Research On Law Of Ballastless Track Rail Heave By Subgrade Or Foundation Swelling Of High Speed Railway

Double-block ballastless track is the most advanced track technology at present,which is widely used in high-speed railway construction.It has strong stiffness and strength,but weak adaptability to substructure deformation,especially for subgrade swelling deformation,weak subgrade swelling may induce obvious rail arch.There are two fundamental reasons for the expansion of high-speed railway subgrade: the use of subgrade filler with slight swelling or the line running in the swelling stratum.A large number of high-speed railway construction engineering practices show that the existing standards for the swelling of the filling and foundation of ballastless track have been difficult to meet the high precision requirements of ballastless track.Field monitoring(longitudinal continuous deformation monitoring and stratified deformation monitoring combined with the detection data of the moving vehicle in the early stage),laboratory test(basic geotechnical test and swelling mechanism test)and DEM-FDM coupling numerical simulation methods are adopted to study the rail arch disease induced by the expansion of ballastless track subgrade of high-speed railway.The arch displacement distribution characteristics and axial stress development law of ballastless track caused by different expansion conditions of subgrade model are discussed.Based on the systematic analysis of the rail arch disease on site and the laboratory test,the expansion mechanism of the subgrade filling and foundation mudstone at the construction site of the rail arch is discussed,and the following conclusions are finally drawn.(For various reasons,all the pile numbers and section information in this paper have been processed to some extent).1.Based on the field monitoring of two study areas of a passenger dedicated line in the west of China,it is found that the peak values of rail arch in the study section have been developing continuously,and the peak values of rail arch in the two study sections are 11.47 mm and 16.74 mm respectively.The peak value of the upper arch is close to the abutments on both sides of the water-over structures,and the distribution range of the upper arch in the two study sections reaches 20m-51 m and 63 m respectively.2.Through stratified monitoring,it is found that the subgrade swelling is mainly in the foundation,but there is also a small amount of swelling deformation in the filling part of the subgrade.It is considered that the upper arch of the rail is caused by the swelling deformation of both the filling part of the subgrade and the mudstone of the foundation.The maximum deformation of foundation in the transition section of K1000+300 ～ K1000+700 road and bridge reaches 10.15 mm.The maximum deformation of foundation in transition section of culvert K1004+276 ～ K1004+316 is up to 10.16 mm,and the cumulative deformation of filling part is up to 4.68 mm.3.Swelling tests were carried out on the subgrade filler and mudstone samples obtained from the field.The results show that the final swelling rate of the filler is positively correlated with the content of montmorillonite,and negatively correlated with the voidage.Based on the analysis of the double-factor test data,a parameter β is put forward to evaluate the swelling property of high speed railway subgrade.The parameter β is positively correlated with the swelling property of subgrade material.4.According to the void fraction-montmorillonite content two-factor experimental analysis think packing swelling mechanism of the whole show as follows: when packing in the swelling volume increment which caused by the mineral in after filling the void volume packing itself continue to swell,causes the aggregate particles from swelling in the filler particles lifting effect finally show the overall sample size.5.The results of water-controlled swelling tests on subgrade filler and foundation mudstone show that the swelling rate of foundation soil is 2.656% under the condition of in-situ moisture content,and that of subgrade filler is 0.027%.After fitting the relationship between the swelling rate and water content of the two materials,the expression between the swelling rate and water content of the subgrade filler and the foundation mudstone was obtained.With the increase of water content,the swelling rate of the subgrade filler finally converged to 0.49%,while the swelling rate of the mudstone finally converged to 6.398%.6.The numerical simulation results of the arch on the rail of ballastless track induced by the swelling deformation of subgrade filler and foundation mudstone by DEM-FDM coupling numerical simulation method show that the peak value of the arch on the rail and the swelling rate of subgrade filler and foundation soil follow the linear relationship from EXPASSOC and respectively.When the moisture content of the subgrade filler is 12.424%,the swelling rate of the subgrade filler reaches 0.262%,and the induced arching amount on the rail reaches 1mm.However,when the moisture content is 3.712%,the swelling rate of the foundation mudstone at the site is 0.768%,and the induced arching amount on the rail is the adjustable critical value of 4mm.7.From one side of the swelling zone to the other side,the axial stress of the rail head can be roughly divided into compressive stress zone,tensile stress zone and compressive stress zone.The stress difference between the axial tensile stress peak of the rail in the center of the upper arch zone and the compressive stress peak at the arch foot has a positive correlation with the swelling rate of the base bed filler and mudstone foundation soil.