Research On Stress Analysis & Design Method Of Heavy-haul Railway Subgrade Bed

The stress analysis of the heavy-haul railway subgrade bed in China mainly adopts the Boussinesq theoretical calculation method.This method has insufficient research on the load sharing coefficient and this method does not systematically summarize the difference in stress distribution in the subgrade under the action of 25 t axle weight ~40t axle weight.China’s " Design Code for Heavy-Haul Railways" has adopted the strength control criteria to establish relevant standards for heavy-haul subgrade bed structures,but there is still room for optimization and expansion.By studying the stress analysis and design method of heavy-haul railway subgrade bed,the stress distribution in the subgrade is systematically summarized,and the optimization suggestions for the structural design method of heavy-haul railway subgrade bed are put forward,which is of great significance for improving the structural design level of heavy-haul railway subgrade bed in China.By means of domestic and foreign data investigation,laboratory test,scale model test,finite element numerical calculation analysis and theoretical analysis,the influence of different parameters on the distribution law of subgrade internal stress was studied.The main research results are as follows:1、China’s " Design Code for Heavy-Haul Railways " subgrade bed design standards are stricter than other countries.The United States,Australia,South Africa and other countries have their own mature standard system,most of them adopt the strength control standard design,generally strengthen the surface layer of subgrade,filling type provisions are basically the same,compaction degree aspect of China’s specification requirements are more stringent,more inspection indicators,but the foreign requirements for CBR than China’s strict.2、The relationship between the distribution of subgrade stress and vehicle parameters,track structure parameters and subgrade bed parameters is systematically summarized.The difference between the finite element simulation calculation and the Odemark equivalent theory and the Boussinesq theory is less than 5%,which basically conforms to the measured dimensionless stress decay curve;Vehicle axle load and other parameters have a great impact on the internal stress of the subgrade bed.The difference between the subgrade stress of 25 tons axle load and 40 tons axle load is 43.9kpa,and the increase is basically linear.The state change of the track structure has a great influence on the stress distribution in the subgrade bed.Under the condition of 40 t axle weight,the stress amplitude of the subgrade surface can be increased by 66.8 kPa,and the stress limit value of the subgrade surface is 1.29 times of the normal value.The softening state of the ballast bed to a state smaller than the modulus of the surface layer of subgrade bed has a significant impact on the stress increase of the subgrade bed,which increases by 9kPa.The change of subgrade bed modulus has no obvious effect on the stress distribution of subgrade.3、Discussion from the subgrade bed failure mode,analysis of the subgrade bed design method based on strength control and strain control.It is recommended to use the strength control criterion for the surface layer of the heavy-haul railway subgrade bed,and the total thickness of subgrade bed,namely the thickness of subgrade bed,should be determined by strain control method.The surface layer of the 35t~40t heavy-haul railway subgrade bed should be 0.8m,and the thickness of subgrade bed should be determined according to the performance of packing.The optimal design is 2.7m,and the minimum design is 0.7m.4、The structure of high strength improved soil subgrade and the foamed light-weight soil transition section were proposed and verified by scale model test.The high strength improved soil subgrade structure uses 0.3m grade gravel and 0.5m high strength improved soil as the surface layer of subgrade bed.The surface layer of the foamed light-weight soil transition section is made of 0.7m thick grade gravel,0.2m two cloth and one film sand cushion,and the bottom layer of subgrade bed adopts 2.6m foamed light-weight soil.The scale model test shows that the stress distribution law of the subgrade is basically consistent with the simulation analysis,the dynamic deformation and the cumulative plastic deformation are small,and the overall structure is reasonable.