| 摘要 |
<P>PROBLEM TO BE SOLVED: To evade deposition of excavated sediment in a rotation space part held in order to rotate a casing side engaging part in an opposite direction to a bit side engaging part and release an engaged state, and to smoothly detach and pull out a drilling casing from a tip bit, in a soil improvement method of improving soil by injecting a chemical by a double packer system. <P>SOLUTION: Other than a plurality of jetting ports 15 made to pass through and opened from a valve chamber 19 to a tip of a bit body part 23, a tip bit 11 is provided with a washing port 20 passing through a peripheral wall part of a valve chamber 19 at a part more on the tip side than an enclosed position of a valve body 18 closely attached to a valve seat part 19b. The washing port 20 is opened toward a rotation space part 29 held on the rotation side in the opposite direction of a casing side engaging part 22, for allowing the casing side engaging part 22 to be rotated in the opposite direction of one direction X to a bit side engaging part 21 and detached, and is capable of discharging washing water to the rotation space part 29. <P>COPYRIGHT: (C)2012,JPO&INPIT |
