Quantitative study of unlocking mechanisms of rock mass containing a locking section: insights from DIC and IR techniques

To study the unlocking mechanisms of the rock mass containing a locking section, sandstone specimens with two edge flaws are prepared and subjected to uniaxial compression tests, considering flaw inclinations of 30°, 45°, and 60°. The whole failure process of these specimens is monitored by the digital image correlation (DIC) method and infrared radiation (IR) technique. The flaw inclination exerts a substantial influence on the mechanical properties and failure pattern. The step-path failure is found in the case of α = 30°, while the retaining-wall failure is observed in the case of α = 45° and 60°. The relative displacement extraction, extended from the DIC, is applied to identify and quantitatively analyze the cracking behavior. Based on the relative displacement across the flaw, the locking effect is found to be weaker in the specimens with α = 30° than in those with α = 45° and 60°. According to the relative displacement within the locking section, two unlocking modes are identified: slow unlocking, characterized by a stable development in the relative displacement, and rapid unlocking, characterized by a stable and then exponential change in the relative displacement. By the IR monitoring, the thermal anomaly points are uniformly distributed in the specimens with α = 30° but progressively concentrated toward the failure planes in the specimens with α = 45° and 60°. The spatiotemporal characteristics of IR temperature fields are quantified by the discrete statistical method and the novel spatial distribution statistical method, standard deviational ellipse (SDE). The quantitative indicators, including standard deviation, skewness, and SDE parameters, exhibit stable development in the specimens with α = 30° but pronounced stagewise development and significant variability in the specimens with α = 45° and 60°.