Evolution of Shear Surface Morphology of Jointed Rock Masses Based on Gaussian Filtering Method under Freeze-Thaw Cycles

This study aims to quantify the shear surface morphology of jointed rock and its evolution under shearing, cyclic freezing, and thawing using the Gaussian filtering method. Gaussian filtering method enables the construction of the (large-scale) waviness surface and the (small-scale) unevenness surface of a digitized surface (created by laser scanning). Both waviness and unevenness surfaces are then quantified by roughness coefficient ratio (S) and degradation degrees of the waviness surface (D(w)) and unevenness surface (D(r)). These (microscopic) morphological parameters (S, D(w) and D(r)) are subsequently used to explain the development of the (macroscopic) shear strength of the jointed rocks on direct shear tests. The results indicate that compared with fresh jointed rocks, the freezing and thawing causes the potential shear surface asperities to be easier to damage and fail under shear load. Such damage is well represented by the significant decrease in D(w) and D(r). On the other hand, with the increase of the freeze-thaw cycle (N), D(w) increases while D(r) reaches the maximum at an early stage of the cycle, where D(r) > D(w). This difference reveals the underlying shear mechanism microscopically; that is, in the initial stage, the shear surface morphology is mainly dominated by the unevenness surface D(r), and then it is controlled by the waviness surface D(w) during the freeze-thaw cycle.