PURPOSE: To harden the whole ground uniformly by sending slow setting grout and flash-setting agent to channels of an external pipe and an internal pipe respectively and infiltrating the slow setting grout only into crevices in the ground instead of the flash-setting agent after joining them at the outside of a grouting pipe to infiltrate them into big crevices in the ground.

CONSTITUTION: The whole grouting pipe is pulled up to a position where an internal pipe 2' is pushed out, slow setting grout (A) is sent to a channel 6' by means of pressure-feed, the internal pipe 2' is pushed forward of the tip of an external pipe 1, and the slow setting grout is discharged at about a right angle along the axis from a grouting hole 4. Simultaneously, flash-setting agent (B) is discharged forward from a channel 6 through a discharge port 5, and both flows are joined crosswise. After infiltrating them into big crevices or loose parts in the vicinity of the grouting pipe, the confluence is stopped by removing the flash-setting agent (B) in a state of projecting the grouting pipe 2', and the slow setting grout is only poured into small crevices or loose parts in the ground. Furthermore, the grouting pipe is pulled up, and this operation is repeated to harden the whole ground uniformly, so that water stopping or the ground can be strengthen.