Since its development, the grain-based model (GBM) has been demonstrated to be capable to capture the strength and deformation behavior and the micro-cracking process under different loading conditions. In the GBM, individual grains resemble the actual constituent minerals, while each grain comprises multiple bonded particles. Particle size is an important micro-parameter of bonded particle model used in the particle flow code (PFC) for studying the rock mechanical behavior. However, most of the previous studies simply select the particle size based on the consideration of computer capacity and efficiency, without comprehensively accounting for its effect on the simulation results. This paper numerically investigates the effect of grain size to particle size ratio on the simulation results using GBM. Numerical PFC specimen models with different grain sizes and particle sizes are first generated, on which numerical simulations of uniaxial compression test are then conducted.
The results in this study show that both grain size and particle size have a significant influence on the strength and deformation parameters and the induced micro-cracking process. By correlating the simulated uniaxial compressive strength and Young's modulus with the grain size to particle size ratio, it is found that the two parameters increase with the grain size to particle size ratio, and their increase gradually diminishes when such ratio reaches a threshold. Due to such remarkable influences on numerical results, these two geometrical parameters should be properly determined during the parameter calibration stage.
A good understanding of the rock strength and deformation will facilitate cost-effective design and long-term stability maintenance of engineering structures constructed in or on rocks. Numerous laboratory test results have revealed that the deformation (failure) of rocks is mainly controlled by its inherent microstructure and the associated micro-cracking process (Brace et al., 1966; Bieniawski, 1967). The microstructures are usually associated with the different mineral aggregations and varying amounts of micro-defects such as micro-cracks, voids, and cleavage planes (Kranz, 1983). It is, therefore, of vital importance to comprehensively study the influence of inherent microstructures on the failure behavior and the induced micro-cracking process of rocks.
