Abstract: The deterioration of rocks on reservoir bank slopes under flowing water conditions can seriously compromise slope stability. Meticulously exploring the macro-mechanical properties and microstructures of rocks under dynamic water scouring conditions is of great significance for disaster prevention and control in reservoir areas. To simulate the water flow environment of reservoir bank slopes, a rock scour resistance test device was designed. Taking sandstone as the research object, three conditions namely, natural drying, hydrostatic immersion, and hydrodynamic scouring, , were considered. Combining with laboratory test results, digital image correlation techniques, scanning electron microscopy, and fractal theory, the influences of different water environments on the mechanical properties of rocks were systematically explored in terms of macro-mechanical parameters, distribution characteristics of strain fields, and microstructure. The results indicate that the softening coefficients of compressive strength and elastic modulus of hydrodynamically scoured specimens decrease by 0.07 and 0.06 units, respectively, compared to those of water-saturated specimens. The inflection point of the strain field differentiation rate-axial strain curve appears before the peak stress, associated with the localization of the fracture process zone, serving as a precursor signal for rock fracture. Compared to the effect of hydrostatic immersion, the precursor point P of hydrodynamically scoured specimens appears earlier, as hydrodynamic scouring aggravates the development of internal defects, thereby facilitating the earlier appearance of the precursor point. Furthermore, the loss of mineral particles and cementing materials within the sandstone increases significantly after hydrodynamically scouring, leading to a more pronounced degradation of its microstructure than that of water-saturated specimens. This change is confirmed by the fractal dimension calculations of scanning electron microscope images, indicating that the hydrodynamically scoured specimens exhibit the largest fractal dimension.

Key words: scour, rock, digital image correlation method, mechanical properties, microstructure, fractal dimension