PURPOSE: To reduce a discharge quantity of environmentally pollutive earth and sand containing cement quality and a ground stabilizing liquid, and improve vertical accuracy of an excavating hole by excavating the inside of a partial casing having a boring edge and a chemical injection pipe in a dry system.

CONSTITUTION: Excavating soil is discharged by excavating the inside of a partial casing 1 which has a boring edge 1D and a friction cutter 1B on the tip and is composed of a steel pipe 1A having a chemical injection pipe 1C on an outer peripheral surface. While injecting a ground stabilizing liquid, a hole is bored in the ground under the partial casing 1, and a ready-made pile or a soil cement pile reaching a support layer is installed. While pulling out the partial casing 1 by rotating it in the circumferential direction, a chemical is injected into the peripheral ground from the tip of the chemical injection pipe 1C. The partial casing 1 is rotated in the circumferential direction, and it is vertically pressed in with excellent accuracy. Since the chemical is injected while pulling out the partial casing 1, the peripheral ground of an installing pile is improved.