Structural defects are inherent in almost every rock mass. In many cases, non-persistent cracks may coalesce into continuous fractures under dynamic loads, potentially affecting the stability of a rock structure. The study of the dynamic behavior of rock and concrete discontinuities has critical implications for civil engineering structures, the mining industry, and any other structures which may contain non-persistent cracks. In this paper, concrete Brazilian disks containing open, non-persistent joints were constructed and subjected to impact loading to investigate their impact energy behavior. The effect of some parameters, such as joint continuity factor (the relationship between joint length and rock bridge length), bridge angle, joint spacing, joint orientation, and impact angle were investigated physically to estimate the required energy for crack initiation. The results of experiments revealed that as the joint continuity factor increases, the required energy for crack initiation decreases. A minimum crack initiation energy exists for middling values of joint continuity factor, and there is evidence for interaction effects between this factor and joint spacing. Moreover, a relationship between bridge angle, loading direction and crack initiation energy was not found by the experimental study.


The rock mass is a natural geologic material that consists of intact rock and discontinuities at various scales, such as faults, weak bedding planes, fractures, and joints (Einstein et al. 1983; Yang et al. 2020). The existence of discontinuities, particularly joints, makes rock masses significantly different from other engineering materials and controls their deformation, strength, and dynamic responses (Kurtuluş et al.; Zhao et al. 2008; Che et al. 2016; Shang et al. 2016).The persistency of joints is known to have a significant impact on the mechanical behavior of rock mass subjected to static loads (Singh et al. 2002; Singh and Singh 2008). Non-persistent joints, which appear as a set of discontinuous joints, have been recently investigated in lab-scale samples under static loading conditions, with the uniaxial compressive and direct shear tests. (Fan et al. 2015; Asadizadeh et al. 2018a, 2019b; Cao et al. 2020; Guo et al. 2020). Non-persistent joints can be observed in large-scale rock masses, for example, around landslides, rock slopes, and failures of underground rock engineering sites. Since it is difficult to study in-situ crack coalescence behavior, many experiments have been conducted on real rock or rock-like specimens with pre-fabricated discontinuities (non-persistent and persistent joints), and some significant results have been obtained (Ghazvinian et al. 2012; Asadizadeh et al. 2018b).

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