Influence of water content on the failure modes and macro-micromechanical properties of sulfate rocks: Insights from experimental and DEM simulations

• Proposed and validated a novel 3DEC-GBM modeling framework and method. • Revealed the fundamental mechanisms governing the evolution of mechanical properties and failure modes of clay-sulfate rock under different initial water contents. • Developed a predictive model for mechanical properties that explicitly integrates initial water content effects. The initial water content significantly affects rock mechanics, especially with swelling minerals. However, the effects of initial water content on the mechanical properties and failure mode of sulfate rocks remain unclear. This study explores these effects by conducting unconfined compressive strength (UCS) experiments and discrete element method simulations on sulfate rocks. The results indicate that as the initial water content increased from 0 to 9%, the Young’s modulus and Poisson’s ratio of sulfate rock exponentially decreased by 48.9% and 290%, respectively. Additionally, the crack initiation stress ( σ c i ), crack damage stress ( σ c d ), and UCS decreased by 62.4%, 51.5%, and 53.3%, respectively. The stress responses to initial water content follow linear functions. Notable decreases were also observed in the normal and shear stiffness parameters ( k n and k s ) of contact, diminishing by 46.53% and 46.54%, respectively; peak cohesion decreased by 69.70%; peak friction angle by 17.39%; peak tensile strength by 124%. Rising initial water content leads to increased damage and softening of sulfate rock, causing decreased mechanical properties. It can be observed that as the initial water content increases, the proportion of micro-tensile fractures in the total number of fractures increases, and the dominant failure mode of sulfate rock gradually transitions from shear to tensile failure.