SOIL IMPROVEMENT METHOD AND SOIL IMPROVING DEVICE

PROBLEM TO BE SOLVED: To provide a soil improvement method and a soil improving device which can construct a high strength column while suppressing the usage amount of a solidification material liquid even in loam soil ground or organic soil ground, have less impact on peripheral ground, prevents the generation of banking to be industrial waste, and is excellent in constructibility.SOLUTION: A soil improving device 1 includes: an excavating-agitating head 2 having a drilling blade 3 at the tip as well as a blade 5 and a corotation-preventing blade 4 above the drilling blade 3; and a screw rod 7 connected to the excavating-agitating head 2 and having a screw blade 8 in the outer periphery. A lower discharge opening 6 for discharging solidification material liquid is provided in the tip of the excavating-agitating head 2. An upper discharge opening 9 for discharging the solidification material liquid is provided just under the lower end of the screw blade 8. In an excavation step, after removing earth and injecting the solidification material liquid from the lower discharge opening 6, the solidification material liquid is discharged just under the lower end of the screw blade 8 while removing earth by the screw blade 8 in the step of pulling up the soil improving device 1 so as to agitate and mix with sediments.