MECHANISMS OF ROCK BREAKDOWN BY FROST ACTION - AN EXPERIMENTAL APPROACH

Freezing behavior and frost shattering of rocks were studied in the laboratory. Rates of frost shattering were determined for 47 different samples of saturated rocks partially immersed in water by a decreasing rate of the longitudinal wave velocity during freeze-thaw cycles. The ratio of surface area per unit volume to tensile strength gives a good estimation of the frost shattering rate. This indicates that water migration caused by adsorptive suction participates in the frost shattering, as well as the 9% volumetric expansion. Frost shattering occurred in porous rocks despite the lower saturation level than the theoretical value derived from the volumetric expansion theory. Furthermore, the open system was much more effective in frost shattering than the closed system was. Such moisture effects also demonstrate the large role of water migration in frost shattering. The linear strain of some saturated rocks during a freeze-thaw cycle was measured with foil strain gauges. Immersion in water increased the freezing expansion of tuffs, although it affected the strain of a shale and an andesite only little. Low cooling rates resulted in small freezing expansion of rocks placed under the closed system because of creep of pore ice. These results suggest that the freezing expansion of a rock consists of three components: two positive strains due to the 9% volumetric expansion of water, and water migration controlled by adsorptive suction, and a negative strain due to creep of ice. The frost shattering of the tuffs would be primarily controlled by the water migration, and that of the shale and andesite is probably caused by the volumetric expansion. The relative contribution of the two processes on frost shattering may depend on the surface area per unit volume of the rocks. © 1990 Elsevier Science Publishers B.V. All rights reserved.