A modified three-dimensional rigid-body-spring method for mechanical behavior of transversely isotropic rocks

A novel anisotropic discrete approach framework is developed to simulate the mechanical behavior of transversely isotropic rocks. This framework is based on the three-dimensional modified Rigid-Body-Spring Method (3D mRBSM) integrated with three key anisotropy ingredients: (1) an anisotropic block geometry method based on spatial transformation to generate blocks with controlled aspect ratios; (2) an anisotropic spring parameter assignment using a cubic Bézier curve to capture directional variability in elastic properties and failure strength; and (3) a directional spring-set model (DSM) to incorporate microscopic structural weaknesses. A comprehensive parametric study is conducted to evaluate impacts of each direction-related parameter on Young's modulus, strength and failure patterns. The results indicate that the combined use of the three anisotropy ingredients enables the model to exhibit flexible anisotropic mechanical behavior, and further highlights the critical role of anisotropic block geometry in governing such behavior. The model is validated by investigating the anisotropic mechanical response of Callovo-Oxfordian claystone and Tournemire shale. The comparisons between numerical predictions and experimental data demonstrate that the proposed 3D mRBSM framework effectively reproduces the main features of experimentally observed mechanical behaviors and it provides a robust and scalable approach for modeling the mechanical properties of transversely isotropic rocks.