| 摘要 |
PROBLEM TO BE SOLVED: To provide an excavation method which can level a bottom surface of a hole to be formed. SOLUTION: In the excavation method, a surface to be excavated is excavated vertically downward by means of a drill 20 of excavation equipment 10 so as to form the hole. In this case, an outer shape of a drill bit 21 of the drill 20 can be changed between a first outer shape tapered toward a lower end, and a second outer shape having a lower end formed as a horizontal plane. In the formation of the hole, when the drill bit 21 firstly employs the first outer shape, the surface to be excavated is excavated by using the drill bit 21 so as to form the hole with a cone-shaped bottom surface (S14). Subsequently, the outer shape of the drill bit 21 is changed into a second outer shape from a first outer shape (S16). After that, when the drill bit 21 employs the second outer shape, the surface to be excavated is further excavated by using the drill bit 21 (S18). Thus, the shape of the bottom of the hole is changed into a flat shape from a cone-like shape. COPYRIGHT: (C)2010,JPO&INPIT
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