| 摘要 |
PROBLEM TO BE SOLVED: To prevent a head end of a coupler projection of an earth rod from colliding against a driving harpoon and to make it of a low cost material. SOLUTION: A shape of a fitting hole of an earth rod of a driving harpoon 1 is made in two stages, a coupler projection 31 of the earth rod 3 is shaped not to directly make contact with the driving harpoon, and stroking force is transmitted from a shoulder part 32 of the earth rod to a stage part 23 of the fitting hole of the driving harpoon 1. Additionally, cost is reduced by making the driving harpoon by casting, and when the earth rod cannot be driven to a specified depth due to an obstacle, etc., the earth rod is pulled up by leaving the driving harpoon underground, and it is possible to drive the earth rod at a different site by using a new driving harpoon favourably in cost.
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