METHOD OF PRODUCING A WATERPROOF SHEET FOR A TUNNEL AND ITS USE

Method of producing a waterproof sheet for a tunnel which is to be built by a cut and cover tunneling method comprising a base sheet containing a synthetic resin which is an ethylene-vinyl acetate copolymer having a content of a structural unit derived from vinyl acetate of 30% by mass or more, and having on a surface thereof a silica-containing surface layer containing silica having a silicon dioxide content of 90% by mass or more, the method comprising a step of coating the base sheet with a silica dispersion liquid and drying under heating to form the silica-containing surface layer, the silica dispersion liquid comprising (i) to (iii): (i) silica having a silicon dioxide content of 90% by mass or more, dispersed in (ii) an organic solvent exhibiting dissolution action on said ethylene-vinyl acetate copolymer of the base sheet, and (iii) a thickener having affinity with the synthetic resin of the base sheet, the thickener being an ethylene-vinyl acetate copolymer having a content of structural unit derived from vinyl acetate of 30 to 90% by mass, the silica in the silica-containing surface layer being present in a content of from 30 to 200 mg/cm 3 , the silica-containing surface layer being formed over a depth of from 5 to 30 µm from the surface of the waterproof sheet, the waterproof sheet having a tensile breaking strength of 20 MPa or more, a tensile breaking elongation of from 10 to 50%, a tear strength of 50 N or more and a watertightness on deterioration in evenness or levelness of 10 mL/day or less, and a mortar adhesion strength of 15 N/cm or more.