Mechanical properties and damage constitutive model of tuff under stress–seepage coupling during low-temperature curing

Given the challenging conditions of high-alpine and high-altitude metal mining, complex factors affecting rock mass quality, and the intricate mechanisms of slope instability, this study focuses on the tuff from the high-alpine and high-altitude region of China. The deformation, strength, and failure characteristics of the tuff specimen were investigated through uniaxial compression tests, stress–seepage coupling triaxial compression tests under low-temperature curing conditions and nuclear magnetic resonance analysis. A damage constitutive model for the tuff specimen considering curing temperature was established. Results show that low temperatures significantly promote the development and interconnection of pores and fissures within the tuff specimen. Low-temperature and stress–seepage coupling increase the number of pores and fissures and drive their growth toward larger sizes. The tuff specimen undergoes compaction, elastic deformation, plastic yielding, and failure under triaxial compression. As temperature decreases, failure transitions from simple shear to combined shear-tensile failure, with extended compaction and shortened plastic yielding phases, leading to enhanced brittleness. A low temperature–load coupling damage variable was introduced based on nuclear magnetic resonance porosity and the Weibull distribution function, effectively modeling the stress–strain relationship and strength characteristics of the tuff specimen under low-temperature and stress–seepage coupling, with a good fit between experimental and theoretical.