Tubular pile structure used in upper-soft lower-hard stratum and reinforcing method

The invention discloses a tubular pile structure used in an upper-soft lower-hard stratum and a reinforcing method. The tubular pile structure mainly comprises a drill hole, a first preformed hole, a second preformed hole, a prestressed tubular pile and a reinforcement cage. The first preformed hole and the second preformed hole are both located in the drill hole; the first preformed hole and the drill hole are concentrically arranged, and the axis of the second preformed hole is parallel to the drill hole; the prestressed pipe pile sinks into the drill hole, and the bottom of the prestressed pipe pile extends below the soft and hard soil interface; the reinforcement cage is placed in the preformed hole, and the top of the reinforcement cage is higher than the soft and hard soil interface; and a concrete layer is poured in the prestressed pipe pile. The reinforcing method mainly comprises the steps that a hole used for pile sinking is vertically and downwards drilled, and a drilled hole is formed; a first res