Abstract: The present invention aims to provide apparatus and method for determining non-circular figure to drill boring holes having a regular N-polygonal cross sections while retaining the advantage of the turning operation. For boring a boring hole (H) with a cross-sectional shape of a regular N-polygon having vertexes of N in number, a boring tool (T) having a cross-sectional shape of a regular (N?1)-polygon which is inscribed on the regular N-polygon of the boring hole is driven to rotate at a certain rotational speed around its center (G) and revolve at a certain revolving speed along a circle (R) which is concentric to the boring hole center (0) and has a certain radius. The boring tool (T) may be replaced with a jet of fluid. A boring tool (T) with a regular (N+1)-polygonal contour may be used instead.

Abstract: At least one guide shaft is equipped on one or both sides of a plurality of drilling shafts arranged on a line; and a jet nozzle is equipped with said guide shaft. A multi-shaft drilling unit, equipped with preferably three auger shafts, is used to develop a continuous wall under the ground. In such a unit, a housing for maintaining a pitch between the auger shafts includes a housing comprising: a primary gear rotating around the central auger shaft; a pair of secondary gears engaging with the primary gear; a primary bevel gear integral to the primary gear; a secondary bevel gear engaging with said primary bevel gear and fixed to a rotary shaft which rotary shaft is perpendicular to a straight line connecting the center lines of auger shafts; and cutters fixed at both ends of the rotary shaft.

Abstract: A multi-shaft drilling unit having three auger shafts for developing a continuous under ground wall and comprises a housing for retaining pitch between the auger shafts, the housing comprising, primary transfer gears rotating around a central auger shaft, secondary transfer gears engaging with the primary transfer gears, a tertiary transfer gear connected to the primary transfer gear, a quaternary transfer gear connected to the tertiary gear and fixed to a rotary shaft orthogonally crossing a straight line connecting auger shaft centers, and cone-shaped cutters expanding the diameter outward and fixed on both ends of the rotary shaft. The cutters cut off a triangular convex and form a continuous wall unit of which both ends form a semicircle and both sides form a straight line and can be formed in subsoil.

Abstract: The present invention relates to a method for improving the ground of a large area. The method comprises the steps of inserting a pipe into a hole previously dug in the ground, injecting a high pressure liquid and a ground improving injection liquid from an injecting apparatus attached to the tip of the pipe, drawing up the pipe, grouting the ground, and injecting the ground improving injection liquid to thereby form an underground columnar consolidation body for improving the ground. The drawing-up operation of the pipe is executed while applying vertical vibration to the pipe. Thus, a consolidation body of a large area for improvement of the ground is obtained without concave and convex portions.

Abstract: The present invention relates to a method for improving the ground of a large area. The method comprises the steps of inserting a pipe into a hole previously dug in the ground, injecting a high pressure liquid and a ground improving injection liquid from an injecting apparatus attached to the tip of the pipe, drawing up the pipe, grouting the ground, and injecting the ground improving injection liquid to thereby form an underground columnar consolidation body for improving the ground. The drawing-up operation of the pipe is executed while applying vertical vibration to the pipe. Thus, a consolidation body of a large area for improvement of the ground is obtained without concave and convex portions.

Abstract: The present invention relates to a method of improving the ground of a large section area. A double pipe, having a first nozzle directed in the lateral direction and a second nozzle surrounding the first nozzle, is inserted into a hole dug in the ground. A ground improving agent is injected at high pressure from the first nozzle through one pipe of the double pipe. A reproduced slurry, obtained by reproducing grouted slimes, is injected from the second nozzle through the other pipe of the double pipe at a lower pressure than the pressure of the ground improving agent. While rotating, the double pipe is lifted up from under ground. The ground improving agent, injected at the high pressure, is surrounded by the reproduced slurry injected at the lower pressure. The frictional resistance between the ground improving agent and the sediments is reduced, the arrival distance of the ground improving agent is increased, and the abrasive effect is obtained.