PURPOSE: To increase effective shooting distance of a grout material by a method in which a space is drilled in the ground by injecting a high-pressure water from one nozzle, and a grout material is injected into the space from the other nozzle.

CONSTITUTION: A grout material is injected under water from the first nozzle 10 to dig out the ground B while interlocking an injection tube 2, a high-pressure water tube 3, an air tube 4, and a soil discharge tube 5 with the upward movement of an outer tube 1 to form a solidified soil upwardly, and also the ground B is excavated by injecting high-pressure water from the second nozzle 14 to form a space 22, where high-pressure air from the air tube 4 is filled up in the space 22 to prevent the degradation of the surrounding ground. Since the ground to be excavated by the first nozzle 10 is already dug out horizontally by as much as a given distance by the second nozzle 14, the effective shooting distance of grout material to be jetted from the nozzle 10 is increased and the horizontal distance of the solidified soil is thus expanded.