EXCAVATION METHOD OF HAMMER GRAB, AND HAMMER GRAB

PROBLEM TO BE SOLVED: To provide a hammer grab that can clamp a shell before the start of closure to securely prevent the shell from floating, and is adjustable in pressing force for clamping.SOLUTION: There is provided an excavation method of a hammer grab including: positioning an up-down moving body 12 at a predetermined position above a base of a clamp fitting arm 6, slackening a wire 16 to make the hammer grab H freely fall; lowering the up-down moving body 12 with inertial force by abutment of a tip of the shell against an upper surface of the foundation and moving the clamp fitting arm 6 outward in a radial direction of a casing C; bringing a clamp abutting part 10 into contact with an inner periphery of the casing C for clamping; and moving the up-down moving body 12 to an unclamping position by sending oil to an unclamping cylinder 18 when the shell is closed by scooping soil due to traction from the wire 16.