| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a hard ground excavation method which can shorten excavation operation time when a pile hole is excavated in a hard ground comprising bedrock or boulder stones.SOLUTION: A hard ground comprising bedrock or boulder stones and the like is dug down by a rotating casing 1, and in parallel with it, a down-the-hole hammer device 2 is vertically movably installed inside the rotating casing 1 in a state where its rotation is relatively restricted. A hole for inducing cracking by falling of a hammer grab is drilled in the hard ground inside the casing 1 by the down-the-hole hammer device 2 rotating about the rotation center of the casing 1 together with the casing 1. Subsequently a ring-shaped hard ground remaining around the hole for inducing cracking is crushed by an eccentric rock crushing device or the falling of the hammer grab to a size capable of being held by the hammer grab, and discharged.</p> |
