Abstract: The base reaction and deformation features are analyzed based on measured data, according to model test of variable-length CFG pile composite foundation for frame-tube structure. Some conclusions are drawn as follows. First, under the working loads, longitudinal deflection of medial axis of foundation is 0.25‰, and longitudinal deflection of diagonal direction of foundation is 0.21‰, as adopting long piles to strengthen the area of core-tube, short piles to weaken the area of outside frame column, and middle length piles between area of core-tube and area of outside frame column to transit. Second, under the working loads, the pile top stress of core-tube is obviously higher than pile top stress of outside frame column. Pile top stress of core-tube area is relatively uniformly. The biggest pile top stress is on the corner pile, next is on the side pile, and the smallest is on the center pile in the area of core-tube. Soil stress between area of core-tube and area of outside frame column is little difference. The distribution of soil stress is even distribution both in area of core-tube and outside frame column, and bearing capacity of soil among piles of three areas all can play fully. Third, under the working loads, the highest stress of the base force is in area of the core-tube, distributes relatively uniformly and shows linear distribution basically. Base reaction is gradually weak from area of core-tube to area of outside frame column. The lowest stress of the base force is in area of outside frame column, its distribution is relatively uniformly and basically line-shaped. The base reaction basically shows basin-shaped. Distribution of base reaction is obviously related with composite modulus, which is basically linear relationship.

Key words: CFG pile composite foundation, frame-tube structure, base reaction, deformation characteristic, model test