SOFT GROUND STABILIZATION

PROBLEM TO BE SOLVED: To improve a soft ground efficiently into a hard one even in a deep section by loading vacuum pressure in to an improved ground through a vertical drain material and a water-conveyance material connected to the vertical drain material. SOLUTION: The load of vacuum pressure is continued from a vacuum pump 12 through a water-conveyance material 14 so that the insides of vertical drain materials 11 reach 0.4 atmospheric pressure or less, the whole region of an improved ground A is used as a decompression region and the increase of consolidation and strength is promoted, cracks C are generated from the deformation of boundary sections B1 among the ground A and non-improved grounds B, and the decompression region isolated from peripheral sections is manufactured in the improved ground A. Accordingly, not only the improved ground but also a deep section exceeding 20 m are consolidated surely and the increase of strength is promoted, and a hard ground can be improved efficiently. The ground can be improved more efficiently by the covering of the top face of the improved ground A with a synthetic-resin film prior to the load of vacuum pressure, the installation of a cut-off wall 15 to the peripheral section of the improved ground A, intermittent decompression load, load continuation after the generation of the decompression region, or banking or the like before and after the preparation of the decompression region.