| 摘要 |
PROBLEM TO BE SOLVED: To provide a hole forming method for a concrete structure that can securely form a cylindrical hole having a diameter-increased part at a bottom part in a concrete structure.SOLUTION: A method of forming a cylindrical hole having a diameter-increased part at a bottom part in a concrete structure comprises: the processes of: forming a prepared hole 21 having an inner diameter equal to that of the cylindrical hole in the concrete structure 20; using a diameter-increasing drill which has a first driving shaft 10 supported rotatably at a base part 11 and has a second driving shaft 12 coupled to a tip part of the first driving shaft to be freely bent and also energized in a bending direction, inserting the diameter-increasing drill into the prepared hole, holding the base in contact with a prepared hole inner surface to hold an attitude of the diameter-increasing drill, bending the second driving shaft from the first driving shaft with energizing force, pressing a diameter-increasing bit 13 fitted to the second driving shaft against a bottom part inner surface of the prepared hole, and driving the first driving shaft so as to form a diameter-increased part 22 at a bottom part of the prepared hole.SELECTED DRAWING: Figure 1 |
