Key Issues Of Laying CWR Design In Qinghai-Tibet Railway

With the improvement of road network in western China, the mileage of Qinghai-TibetRailway and Lhasa-Shigatse railway are increasing. Railway in plateau region is characterizedby harsh natural conditions, complex project conditions, low average annual temperature,large diurnal temperature range, wide distribution of the perennial permafrost region, etc.Laying CWR can effectively improve passengers’ comfort and vehicle’s speed, reduce theworkload of track maintenance and the line operation costs, and improve the transportefficiency. In recent years, it has gradually been applied in the Qinghai-Tibet Railway.In order to enhance the transport capacity, comfort and stability of lines, reduce trackmaintenance and repair, it was from2011that began the CWR transformation ofGeermu-Lhasa segment, based on laying CWR in Xining–Geermu segment and thepermafrost region of Geermu-Lhasa segment., Qinghai-Tibet Railway is from Geermu inQinghai, west to Lhasa in Tibet, whose total length is1,142km, of which, there are960kmrailway4000m above sea level, and550km railway in permafrost region. The extremeweather conditions and a broad distribution of permafrost region have put forward higherrequirements of laying CWR in Geermu-Lhasa segment. It is quite important of improving theCWR design level of the Qinghai-Tibet Railway, and ensuring the traffic safety, to researchthe key issues of laying CWR design in alpine region from the design of stress-free railtemperature, selection of the CWR structure, design of the special bridge structure, and thetreatment of ultra-high roadbed in subgrade,The paper carried out the research mainly from the following aspects:1) The determine of stress-free temperature should consider the allowable temperaturerise and the allowable temperature drop, to prevent track buckling at high temperature andbreaking at low temperature. The annual temperature and diurnal temperature inGeermu-Lhasa segment of Qinghai-Tibet Railway are higher than that in the ordinary segment,the internal temperature in long rail change with a high frequency and large amplitude.Combined with rail temperature and line conditions data of the Geermu-Lhasa segment, thepaper researched the determining method of the allowable temperature rise rang and theallowable temperature drop range, determined the reasonable stress-free rail temperature andselected appropriate track structure, and researched the feasibility of laying seamless turnoutin Qinghai-Tibet railway, focused on the convergence transition of P50and P60turnout.2) Because of its unique geology, environmental characteristics, there are a lot ofcharacteristic bridges with numerous structure types in Qinghai-Tibet railway. CWR on bridgeis influenced by the additional stretching force and bending force, which need to beindividually designed in high altitude region. Combined with the specific projects of layingCWR on Lhasa–River super-large bridge in Qinghai-Tibet railway, the paper researched theselection problems of CWR design schemes. Proposed the solutions that how to expand CWR on bridge, from improving the allowable temperature rise range and the allowable temperaturedrop range, reasonably determining the stress-free rail temperature and its allowable range.In addition, because of the increase of rack bed thickness, the heightening of ballastretaining board should be considered during the CWR design on bridge. The paper designedtwo types of ballast retaining board of35cm and45cm, and inspected and calculated itsstability.3) Considered the increase of bed thickness caused by the maintenance and the subgradesettlement, the paper used finite element method to analyze influence of bed thicknessvariation to CWR stability. Designed schemes of using soil subgrade and dry rubble pile towiden the shoulder width, which are used in the actual project4) During the laying and maintenance process of CWR in Qinghai-Tibet railway, thestress-free temperature may get changed and beyond the design range for the influence ofsubgrade thaw settlement, frost heaving and the heightening of track bed. Therefore, it isimportant to analyze the displacement observation and the actual stress-free rail temperaturecalculation method of CWR in the alpine region, strengthen the rail temperature monitoring,adjust the stress relief if necessary, and in special sections, it can be designed to the regularstress relief CWR, to ensure the safe operation of line.The paper have researched on the determine of stress-free rail temperature, structureselection of CWR on bridge, influence of ultra-high bed, selection of shoulder widen methodsand long rail stress relief methods in alpine region, which have been applied in practice inlaying CWR in Qinghai-Tibet railway, and got good effect.