Abstract
Major civil and military infrastructures are usually located in mountainous areas with complex geological structures. When subjected to impact loads caused by operational blasting or seismic activities, the inherent flaws or joints in the hosting rock mass may grow irreversibly and eventually and cause the entire structure to collapse. It is, therefore, desirable to understand the mechanical and cracking behaviors of flawed rock structures under dynamic loads. In this work, the cement mortar is used to make the plate specimens, and two different types of flaws, i.e., the open and the closed (resin-filled) flaws, with different inclination angles from 0° to 90° with respect to the loading direction are prefabricated. The nominal strength, crack initiation, and failure characteristics of the specimens under different loading rates are investigated using the split Hopkinson bar (SHPB) system in conjunction with the digital image correlation (DIC) technique. The results indicate that the dynamic nominal strength of both two types of specimens shows similar loading rate and flaw angle dependency, specifically, monotonically increasing with the increase of the loading rate while increasing first and then decreasing with increasing the flaw inclination angle. The strength of specimens with an open flaw is obviously lower than that of the specimens with a closed flaw at a similar loading rate. Besides, the failure mode of specimens with an open flaw is mainly an X-shaped tensile or tensile-shear mixed form regardless of the flaw inclination, whereas the resin-filled flawed specimens always fail in the form of an atypical X-shaped shear pattern with obvious randomness. Moreover, the stress field around the crack tip is carefully extracted based on the obtained displacement field from DIC analysis; the stress intensity factors at crack initiation onset also show flaw inclination- and loading rate-dependent behavior. The strength, cracking behavior, and stress field around the tip during the dynamic loading are closely related to the friction effect between the flaw surfaces. The findings in this work provide some basic insights into the cracking mechanism of rock with open and closed flaws under dynamic loading conditions.
Highlights
IntroductionRock masses are generally discontinuous at various scales due to the presence of faults, joints, fissures, partings, flaws, and any other inherent defects formed during the diagenesis process and geological-tectonic evolution [1–3]
Considering the flaw in practical rock engineering is often infilled, some efforts have been devoted to studying the effect of the closed flaws on the fracturing process [9, 19, 23–25]. eir results demonstrate that the cracking behaviors are obviously different between closed and open flaws, and the overall strength, initiation, and coalescence stresses for closed flaws are higher than those of the open flaws due to the friction effect and the stress transmission capacity
E effects of the flaw inclination angle, loading rate, and infilling conditions are carefully considered, and the stress intensity factors are obtained in accordance with the digital image correlation (DIC) results. e conclusions are summarized as follows: (1) e dynamic nominal strength of both two types of specimens shows similar loading rate and flaw angle dependency, almost linearly increasing with the increase of the loading rate, whereas increasing first and decreasing with the inclination angle
Summary
Rock masses are generally discontinuous at various scales due to the presence of faults, joints, fissures, partings, flaws, and any other inherent defects formed during the diagenesis process and geological-tectonic evolution [1–3]. The overall compressive strength of the flawed rock is significantly lower than that of the intact rock at similar loading conditions [5], and the flaw inclination angle can significantly affect the crack initiation position, propagation angles, and even the propagation priority [21]. Considering the flaw in practical rock engineering is often infilled, some efforts have been devoted to studying the effect of the closed flaws on the fracturing process [9, 19, 23–25]. Eir results demonstrate that the cracking behaviors are obviously different between closed and open flaws, and the overall strength, initiation, and coalescence stresses for closed flaws are higher than those of the open flaws due to the friction effect and the stress transmission capacity Considering the flaw in practical rock engineering is often infilled, some efforts have been devoted to studying the effect of the closed flaws on the fracturing process [9, 19, 23–25]. eir results demonstrate that the cracking behaviors are obviously different between closed and open flaws, and the overall strength, initiation, and coalescence stresses for closed flaws are higher than those of the open flaws due to the friction effect and the stress transmission capacity
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