Effects of particle shape on mechanical responses of rock materials using bonded-particle model

Abstract

This study examines the impact of particle shape (ball, polygon, and trigon) on rock mechanical behavior using laboratory-scale tests and a field experiment with the soft bond model (SBM). Parametric analysis shows that the softening behavior in SBM significantly influences the strength ratio (R_ct) between uniaxial compressive and tensile strength, but depending on bond strength ratio (R_bs), softening factor (ζ), and particle shape. By adjusting these parameters, we achieve an R_ct ranging from 8 to 80, suitable for most rock materials. Adjusting micro-parameters such as friction angle and coefficient allows us to obtain failure envelope slopes ranging from 30 to 60 degrees. Compared to the ball particle model (BPM) and trilateral particle model (TPM), the polygonal particle model (PPM) is more sensitive to friction coefficient due to enhanced interlocking mechanisms near macro shear bands. While all three models effectively replicate laboratory experiments on hard rocks, the PPM tends to exhibit unrealistically high dilation before peak stress, and BPM and PPM fail to capture non-linear failure envelopes at high confinement. Overall, TPM with SBM overcomes common shortcomings observed in traditional particle bond models. Simulations of the Mine-by tunnel demonstrate that TPM successfully reproduces the notch profile and the spalling mechanism, whereas both BPM and PPM cannot replicate the spalling. Detailed analysis reveals that TPM facilitates the creation of smooth pathways for tensile cracks and propagation of shear fractures, promoting the localization and coalescence of microcracks − features absent in the other two models.