PURPOSE: To prevent the occurrence of land subsidence by a method wherein a forced feed means to feed with a pressure underground water to a ground is arranged at a first communicating means to intercommunicate an intake part and a ground and a second communicating means to feed underground water, fed with a pressure, to a drainage part is arranged.

CONSTITUTION: Underground water in a confined water-bearing stratum 25 on the cutting excavation side of a continuous underground wall 10 flows through an intake part 15 by its own pressure or by the suction force of a storage pump 13 and is purified to some extent by a filter 15a and flows through a communicating pipe 16 into a communicating pipe 17. Underground water flowing through the communicating pipe 17 has mixed sand mud a part of which is settled at a sand reservoir 17a for purification. Purified underground is sucked by the storage pump 13 and fed with a pressure through a filter 14 and a communication pipe 12 to a sedimentation tank 18. Underground water from which a mud content is removed in the sedimentation tank 18 is sucked through a communication pipe 19 by a forced feed pump 20 and fed with a pressure through a communication pipe 21 to a communication pipe 22. Further, sand mixed in underground water is settled in a sand reservoir 22a and underground water flows through the communication pipe 23 and is discharged through a drainage part 24 to the confined water-bearing stratum 25.