Quantitative evaluation of shear wear on natural and fresh skarn joint surfaces based on acoustic emission and 3D laser scanning technology

Weathering substantially impacts the shear mechanical properties and surface morphology of rock joints. This study quantitatively compared shear behavior, shear strength parameters, acoustic emission (AE) characteristics, and surface wear of fresh and slightly weathered skarn joints under different constant normal load (CNL) conditions. The results indicated that weathering markedly degraded shear properties: the peak shear strength of weathered joints was only about 40% of that of fresh joints, and dilatancy behavior was absent during shearing of weathered joints. In contrast, fresh joints exhibited pronounced dilatancy, although this effect diminished with increasing normal stress. The AE signal response mechanisms of the two joint types were distinct. Analysis using the AE-based AF-RA (average frequency-rise time/amplitude) crack classification method (signal classification ratio k = 5) revealed that fresh joints showed a higher proportion of tensile cracks. In contrast, weathered joints exhibited a larger proportion of shear cracks. Frequency-band analysis revealed that fresh joints predominantly generated medium- to high-frequency signals, whereas weathered joints predominantly generated medium- to low-frequency signals. Quantitative three-dimensional (3D) laser-scanning analysis further demonstrated that the extent of surface wear was substantially greater on weathered joints than on fresh ones. Weathering-induced degradation of the mechanical and surface properties of rock joints has important implications for the support design in fractured rock masses and for the practical application of rock-mass classification systems such as the Q-system and the Rock Mass Rating (RMR).