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

Abstract

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.