PURPOSE: To control the level of ground water in the back side of sheathing wall by utilizing the head of natural water by a method in which an infiltration pipe and a communication pipe whose top is provided with a vertical pipe for watching the level of ground water are buried in the back side of the sheathing wall.

CONSTITUTION: A concrete continous underground wall 1 is formed, excavation is made, and then the sheathing timbering for cut beams is orderly provided. Excavated holes 4 are provided at given intervals along a design ground-water lowering level A in the underground wall 1, and an infiltration pipe 5 is inserted into the holes 4. Other excavated hole 11 is provided at a proper distance from the excavated hole 4 of the underground wall 1, and a communication pipe 13 whose top is provided with a vertical pipe 12 for watching the ground water level is inserted into the hole 11 and buried. While watching the ground water level by the vertical pipe 12, a valve 9 is opened or closed to discharge the ground water in the back side from a drain pipe 10, whereby controlling the lowering of the ground water level.