Temperature-Induced Deterioration Mechanisms in Mudstone during Dry–Wet Cycles

Although temperature is a main external effect on rock decay, the relationship between a rock’s decay rate and temperature still remains unclear and there is limited information about the rate of rock decay under varied temperatures during dry–wet cycle conditions in southwest China. Therefore, the aim of the present paper was to explore the rate of mudstone decay through an experiment, in which a model was proposed to calculate their decay rates under varied temperatures conditions. A set of customized test device, including a model test container, a thermostat-controlled heating plate, and a water supply and drainage device, was applied in the experiment. Three dry–wet cycles were conducted on five samples at 60, 90, 105, 120 and 180 °C, respectively. The crack width, vertical displacement and wetted area were measured to analyse the temperature-induced decay mechanism during dry–wet cycle processes. The results showed that tiny cracks appeared on the surface of samples after heating and that the vertical displacement increased in the upward direction due to swelling of the mudstone after water exposure. The crack width extended with increasing water exposure, but it decreased after the surface of samples was gradually wetted after several hours of water exposure. The continually increasing wetted area and progressively fast wetting speed were the outward manifestation of the increasing number of internal cracks. Temperature-induced stress could promote the generation of cracks and decay rates of the tested rocks raised with higher temperatures. Quantitative analysis revealed that the rock decay rate is significantly related to temperature in the form of a S-Curve. The sample barely decayed at 60 °C, but the decay rate was close to 90% at 180 °C. The higher the temperature was, the faster the wetting speed was and the more cracks generated, and ultimately rocks decayed as a result of crack extension.