PURPOSE: To insert a water impermeable sheet in a linear groove surely with an extent of surface to a designated depth, to decrease the number of joint parts so as to improve the work efficiency of joint construction and improve water impermeable performance, and to reduce the width of the linear groove to the upmost so as to minimize the quantity of excavated soil and waste muddy water.

CONSTITUTION: A sheet roll 21 is inserted in its erected state in a start hole 22. Starting is conducted from the start hole, injection of water jets 14 from nozzles of a force-feed tube 12, pumping by a drain pipe 8 and mucking by an auger 9 are simultaneously executed to advance in a linear groove 15, and a water impermeable sheet 20 is drawn from the sheet roll into the linear groove and expanded.