Experimental investigation of plane shear fracture characteristics of sandstone after cyclic freeze–thaw treatments

Abstract

For jointed rock masses in cold regions, freeze–thaw cycles cause damage to the rock matrix and degradation of the strength parameters. To further understand the deterioration mechanism of freeze–thaw cycles, substantial efforts have been devoted to the investigation of the failure mechanism of rock after freeze–thaw treatments. Until now, little attention has been given to the degradation of fracture toughness and the change in the fracture surface morphology of rocks after cyclic freeze–thaw treatments, especially for planar shear fracture characteristics. In this research, experiments on double-notched sandstone specimens after different freeze–thaw cycles subjected to compression-shear tests were conducted to further investigate the effect of the freeze–thaw treatment on the mode II fracture toughness and fracture surface morphological characteristics. The results show that freeze–thaw cycles have an important role in the mode II fracture toughness and that the fracture toughness shows an obvious decreasing trend with an increase in freeze–thaw cycles (N). Moreover, the 3D surface topography was reconstructed by using 3D laser scanner scanning. Parameters such as fractal dimension, asperity height and slope angle show that the fracture surface becomes rougher with increasing N. In addition, based on the 2D contour lines extracted from fracture planes, the 3D joint roughness coefficient (JRC) values of 3D fracture surfaces were calculated. The results indicate that more freeze–thaw cycles will produce rougher fracture surfaces.