Mechanical interaction between swelling compacted clay and fractured rock, and the leaching of clay colloids

摘要

We consider the interaction between a saturatedclay buffer layer an da fractured crystalline rock engineereddisturbed zone. Once saturated, the clay extrudes into theavailable rock fractures, behaving as a compressible non-Newtonian fluid. We discuss the modelling implications ofpublished experiments carried out in Sweden and more recently inJapan. Extrusion is halted either when the advancing clay frontreaches a narrow enough aperture along the fracture (relative tothe yield stress of the gel-like front), or when enough of the claymass has extruded so as to reduce the density back in the buffer,and hence the swelling pressure (which is exponentiallydependent upon density). In the latter case a relatively smallreduction in density may be sufficient. As the clay extrudes, thegel-like front may be a source of clay colloids, being sufficientlyhydrated so as to allow clay platelets to escape the matrix anddiffuse away. We show that such mass loss is limited as amechanism for leaching away the emplaced barrier, yet may stillbe significant in mobilising otherwise highly sorbingradionuclides within the buffer.