PIT MOUTH CUT-OFF DEVICE OF CASING SHAFT

PROBLEM TO BE SOLVED: To provide a pit mouth cut-off device which has a relatively simple structure, of which fitting work can be rapidly performed without a hitch and without special concern, and of which cut-off performance and workability are more excellent than those in conventional cut-off methods.SOLUTION: When installing a shaft 15, an A-part with a ring-shaped frame body 1 in which a rubber-made cut-off plate 3, rubber packings 4, 5, a holding ring 6, and a steel guard plate 7 are internally mounted is fitted in and fixedly welded to a pit mouth 16 face-cut on the shaft 15 beforehand, and a cover body 10 is mounted on the A-part so as to surround the inside of the A-part of the shaft. When a drilling machine starts or arrives, instead of the cover body 10 and the steel guard plate 7 from the A-part, a B-part consisting of a cut-off cylinder 11, with which an outward flange 11a is provided at an outside end, an outward flange 11b with rubber packings 4', 5' attached is provided at an inside end, and an injection port 12 for a water cut-off chemical liquid is provided at the trunk, is connected, and a hydrophilic polyurethane resin is injected from the injection port 12 for the water cut-off chemical liquid.