In order to ensure the long-term integrity of structures in a rock mass such as the repositories of radioactive wastes in underground knowledge of subcritical crack growth is essential. The underground water can be fresh water or salt water with different electrolyte concentrations. However, the influence of electrolyte concentration on subcritical crack growth has not been clarified. In this study, we have measured subcritical crack growth in Berea sandstone and Shirahama sandstone in distilled water and in salt water (sodium chloride solution) with various concentrations. Specifically, we have investigated the influence of the electrolyte concentration on the relationship between the stress intensity factor and the crack velocity. It is found that the electrolyte concentration affects the relation between the stress intensity factor and the crack velocity for sandstone which contains smectite, and has little influence in sandstone which contains few clays. For the sandstone containing smectite, the crack velocity decreased and the stress intensity factor increased with increasing the electrolyte concentration because of the reduction of repulsive force on the surface of expansive clay at high electrolyte concentration. It is concluded that the rock containing expansive clay becomes more stable under salt water condition.


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