SOFT GROUND IMPROVING METHOD IN COLD DISTRICT

PROBLEM TO BE SOLVED: To provide an improving method for soft ground capable of providing satisfactory construction efficiency and suppressing equipment cost. SOLUTION: This improving method for soft ground has a pretreatment process in which first water passing materials 12, 13 communicating with a first pump are arranged on a surface of the ground to be improved before a cold season comes, the water passing materials are covered with a first sheet 11, a negative pressure condition is created under the sheet by the pump to pump up underground water, and the underground water is maintained in the ground of a surface layer to be improved until a cold season comes to prevent freezing of the surface layer ground. Furthermore, it is composed of a process in which ground for construction 20 is prepared on the first sheet after the pretreatment process, a process in which a drain material 28 is placed in substantially vertical direction on the ground for construction, a process in which a second water passing material 23 is arranged on the ground for construction, a process in which a second sheet 21 is spread, a process in which a pump 25 communicating with the second water passing material is arranged, and a process in which water and gas in the ground are discharged by the pump.