PURPOSE: To perform excavation work with good efficiency by a method in which a muddy pit is formed in the ground, expanded excavation is made over a length a specific times as much as the diameter of the pile to a given depth, a precast pile tipped with a cylindrical bag is settled down into the pit, and a solidifying fluid is injected into the pit.

CONSTITUTION: While turning an excavating rod 1 having an excavating bit 5 on its tip, excavation is made to a given depth by jetting excavating liquid from the bit. Expanded excavation is then made over a section of length at least two times the pile diameter near the given depth by high-pressure jet. The excavating fluid is replaced by a solidifying fluidizing agent C and the rod 1 is recovered while jetting the fluid C at a pressure of 20W50kg/cm2. A precast pile 10 tipped with a cylindrical bag 11 is penetrated into the muddy pit K, connected with normal precast pile 12, and settled down. The solidifying fluid C is then injected into the bag 11 to expand it.