Time-Dependent Fracturing in Granite Under Uniaxial Compression

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ABSTRACT: Time-dependent processes in rock govern its long-term behavior; hence, understanding these processes is very important, especially for long-lasting surface and underground structures. A series of laboratory-based uniaxial compression tests coupled with acoustic emission (AE) monitoring was conducted to explore the influence of control mode and loading rate on AE characteristics and the damage processes of granite. The experiments were carried out under axial displacement controlled and load controlled modes at varying displacement and loading rates. The stress-strain behavior, strength, AE characteristics, and failure modes were analyzed. The loading and displacement rate in the two control modes significantly affected the mechanical properties of the rock specimen. Results indicated a decrease in rock strength by 15% when the displacement rate reduced from 1μm/s to 0.05 μm/s, and in load-controlled mode, the strength reduced by 20% as the loading rate decreased from 0.55 kN/s to 0.02 kN/s. With the increase in the loading and displacement rates, a noticeable decrease in the time of failure was observed. Acoustic emission (AE) results showed that initially, the loading rates had minimal effect on the damage source parameters, whereas during crack propagation, their influence became substantial. Explosive or tensile events were obtained as the dominant failure mechanism. Under a high displacement rate, the proportion of the explosive events was higher; as the displacement rate reduced, the proportion of the explosive events reduced, and shear events increased. Load-controlled experiments showed insignificant variation in the proportions of the different fracturing mechanisms by changing the loading rate. Decreasing b-value indicated the evolution of large-magnitude events under high rates of loading. This study offers fundamental insights into how brittle rocks undergo damage evolution under various loading and displacement rates, whether in load-controlled or displacement-controlled conditions. 1. INTRODUCTION Understanding the mechanisms of microcracking in rocks over time is crucial for assessing the long-term stability of various rock engineering structures, including tunnels, mining chambers, rock slopes, and nuclear waste repositories. This understanding is essential for evaluating the long-term stability of rock engineering structures such as tunnels, mining rooms and pillars, rock slopes, and nuclear waste repositories (Diederichs and Kaiser 1999, Nara et al. 2010, Paraskevopoulou et al. 2018, Zhang et al. 2020, and Zhao et al. 2022). Furthermore, time-dependent factors also significantly influence the exploration and utilization of resources such as oil and gas reservoirs and enhanced geothermal systems (EGS), as noted by Demarest (1976) and Cornet (2007).