It is of significant importance to safely isolate the radioactive wastes from the human environments. Entombment of the wastes in deep subsurface may be a plausible solution on this issue, and will be adopted in the countries where the nuclear power plants are in operation. Before burying them in the targeted rocks, the longterm evolution of the mechanical and the hydraulic properties of the targeted rocks should be predicted with a certain precision. To this end, in this study we examined the change of the apparent secant elastic modulus and the permeability of a single fracture in the Berea sandstone and the Horonobe mudstone samples under the relatively high temperature and confining pressure conditions. The apparent secant elastic modulus of the mudstone increased with the increase of the holding time and specifically, the values at 90 ºC were greater than those at 25 ºC, while that of the sandstone little increased with time. In contrast, the permeability of both the mudstone and sandstone samples monotonically decreased with time, and the rates of the permeability reduction were close among all the samples. The increase of the elastic modulus and the decrease of the permeability may be attributed to the chemomechanical processes such as pressure solution and the mechanisms explaining the changes should be clarified. Although the mechanisms are still ambiguous, the increase of the elastic modulus and the permeability reduction with time may improve the integrity of the targeted rocks.
