Study on the Damage Model of Non-Persistent Jointed Rock Mass under the Coupling of Freeze-Thaw and Shear.

Considering that a jointed rock mass in a cold area is often affected by periodic freeze-thaw cycles and shear failure, definitions for the mesoscopic and macroscopic damage to a jointed rock mass under the coupling of freeze-thaw and shear are proposed, and the damage mechanism is verified according to experimental results. The results show that: (1) the jointed rock specimens increase macro-joints and meso-defects, the mechanical properties deteriorate significantly under freeze-thaw cycles, and the damage degree becomes more and more significant with the increases in freeze-thaw cycles and joint persistency. (2) When the number of freeze-thaw cycles is constant, the total damage variable value gradually increases with the increase in joint persistency. The damage variable difference in specimens with different persistency is distinct, which is gradually reduced in the later cycles, indicating a weakening influence of persistency on the total damage variable. (3) The shear resistance of non-persistent jointed rock mass in a cold area is determined by the coupling effect of meso-damage and frost heaving macro-damage. The coupling damage variable can accurately describe the damage variation law of jointed rock mass under freeze-thaw cycles and shear load.

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 (Dw) and unevenness surface (Dr). These (microscopic) morphological parameters (S, Dw and Dr) 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 Dw and Dr. On the other hand, with the increase of the freeze-thaw cycle (N), Dw increases while Dr reaches the maximum at an early stage of the cycle, where Dr > Dw. 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 Dr, and then it is controlled by the waviness surface Dw during the freeze-thaw cycle.