Reducing mixing pile machine and pile forming construction method and drill pipe thereof

The invention relates to the technical field of mixing piles, and discloses a reducing mixing pile machine. The reducing mixing pile machine comprises a machine base, a tower, a mixing head and a lifting mechanism. The tower is fixed to the machine base. The mixing head is hoisted on the tower through the lifting mechanism. The mixing head comprises a drill pipe, a rotation driving mechanism and a telescopic mechanism. The drill pipe comprises an outer pipe and an inner pipe, and the inner pipe is sleeved with the outer pipe. A grout spraying nozzle is arranged on the front portion of the inner pipe. The rotation driving mechanism is connected with the outer pipe and the inner pipe. The telescopic mechanism drives the inner pipe and the outer pipe to relatively move. The outer pipe is provided with an outer pipe radial ring, and an inner pipe radial ring is arranged on the front portion of the inner pipe. A slidable transition sleeve is further arranged on the front portion of the inner pipe and provided with