| 摘要 |
PROBLEM TO BE SOLVED: To provide an improving method capable of efficiently improving soft ground and a screw shaft used in the method. SOLUTION: In this method for improving soft ground, a hole 11 is digged in the soft ground by the screw shaft 13 provided with a spiral blade 17 on its outer peripheral face, then the screw shaft 13 is reversely rotated, an improving material for solidifying and improving the ground is charged into the hole 11, and a component of force in the radial direction is given to the improving material by the reverse rotation of the screw shaft 13 when compressing the improving material by the screw shaft 13 to compress the improving material in the vertical direction parallel with an axis of the hole 11 and in the radial direction. The screw shaft used in the method is provided with the spiral blade 17 on an outer peripheral face of a rotary shaft 15, and a plurality of rotary blades 21 parallel with a shaft axis of the rotary shaft 15 or inclined slightly for the shaft axis are provided on the outer peripheral face at a tip of the rotary shaft 15.
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