To block a water spouting spot by lowering the ground-water level when high-pressure water spouts in an underground excavation surrounded by sheet piles due to the wall surface of a sheet pile or boiling.

When high-pressure water spouts in an underground excavation surrounded by sheet piles due to the wall surface of a sheet pipe or boiling, an opening is made through the wall surface of the sheet pile near the spouting spot and a stop valve is attached to the opening and, at the same time, the ground-water pressure behind the sheet pile is lowered by moderately opening the valve. After the pressure is lowered, the water spouting spot is blocked. Consequently, even at such a location that the digging of a deep well is difficult due to buildings or other structures on the ground in the periphery of the excavation, the spouting of high-pressure water due to the underground water on the back of the sheet pile can be blocked quickly, inexpensively, and surely. In addition, it becomes unnecessary to urgently dig a deep well in the ground behind the sheet pipe in the middle of excavation work as before.