Abstract: The design of CFG piles with caps applied in expressways in deep soft soil ground differs from that of architectural engineering.There is no appropriate criterion at present.The upper building foundation of construction engineering is rigid and rigid load is imposed on the ground.However,the railway subgrade bears directly the roadbed load and the dynamic load of trains which is flexible load.So under the condition of flexible foundation,the optimization of cushion thickness of CFG pile composite foundation with caps is of great significance.In field load tests,rubber plates are used to simulate the flexible foundation of high-speed railway.Through change of cushion thickness,researches on the settlement deformation and load sharing properties of CFG pile composite foundation with caps are conducted.