Field Test Study on the dynamic response of the cement-improved expansive soil subgrade of a heavy-haul railway

To study the adaptability of cement-improved expansive soil as a heavy-haul railway subgrade filling material, based on a test section of the Inner Mongolia-Jiangxi railway cement-improved expansive soil embankment, cyclic vibration tests were conducted under different axle load, train speed and service environment conditions. By analysing dynamic parameters such as dynamic stress, acceleration and dynamic displacement at different subgrade positions, the train dynamic load distribution and attenuation law in the cement-improved subgrade were obtained, and the axle load, train speed and rainfall effects on the dynamic cement-improved subgrade response were analysed. The dynamic parameters are linearly attenuated along the subgrade depth and lateral direction in the same filling structure layer. The dynamic stress attenuation at the bottom of the subgrade surface layer is approximately 49%, and that at the bottom of the lowermost subgrade layer is 76%. The attenuation of the coarse-grained filler is larger than that of the cement-improved expansive soil; the dynamic parameter values at various subgrade positions increase linearly with increasing train speed and axle load. The closer the vibration source is, the larger the dynamic parameter increment; the change in the subgrade water content has a certain effect on the subgrade's dynamic response characteristics. In the immersed state, the subgrade dynamic parameter value is greater than the natural state value, and the subgrade accumulated deformation will be promoted after subgrade immersion in water.