Abstract

Rock masses in underground engineering projects, such as roadways or pillars, are inevitably subjected to cyclic dynamic loading, and the damage behaviour of jointed rock masses is often influenced by the different characteristics of the preexisting rock damage. To investigate the effect of cyclic impact on the fracture characteristics of rocks, fracture tests were conducted using SCC (short core in compression) specimens with dissimilar impact damage. The experimental results showed that cyclic impact led to mesoscale fracture and strength deterioration in rock specimens. As the number of impacts increased, the dynamic peak stress of marble decreased, and the maximum strain and the energy absorbed by marble increased. At the same time, cyclic impacts generated continuous damage to the interior of the specimen, and the white spot inside the specimen with higher impact times was more obvious. Based on the fracture test results, the mode II fracture toughness was calculated, and it decreased by 6.9, 20.9, 43.3, 66.8, and 87.0% for specimens that underwent 1–5 cyclic impacts, respectively. After fracture, the three-dimensional topography characteristics of the fracture surface were obtained by a 3D optical scanner. Overall, the fracture surface became increasingly tortuous with increasing impact number. For the fractal factor D, the variation in the mean squared deviation of the asperity height and slope angle exhibited an increasing tendency with an increasing number of impacts.

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