Subcritical Crack Growth of Shirahama Sandstone in Water with Various Electrolyte Concentrations
Yoshitaka NARA, Naoki HIROYOSHI, Tetsuro YONEDA and Katsuhiko KANEKO
Abstract:Knowledge of subcritical crack growth is essential to ensure the long-term integrity of engineering structures in a rock mass. It has been found that subcritical crack growth in rock is affected by surrounding environmental conditions. In most cases, rock found underground is saturated by water. 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 Shirahama sandstone in distilled water and in sodium chloride solutions with various concentrations using the Double Torsion method. We show that the crack velocity was the highest in distilled water and the lowest in sodium chloride solution with a concentration of 1.0mol/l. This result indicates the retardation of subcritical crack growth in Shirahama sandstone in sodium chloride solutions of 1.0mol/l. With increasing the electrolyte concentration, the width of the electric double layer on the surface of a solid decreases, which causes the decrease of the repulsive force acting on the crack surface. This leads to the decrease of the crack velocity up to the concentration of 1.0mol/l. On the other hand, when the concentration is higher than 1.0mol/l, the crack velocity increased. This is probably caused by the nucleation of microscopic defects on the boundary between clays and solid mineral grains, such as quartz and feldspar. It can be concluded that electrolyte concentration affects subcritical crack growth by decreasing the width of the electric double layer and compacting clays. Key Words:Subcritical crack growth, Double Torsion method, Sandstone, Clay, Salt water, Electric double layer