Study of mode II fracture characteristics and roughness in salt rock after treatment coupled thermo-hydro-mechanical environment

Abstract

It is crucial to observe the fracture characteristics and roughness of rocks subjected to thermo-hydro-mechanical (THM) coupling experiments. Previous studies have predominantly focused on investigating fracture characteristics in mode I, with comparatively less attention given to mode II fractures of rocks, especially following combined THM treatment. Therefore, this study focuses on utilizing salt rock as the primary subject, and the specimens are pretreated using a self-designed THM coupling triaxial tester. Subsequently, the three-point bending (SCB) test is conducted under ambient pressure conditions. At the peak load stage, the length of the fracture process zone is determined using the digital image correlation (DIC) technique. Additionally, macroscopic and microscopic fracture information on the fracture surface is recorded using 3D laser scanning and electron microscopy. Fracture roughness is evaluated using the apparent tilt function. The findings indicate that: 1) When subjected to various THM coupling conditions, the fracture toughness of salt rock in mode II exhibits a similar evolutionary pattern to that of mode I. However, its value experiences a rapid decrease once the temperature exceeds 500 °C. 2) With increasing temperature, the number of microcracks in salt rock and the degree of microdamage both escalate, leading to a progressive extension of the fracture process zone at the crack tip during the peak stage. 3) Gradually increasing temperature causes a progressive rise in the fracture roughness of salt rock. This is evident in the fact that the roughness along the crack propagation direction is less than that perpendicular to the crack propagation direction. The anisotropy of fracture roughness diminishes gradually.