In-situ test on settlement of CFG pile-raft composite foundation in high-speed railway

To understand the characteristics of settlement and deformation of the CFG(cement fly-ash gravel) pile-raft composite foundation under embankment loads, the in-situ test on settlement and deformation is carried out in the Fengyang experimental section of the Beijing-Shanghai high-speed railway. The settlements of pile and soil of the foundation top surface, the settlements of the subgrade top surface, and the lateral displacements of the foundation are monitored by the settlement plates, the observation piles and the inclinometers, respectively. The variation laws of the settlement and deformation with the embankment height and the time are analyzed. And the hyperbolic curve method for settlement prediction is discussed. The results show that the settlements of the CFG pile-raft composite foundation increase with the filling height of the embankment and the time. The settlements tend to be stable after standing more than 6 months of subgrade. The total settlements and pile-soil differential settlements of the composite foundation are less than 15 mm and 2 mm, respectively. The maximum lateral displacement of the foundation at 1 m from the toe of the embankment is less than 4 mm. The hyperbolic curve method is feasible for the settlement prediction of the subgrade and the prediction precision is high. The total settlement, differential settlement and lateral displacement of the foundation improved by CFG piles and rafts are small, and the settlement of the subgrade quickly becomes stable. The stability of the subgrade can be improved and the construction period can be shortened by ground improvement with CFG pile-raft.