Effect of water saturation on deterioration of welded tuff due to freeze-thaw action

To understand the mechanisms of rock breakdown and weathering in cold regions, the influence of water saturation on the damage of rock needs to be investigated. During freezing, water in a porous medium such as rock and concrete tends to form ice or migrate, leading to redistribution of pore water. The prediction of rock deterioration has been recognized to be quite difficult because of the migration of pore water. In this study, rock specimens were prepared from welded tuff with a degree of saturation from 0% to 95%. The specimens were frozen in a temperature-controlled chamber where the temperature varied from +5 to −18 °C and then thawed in distilled water at 14 °C. The freeze–thaw test was conducted for only one cycle including 2 h of freezing and 1.5 h of thawing. The deterioration of the specimens was examined by the changes in the uniaxial compressive strength, P-wave velocity and porosity, as well as in the appearance of the specimens. The experimental results show that when the initial degree of saturation was maintained below 60%, the above properties did not change, but when the initial degree of saturation exceeded 70%, the rock was damaged significantly. Therefore, the critical degree of saturation is about 70%. An investigation into the distribution of pore water in the frozen specimens showed that the degree of saturation in the surface layer was higher than that in the center of the specimen. The migration of pore water in the rock is possible during freezing if the freezing point of water is depressed by the small-pore sizes and other factors. The failure of the rock can start from an area with a higher degree of saturation.