CONSTRUCTION METHOD OF COMPOSITE PILE, DIAMETER ENLARGING DEVICE AND INTER-PILE CUTTING DEVICE

PROBLEM TO BE SOLVED: To provide pile body foundation structure of high quality, applicable to a large-scale steel pipe sheet pile foundation and a composite sunk well foundation and allowing the efficient construction of a composite pile with an upper pile formed of a steel pipe pile or a steel pipe sheet pile and with a lower pile formed of a diameter-enlarged cast-in-place concrete pile. SOLUTION: A pile hole 6 for the cast-in-place concrete pile of the lower pile is excavated down to the prescribed setting depth of a support layer continuously with the removal of sediment inside a steel pipe sheet pile so as to have almost the same diameter as the inner diameter of the steel pipe sheet pile 5 of the upper pile. The diameter enlarging device 10 is then hung into the hole bottom part of the pile hole 6, and a hole wall is cut by the diameter enlarging device 10 to enlarge the diameter of the pile hole, thus forming the pile shape of the composite pile with the lower pile enlarged in diameter compared with the upper pile. Lower pile reinforcement arrangement, concrete placing and concrete filling of the upper pile are then carried out to complete a pile body.