MARUTAI DOBOKU

By installing a special blade on the tip of a casing, rotating the casing tube around the perimeter and then by indenting it, it is possible to drill through underground obstacles, boulders or even bedrocks. A hammer grab bucket is normally used for drilling inside the casing. A chisel, down-the-hole hammer, or rock auger may also be used in some cases. The characteristic is quite similar to all casing method; however, this method enabled extraction of underground obstacles, large diameter boulder or drilling of bedrock, whereas, it was not possible so with "injection" and "vibration" methods.

Characteristic

1. By giving the strong rotation power, it is possible to drill the bedrocks and boulders, and cut steel reinforced concrete
2. In drilling of boulders, a hammer-grab-bucket grabs and extracts them
3. Because the casing tube rotates 360 degree, higher verticality is obtainable, being superior in friction cut compared to the conventional vibration method, and great deep drilling is possible
4. By using the casing tube throughout the length of the borehole, pile shape is easier ensured to avoid porous wall collapse and damage to the neighboring structure
5. Easier to evaluate the drilling ground

Drilling

Erection of steel reinforcement

In this method, weight is applied with a drill collar onto the wing bit or roller bit installed on the point of a drill pipe, and then a drill string is rotated with a rotary table or top drive (power swivel) to drill the bedrock. Debris is extracted continuously with a pump suction or an air-lifting method to the ground surface.
For protection of porous wall, s standpipe is placed on the wall surface. In the deep area below the standpipe, protection is kept by the water head difference between the level of mud-cake and residue water formed by buddy water in the porous wall and underground water.

Characteristic

1. The drill diameter may be freely selected. It is possible for bedrock drilling with size between 0.8~3.0m
2. Because of a use of water, it is a suitable method for works on water. With an air-lifting method, it is possible for great deep drilling of over 100m
3. 19.6kPa of still water pressure is applied over the porous wall to stabilize it; no extensive casing is necessary
4. A method with minimum noise and vibration

Drilling

Concrete Placement