CUT-OFF METHOD FOR JOINT IN UNDERGROUND STRUCTURE AND CUT-OFF STRUCTURE

PROBLEM TO BE SOLVED: To provide a cut-off method for a joint in an underground structure, which is good in follow-up capability at a corner portion or a joint portion, is not deteriorated or changed in the long term, and has high reliability, and to provide a cut-off structure. SOLUTION: According to a cut-off method for a joint 5 of an underground structure 1 constructed by combining predetermined members 2 with each other, a cut-off material formed of a water-swelling clay composition which has an internal core member 7 and an adhesive surface, is arranged at least one portion of the joint 5, and thereafter a joint surface of one of the members concerned and a joint surface of the other member to be adjacently combined with the one member are tightened up, whereby the water-swelling cut-off member is press-fitted between the joint surfaces to cut-off water. When a clearance is generated at the joint 5, due to a restoring force and swelling of the water- swelling cut-off material, water is cut off. A cut-off structure at the joint 5 is constructed such that cut-off material setting portions 4 of the respective joint surfaces pinch the cut-off material comprised of the external water-swelling clay composition 6 and the internal core member 7 having the restoring force.