Model tests on the long-term settlement of pile-net composite structure subgrade for high-speed railways

The settlement control of the high-speed railway subgrade plays an important role in comfortable and safe running of high-speed train. With the growth of operation time, the long-term settlement of railway in soft subgrade has been concerned. Based on the Xuzhou-Shanghai section of Beijing-Shanghai high-speed railway, the model tests on the pile-net composite structure subgrade under dynamic loading were carried out, and the variation rules of subgrade settlement, stress ratio of pile-soil, and axial force distribution were obtained. The results show that in the first 1000 loading cycles, the subgrade settlement increases with loads significantly, and then it reached a constant value. The deformation of soil is larger than that of pile at the upper pile position, the negative friction resistance appears, and the neutral point of pile is located near 2/3 pile length away from the pile top. The axial force of pile increases with the increase of the cycles of loads, when the loading cycles reach 40000, the axial forces doesn't obviously increase.