Research On The Cwr Stability Of High Roadbed Section In Permafrost Regions

In order to improve the national railway network construction, speed up economic development of the western region, the Qinghai Tibet railway, which is the first representative railway in plateau region, has done some reform on the existing line, at the same time, expanded the mileage construction. Because of the special climate in the plateau region, added the great changes of daily and year temperature difference, the soil condition along the Qinghai Tibet railway is more complex than the general area, and the large distribution of permafrost area make the plateau railway construction and maintenance and repair more difficult. Laying CWR can not only improve the comfort of passengers and the train operation speed, but have the obvious advantages than ordinary lines in line maintenance and repair, operation cost and transportation efficiency, etc. As a result of what, CWR has been applied in the railway construction in western plateau region.It has got some achievements of laying CWR in un-always permafrost region, the operation behaves well, but to the always permafrost area, many ultra-high roadbed sections have been found in the Qinghai Tibet railway permafrost area during the site investigation process. Combined with the maintenance and site observation, there are two reasons that leading to the ultra-high roadbed: on the one hand, when carry out the maintenance and repair work, due to the lack of special large maintenance machinery for the plateau region, the only way to complete the machine maintenance is by raising the roadbed, which leads to the increasing of the roadbed thickness. On the other hand, because of the instability of the subgrade soil in permafrost region, the freeze-thaw cycles of soil lead to uneven settlement on both sides of subgrade, against this line disease, it is by adding ballast to meet the requirements, which will lead to the further increasing of the roadbed thickness.The gap between the new ballast, which will get mutual integrated and compacting under the effect of vehicle load, will also cause the uneven settlement, leading to the irregularity of rail surface. The excessive elevation of roadbed makes the original subgrade structure not meet the requirements of line bearing capacity and stability. As a result, from deformation of the roadbed under repeated loading and the observation data of subgrade deformation, research the mechanism, analyze the formation reasons, and find out the corresponding countermeasures, which are very necessary.The paper mainly researched the following four aspects:1) According to the deformation principle of subgrade in the permafrost region and the related factors affecting the subgrade deformation, analyze the track settlement caused by subgrade subsidence, through the calculation method of equal volume and the related principle of subgrade deformation. Establish ANSYS model of the composite element test(CET) referring to the relevant calculation models, and get the settlement rules of roadbed under repeated loads after simulation analysis, finally get the trend graph about the changing of roadbed thickness in permafrost region.2) Against the ultra-high roadbed in permafrost region, it is inevitably that the shoulder width will be insufficient and the ballast wall may get severe deformation, which will cause the subsidence of roadbed and have some impacts on the stability of laying CWR. Especially the reduce of ballast lateral and longitudinal resistance will influence the laying range of CWR. Therefore, it should design different improving programs from general subgrade and subgrade front of bridge.3) Design the structure of the CWR in high roadbed section in permafrost region that is reinforced, which include the design and the calculation of rail strength and track stability, determine of the stress-free rail temperature, and the calculation of rail gap. Based on the Qinghai Tibet railway project, quantitatively analyze the influence of the ballast lateral resistance reducing to the line stability. Combined with the calculation method of hanging sleepers caused by non-uniform roadbed subsidence, get the uneven settlement value of subgrade under the condition of critical to hanging sleeper, and take which as the technical index of CWR subgrade deformation in permafrost region, to make judgement on the suitability of laying CWR in permafrost region.4) CWR in Qinghai Tibet railway permafrost region, influenced by the special alpine climate, there must be temperature stress internal the rail during the operation, which will seriously affect the line stability and the operation safety. So it must carry out the maintenance and repair work based on the line situation when CWR in permafrost region get into operation. The paper researched from the setting of displacement observation piles, release of the stress internal the CWR rail, and the maintenance system, put forward some daily maintenance and repair measures of CWR in permafrost region.