Abstract: Red mudstone, a common soft rock, is widely distributed in southwest, northwest, central and southern China. As the mechanical properties of red mudstone degrades remarkably under the action of water, engineering accidents inclusive of collapses and landslides occur frequently in red mudstone area under the influence of rainfall. A simple test apparatus and test scheme was designed in the present research to investigate the deformation and strength features of red mudstone under the combined action of loading and hydration. The holistic process of red mudstone encountering sudden rainfall after extreme drought undergone dry state and saturation under different load levels were simulated. The conclusions are presented as follows: (1) the uniaxial compressive strength of water-saturated red mudstone was considerably lower than that of dry red mudstone, implying an evident hydration effect; while the stress level failure of dry red mudstone under the action of water lagged far behind the strength of saturated red mudstone. (2) Despite that the deformation of rock specimen experienced a progressive process from gentle development to dramatic surge under a certain stress level, the failure of specimen happened abruptly and instantly, and after failure, the specimen was in a muddy state.

Key words: red mudstone, deformation characteristics, water-rock interaction, load, softening coefficient, brittle failure