Mechanical degradation and particle breakage of sandstone rockfill material under wetting-drying cycles

Wetting-drying cycle is a significant factor contributing to the deterioration of dam rockfills, leading to increased settlement and weakened stability of dams. Despite its importance, the impact of the wetting-drying cycle on the mechanical and particle breakage characteristics of continuously graded rockfill aggregates under a triaxial stress state remains unclear. This study conducted a series of large-scale triaxial drainage shear tests on sandstone rockfill materials from the Lianghekou rockfill dam in China under different wetting-drying cycle conditions. The results revealed that increased confining pressure exacerbates the wetting-drying degradation of peak strength and modulus. The wetting-drying cycle induced changes in drainage volume, with an increase during consolidation and a decrease during shear, alongside a notable rise in particle breakage and the proportion of grain groups below 0.5 mm. Subsequently, a hyperbolic crushing model considering wetting-drying cycle and plastic input work was proposed. Moreover, X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests exhibit significant changes in mineral content and micromorphology. Finally, the discussion addressed how the mechanisms of the wetting-drying cycle impact the crushing degree and strength of samples. Four dominant deterioration mechanisms of the rockfill particles during wetting-drying cycle were revealed: mineral dissolution/flushed away, expansion pressure in microcracks induced by water-absorbing of clay minerals, crystallization pressure in microcracks after water loss of insoluble salts, the adsorption effect of clay minerals and stress due to inhomogeneous deformation between water-soaked regions and dry regions.