| 摘要 |
PROBLEM TO BE SOLVED: To reduce construction cost, by easily extracting and collecting a casing top and a casing pipe from an excavation hole.SOLUTION: A casing top 2 is coaxially installed on the tip of a casing pipe 1, and in a tip part of the casing top 2, a ring bit 3 having in an inner peripheral part an abutting object part 3B of an inner diameter smaller than the casing pipe 1 and the casing top 2, is rotatably locked-installed on the tip side around the axis O of the casing top 2, and an inner peripheral part of the ring bit 3 is provided with an abutting part 4A capable of abutting on the abutting object part 3B, and an inner bit 4 of an outer diameter smaller than an inner diameter of the casing pipe 1 and the casing top 2 is integrally and rotatably engaged with the ring bit 3 by being inserted from the rear end side, and the outer diameter of the casing top 2 is set within a range of ±3 mm to the outer diameter of the casing pipe 1. |
