Dynamic Mode II Fracture Characteristics and Shear Surface Morphology of Granite Under Triaxial Confining Pressure.

Shear fracture is a significant failure mechanism in particular disaster such as fault slips and rockbursts in deep rock engineering, which frequently involve in-situ stress and disturbance loads from earthquakes or blasting. Studying the dynamic shear fracture behavior of rocks under confining pressure is crucial for disaster prevention. This study performed a series of dynamic mode II fracture tests under different confining pressures using granite short core in compression (SCC) specimens via a modified triaxial split Hopkinson pressure bar (SHPB) system. It is discovered that (1) dynamic mode II fracture toughness increases as loading rate and confining pressure rise; (2) The Linear relationship between dynamic or static fracture toughness and confining pressure is independent of loading rate. An empirical equation was presented to quantify relationship between fracture toughness, confining pressure and loading rate. The final failure degree of SCC specimens aggravates as the loading rate increases or confining pressures reduce. The morphological features of fracture surfaces were quantitatively investigated using fractal and statistical theories. It was observed that roughness in dynamic fracture surfaces decreases with increased in confining pressures and loading rates. Statistical analyses on asperity height <italic>h</italic> and slope angle<italic> α</italic> indicate that the undulation of fracture surfaces decreases with confining pressure at a given loading rate, validating the fractal results. A new index, namely the number of dominant intervals (NDI), is proposed to quantify the degree of aspect orientation distribution concentration. Generally, there is a notable trend of reducing NDI with confining pressures and loading rates. [ABSTRACT FROM AUTHOR]