| 摘要 |
PROBLEM TO BE SOLVED: To effectively perform preliminary reinforcement of the natural ground. SOLUTION: To perform excavation by explosion of explosive 14, a blast hole is bored. A bolt member 28 is inserted into the front end of the blast hole 20a and the explosive 14 is charged into the rear end of the blast hole 20a. A cavity 22 in the blast hole 20a is filled with a filler 24 made of jelly-like material, as is a short blast hole. The bolt member 28 is provided on its outer peripheral surface with a mechanical working part 32 whose diameter can be increased. Upon explosion of the explosive 14, the mechanical working part 32 whose diameter can be increased is elongated by detonation pressure resulting from the explosion and the inner peripheral diameter of the bolt member 28 is increased, so that the outer peripheral surface of the bolt member 28 is closely contacted with the inner peripheral surface of the long blast hole 20 and anchored thereto.
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