PURPOSE: To manufacture a front end device simply at a low cost and to make a construction smooth without causing any trouble in operation by infiltrating flash-setting grout and slow setting grout with different gelation time alternately into a poor ground and the like by making use of a dual pipe consisting of an internal pipe and an external pipe.

CONSTITUTION: A dual pipe that penetrated the ground is pulled up to a specific length, sending water glass A to either channel of an internal pipe 2 and an external pipe 1, sending flash-setting hardner B1 to the rest of the channels, projecting a grouting pipe's internal pipe 2' to a hollow 7 by fluid pressure of the fluid sent to the internal pipe 2, joining the water glass A and flash- setting hardner B1 at a right angle obtain uniform flash-setting grout. After infiltrating it into big crevices in the ground around the grouting pipe, slow setting hardner B2 is sent instead of the flash-setting hardner B1, and continuous ly the water glass A and slow setting grout to be joined in the hollow 7 are infiltrated into small crevices in the ground. In addition, the flash-setting grout and slow setting grout are alternately infiltrated many times over while pulling up the grouting pipe continuously. According to the constitution, the whole ground can be hardened uniformly.