| 摘要 |
PROBLEM TO BE SOLVED: To rest a first revolving body at an optional position by providing a brake device constituted of a ring-like disk section provided on the first revolving body and a pinch section arranged below a scaffold. SOLUTION: A brake device 35a constituted of a ring-like disk section 36 and a pinch section 37 capable of pinching the disk section 36 is provided below a first revolving body. The disk section 36 rotated together with a revolving body main body 31a is pinched by the pinch section 37 arranged below a scaffold 2, the rotation of the disk section 36, i.e., the rotation of the main body 31a, is stopped by the frictional force generated at that time. The number of disks of the brake device 35a is determined according to the rotary load applied to the first revolving body so that a brakeable load sufficiently exceeds the rotary load and the first revolving body can safely rest. The first revolving body receives excavation reaction without being rotated, and an excavation can be made all the corners regardless of the position and direction of an excavation section.
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