SOIL IMPROVEMENT METHOD

PURPOSE:To draw the peripheral soft soil into the discharging soil zone and prevent the excavation from badly affecting the periphery, by discharging the original soil gradually by the volume corresponding to the delivered solidifying agent at the same time when the solidifying agent is delivered and mixed and agitated on pulling out a rotary shaft body. CONSTITUTION:A rotary shaft body is constituted of a triple-tube composed of an inner pipe 1, an intermediate pipe 2, and an outer pipe 3, which can be changed to an optional rotary direction and a revolutional number respectively. The lower ends of the intermediate pipe 2 and the outer pipe 3 are made a little shorter than the inner pipe in turn respectively. A lower stage excavation and agitation blade 5 and an upper stage agitation blade 6 are fitted to the lower ends of the inner and intermediate pipes 1, 2 respectively. A soil-discharging spiral blade 7 is protrusively formed at the external periphery of the outer pipe 3 and delivery outlets 4, 8 for a solidifying agent slurry are provided at the lower end. After the rotary shaft body has been inserted to a specified depth of a soft ground, the solidifying agent is deliver ed from the outlets of the outer pipe 3 and the outer pipe is rotated reversely. The whole rotary shaft body is pulled out gradually from the ground while rotating the inner pipe and the intermediate pipe to different direction from each other, in order to simultaneously mix and agitate the soft ground with the solidifying agent' and also remove the soft ground to the outside.