Impact of Holes and Single Notch on Acoustic Emission Variations and Mechanical Characteristics of Notched Specimens at Axial Loading

Fractures and imperfections, like holes and joints, often occur in rock masses. These defects have a larger impact on the performance of rock engineering structures when the strength of the rock matrix is high. Geometric breaks interacting with each other can cause rock structure failures. Strength and failure behavior of rock samples in different kinds of flaws are useful for characterizing failure modes and load-carrying capacity in underground and surface rock engineering activity, such as modes of failure and load capacity. The majority of the previous work has generally been concerned with laboratory specimens with artificially induced flaws under uniform simulated rock or intact rock loading. Some of these examples are gypsum (Haeri et al. 2015a), cement mortar (Haeri et al., 2014a, 2014b; Haeri & Sarfarazi, 2019), concrete (Zhou et al., 2023a, 2023b), granite (Amini et al., 2023), asphalt (Wang et al., 2023), and coal (Fu et al., 2022). In an experiment series, Haeri (2015), Haeri et al. (2015a, 2015b) cast concrete specimens with three holes to observe the influence of the shape of the hole on mechanical performance and failure behavior. They concluded that radial cracks initiated at the outer edges of the holes due to high hoop stress, and ultimate failure occurred as these cracks interacted and merged. Even though the influence of holes on the mechanical behavior of rock and other similar materials has been studied before, there has not been any work to examine the roles of holes and a single notch together. In addition, its ramifications for global failure mechanisms are not addressed. The current study aims to investigate the effects of joint opening, crack-filling materials, and flaw orientation (the relative position of flaws regarding the applied load) on rock mass failure mechanisms. Towards this end, gypsum samples with multiple holes and a priori notch were subjected to uniaxial compressive loading, where the emphasis was laid on crack growth and coalescence. Complementary numerical calculations were performed using PFC2D, and these were compared against the experiment.