Abstract: An excavation rod of a ground improvement apparatus is provided with an excavation blade and plural steps of agitation blades above the excavation blade. A corotation prevention blade which does not rotate during the excavation vertically and rotationally, is provided between the excavation blade and the agitation blade and plurality of downwardly projecting fingers are secured to the corotating prevention blade.

Abstract: This invention relates to a multi-rods type of ground improvement apparatus to be used in ground improvement work. There are provided plural rods in parallel, excavation blades are mounted to the ends of the rods, the rods are provided with injection openings for a solidifying agent, and at least one link arm is loosely mounted to connect the rods. Between the excavating blades and lowest positioned agitating blades, a still or stationary corotating prevention wing is loosely mounted and both ends of the wing are extended so as to be aligned with ends of the excavation blades positioned at opposite sides of the plural rods.Clods dug by the excavation blades are fully crushed between the rotating excavation blades and the still or stationary corotation prevention wing and well mixed with the solidifying agent.Further, by providing screw type of pilot heads at the ends of the rods, advancing of the rods into the ground is improved when the ground is excavated.