Quantifying the Rock Damage Intensity Controlled by Mineral Compositions: Insights from Fractal Analyses

Since each rock type represents different deformation characteristics, prediction of the
damage beforehand is one of the most fundamental problems of industrial activities and rock
engineering studies. Previous studies have predicted the stress–strain behaviors preceding rock
failure; however, quantitative analyses of the progressive damage in different rocks under stress have
not been accurately presented. This study aims to quantify pre-failure rock damage by investigating
the stress-induced microscale cracking process in three different rock types, including diabase,
ignimbrite, and marble, representing strong, medium-hard, and weak rock types, respectively. We
demonstrate crack intensity at critical stress levels where cracking initiates (ci), propagates (cd),
and where failure occurs (peak) based on scanning electron microscope (SEM) images. Furthermore,
the progression of rock damage was quantified for each rock type through the fractal analyses of
crack patterns on these images. Our results show that the patterns in diabase have the highest fractal
dimensions (DB) for all three stress levels. While marble produces the lowest DB value up to ci
stress level, it presents greater DB values than those of ignimbrite, starting from the cd level. This is
because rock damage in ignimbrite is controlled by the groundmass, proceeding from such stress
level. Rock texture controls the rock stiffness and, hence, the DB values of cracking. The mineral
composition is effective on the rock strength, but the textural pattern of the minerals has a first-order
control on the rock deformation behavior. Overall, our results provide a better understanding of
progressive damage in different rock types, which is crucial in the design of engineering structures.