement and vibration velocity of the ballastless track were relatively smaller than that of the ballasted track; the axle loads took a significant role to the subgrade dynamic stress, the supporting vibration displacement; the train speed and vehicle dynamic performance had a great impact on the supporting vibration velocity; the dynamic stress, vibration displacement and vibration velocity changed stably in the direction of the railway line; the aim was basically achieved that the supporting rigidity transited gradually between the subgrade-tunnel transition. The FEM data showed that the axle loads distribution extent of subgrade surface close to 5 m; the ballastless track subgrade structure mechanical response increased by the increasing axle loads and the decreasing supporting modulus;in the paper's assemble modulus,0.66 discount rate is a good rail track modulus; the subgrade mechanical properties of the structure layers under the conditions of coupling were closed to the of vehicle test data ,but the subgrade mechanical properties became more poor when the frictional contact increased.Through the comparison of vehicle test results and FEM simulation results, it can be established that this model can better simulate the subgrade mechanical respones of twin-block ballastless track structure on soil subgrade.