Abstract: To explore the accelerated disintegration mechanism of Gansu red-bed clay-bearing rock under drying-wetting cyclic, water immersion test and slake durability test were carried out. The main factors affecting rock durability were analyzed by comparing clay-sulfate rock with argillaceous sandstone, shale, and gypsum rock. Furthermore, the mineral inclusion effect during the disintegration process was discussed. The results of the experiment show that the natural disintegration rate of undisturbed clay-sulfate rock is relatively slow, and the disintegration rate of the sample is 0.11 after soaking for 3 h. After drying at a high temperature (163 ℃), the mixed gypsum minerals will be dehydrated with the volume shrinkage, and the rock mass will completely disintegrate within 2 hours when it is soaked in the water again. The clay-sulfate rock belongs to highly durable rock and its slake durability index of the second cycle I_d2 is 0.80. However, an accelerated trend can be observed in the disintegration, and the relative slake durability index of the fifth cycle I₅ is up to 0.56. The durability of rock is greatly affected by the mineral composition and cementation strength. In the process of rock disintegration driven by mineral expansion, argillaceous blocks are prone to uniform crushing, while sandy blocks are prone to uneven crushing. Because the clay minerals inclusion is dense, disintegrating of the clay-sulfate rock is intensive. The sulfate mineral inclusion is corrosive, and its solution shows weak acidic. Therefore, the main reasons for the accelerated disintegration of clay-sulfate rock are micro-cracks produced by gypsum corrosion and the abscission of calcareous nodules in the acidic environment.

Key words: red-bed clay rock, disintegration, sulfate inclusion, expansive mineral, corrosion