Size effects on crystalline rock masses: Insights from grain-based DEM modeling

Abstract

This study aims to investigate size effects on the strength and cracking patterns of crystalline rocks with artificial flaws which are commonly used to represent rock masses. We used a grain-based model (GBM) in the discrete element method (DEM) to reproduce the mineral microstructure and performed uniaxial compression tests on geometrically-similar flawed rocks with specimen sizes varying from 0.5 to 3 times the laboratory standard specimen. The results show that GBM faithfully reproduces the strength and cracking processes observed in the experiments. The strength decreases and cracking patterns become less jagged as the sample size increases. The micro-mechanism for size effects is attributed to the increased likelihood of including more inter-grain cracking paths in larger specimens. Moreover, lower flaw inclination angles can increase these size effects. Because specimens with flatly-inclined flaws have a lower stress gradient on the flaw surface, resulting in a wider potential area for microcrack to initiate. This area can contain more options for inter-grain cracking paths in larger specimens, resulting in greater strength reduction. Hence, we observe more significant strength size effects. This research provides new insights into bridging the gap between experimental data obtained on the laboratory scale and their practical applications in field-scale scenarios.