Macro- and micromechanical properties of flawed sandstone and their degradation mechanisms under hydrodynamic scouring

Abstract

To reveal the degradation mechanisms of the mechanical properties of a rock mass in a reservoir bank slope under hydrodynamic scouring, a hydrodynamic scour test device was developed in this study. Sandstone specimens containing prefabricated flaws were used as the research objects. Three conditions, namely, natural conditions, hydrostatic immersion, and hydrodynamic scouring, were considered. By considering the results of laboratory testing, digital image correlation (DIC), scanning electron microscopy (SEM), and thermodynamic analysis and fractal theory, the effects of different flow states on the mechanical properties of the flawed rock mass were systematically investigated in terms of the macromechanical parameters, strain field, strain energy, and microstructure. A crack initiation stress identification method based on the differentiation rate of the effective variance of strain fields was proposed. The energy conversion in the rock loading process was quantitatively characterized using three strain energy characteristic indicators. The internal microstructure of the rock was quantitatively characterized using a combination of SEM image characteristics and the fractal dimension. It was found that the uniaxial compressive strength, elastic modulus, crack initiation stress, energy storage limit, elastic strain energy conversion rate, and dissipated strain energy conversion rate of the hydrodynamically scoured specimen were the smallest, while the fractal dimension was the largest. There was a strong correlation among the mechanical parameters, energy characteristic indicators, and fractal dimensions of differently treated sandstone specimens because the macromechanical response and energy conversion characteristics of a rock mass are closely correlated with changes in its internal structure.