Reaction rates of rocks to aqueous solutions is very slow, so that the contribution of chemical reaction to the strength reduction of rocks in a short timescale has not been discussed. In this study, the unconfined compression test (UCT) was conducted with rocks saturated with aqueous solutions having different pH, and the influence of the rock-solution reaction on the unconfined compression strength (UCS) of rocks in a short timescale was investigated.
To conduct the UCTs, specimens with ϕ20mm×50mm sized were prepared from two rock series, granite and sand stone. Dry specimens and wet specimens which were soaked in aqueous solutions having different pH (pH1, 4, 7, 10, 13) for four days were prepared from each kind of specimens, and the UCTs were conducted with them. In those test, the specimens which were soaked in aqueous solutions for four days were regarded as saturated.
Compared to the results under the dry condition, the UCS of sandstone specimens decreased by 52% and the UCS of granite specimens decreased by 15% under the wet condition (saturated by pH7 solution). In comparison with the results of UCTs about samples soaked in aqueous solutions having different pH, clear differences in the UCS of sand stone samples between different pH were not obtained. On the other hand, the UCS of granite samples soaked in a solution with pH7 was the maximum, and the UCS of granite samples soaked in the acid solution was slightly smaller than this maximum value. In the basic solution, the UCS was smaller than the UCS in the acid solution and became smaller as the basic solution became stronger. This tendency roughly coincides with the dependence of the quartz solution rate on pH of the solution. These results showed the UCS of rocks could be influenced by chemical environment depending on the rock type even in a short timescale.