Phase field modelling of tunnel excavation damage in transversely isotropic rocks

Abstract

Layered rocks, prevalent in geological formations, exhibit complex failure behaviours driven by pronounced anisotropy in their mechanical properties. However, the intricate failure mechanisms remain inadequately understood due to the spatial complexity of these mechanical responses. To address this challenge, this study proposes a novel phase field model tailored for layered rocks. A new strain energy decomposition method is introduced, uniquely formulated based on stress components and designed for transversely isotropic constitutive models. Numerical solutions to the coupled stress-phase field equations are obtained using user-defined element and material subroutines, implemented through a staggered solution scheme. The accuracy and robustness of the numerical approach are validated through simulations of a composite panel with a central hole under tensile loading. Additionally, the model is applied to the excavation of the layered soft rock tunnel, revealing the significant influence of bedding plane angles on displacement and stress field distributions, as well as post-excavation failure modes. Notably, the model captures the predominant shear-slip failure along bedding planes following excavation, effectively reflecting the complex mechanical interactions in layered rocks. This proposed model represents a significant advancement in understanding the failure mechanisms of layered rocks, providing a valuable tool for future geotechnical applications.