EXCAVATING METHOD FOR HARD ROCK BED

PURPOSE:To improve efficiency by excavating a base rock with a small hole continued in a predetermined digging surface or providing a space by a rotary impact machine drill thereafter crushing the rest part excavated by a vibrative impact. CONSTITUTION:An edge point part is formed by a point end having a protruding guide 1a in the center and a chip 1c of cemented carbide metal or the like implanted in a peripheral end surface 1b. Next attaching a machine drill to a peripheral edge surface 2b of a final bore 2a in a pile 2 of small section, stone crushing, giving fine vibrative percussion and turning force, successively excavates a relatively shallow small hole 3a, and a similar small hole 3b is continuously cut in a plane plate inside the hole 3a. And in the case of excavation of large section, first a final bore 4a cuts in its peripheral edge part the small hole 3a in a lotus root shape providing a space, forming the total volume about half the hole, and the rest 5 is crushed and excavated by giving impact and vibration to a free surface 4b. In this way, profitable excavation can be attained.