Dynamic Response Study on Speed-Increase Subgrade of Existing Railway

According to dynamic finite element method and field dynamic test on Shanghai—Nanjing main line subgrade under track irregularities and train speed 120—200 km·h-1,the study about the dynamic response of the speed-increase subgrade on existing railway is carried out.Distribution of dynamic stress on the base surface,the relationship between dynamic stress of the subgrade and train speed,the degradation laws of dynamic stress along the depth are obtained.The influence of the thickness of road bed and height of subgrade are analyzed for the dynamic stress.Results show that the dynamic stress of the subgrade linearly increased with speed-raising of the train.The dynamic stress on the subgrade appeared saddle distribution with double hump and with the depth increasing the peak of the saddle will decrease till the dynamic stress at the center of subgrade became single-hump distribution.With road bed thickness increasing,the vertical dynamic stress of the subgrade surface will be obviously reduced.The influences of subgrade height are not great to the dynamic stress of the subgrade surface,but the dynamic stress of the foundation surface can be effectively reduced.