Abstract: A series of water vapor cycle experiments was conducted to examine the evolution of strength, deformation, and damage characteristics of red mudstone. The experiments included uniaxial compression tests and Brazilian splitting tests, utilizing acoustic emission (AE) and three-dimensional digital image correlation (DIC-3D) technology. The study concentrated on the evolutions in strength, deformation, and damage characteristics of red mudstone following different water vapor cycles. Results indicated that as water vapor cycles increased, the water content and volume of the mudstone showed irreversible accumulation, and the time required to reach water vapor equilibrium extended. Water vapor cycles caused reductions in compressive strength, tensile strength, elastic modulus, and shear modulus of the mudstone, leading to the proposal of an exponential degradation model for red mudstone. During uniaxial loading after different water vapor cycles, the failure mode of mudstone transitioned from overall shear failure to localized development of dispersed cracks. The evolution characteristics included delayed closure points of fractures, earlier onset of initial and damage stresses, extended compaction processes, shortened linear elastic deformation stages, and reduced ability of the rock to resist deformation.

Key words: red mudstone, water vapor cycle experiments, DIC-3D technology, acoustic emission technology