PURPOSE: To prevent a wall surface strength from lowering by depositing concrete and pressing a sheet against the vertical plane of a groove after installing the sheet at a position separated by a specified distance from one surface of a reinforcement cage and lifting it down into a digging groove.

CONSTITUTION: With a water cut-off sheet 2 separated by a specified distance from one face of a reinforcement cage 1, the water cut-off sheet 2 is installed through a sheet support arm 11 and a support frame 12 extended in vertical direction. Next the reinforcement cage l is lifted down into a digging groove with the sheet 2 faced toward the outside of the groove. In this case, the sheet 2 is arranged so as to touch the outside vertical plane of the groove. Also, using a tremie pipe, concrete is deposited at the bottom of the groove and, while raising the tremie pipe, concrete is raised gradually. Then, with the sheet 2 pressed securely against the vertical plane of the groove, concrete is raised. Thus the sheet can be arranged in the boundary between an underground continuous wall external surface and the ground, production of concrete parting and water path by the sheet can be prevented, and also corrosion of reinforcement can be prevented.