| 摘要 |
PROBLEM TO BE SOLVED: To provide an excavation drill capable of effectively discharging mud in which excavated soil and fragments are mixed with water onto the ground. SOLUTION: An internal pipe 2 is inserted into an external pipe 1, a circular outer bit 4 is attached to the lower end of the external pipe 1, and an inner bit 5 is attached to the lower end of the inner pipe 2. Three wide and deep grooves 5a extending in the longitudinal direction of the pipe are provided in the inner bit 5, and a diametrally broadened part 5b in the circumferential direction is formed in the middle of the lower part of groove 5a and further, a stepped part 4b to be housed in the groove 5a is projected at the inner periphery of the outer bit and inserted in the diametrally broadened part 5b of the groove 5a and fixed to transmit the rotation from the inner bit 5 to the outer bit 4. In this way, the ground is excavated so that the space of the groove 5a confronts the excavating ground at substantially right angles.
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