Multiscale investigation of localized deformation around boreholes and galleries in heterogeneous and anisotropic rocks

Context: The PhD project aims to improve the understanding of initiation and evolution of failure by localized deformation around underground excavations in heterogeneous and anisotropic porous rocks, a key issue for the stability and integrity of deep boreholes and galleries in the context of the energy transition. Deep excavations in natural formations induce complex three-dimensional stress redistributions, and the resulting strain localization patterns depend strongly on multi-axial loading paths, as well as on natural rock anisotropy and heterogeneity. Despite their importance for engineering applications, these in-situ conditions remain insufficiently represented in existing laboratory datasets and are only partially accounted for in current modelling approaches.

This PhD research will investigate, through combined advanced experimental and numerical approaches, the mechanisms of localized deformation around boreholes and galleries in heterogeneous and anisotropic sedimentary rocks, under true triaxial stress paths representative of in-situ conditions.

Numerically, the study will first benchmark classical elasto-plastic FEM models against the experimental results and assess the performance of classical constitutive laws in capturing the rock response during cavity depressurization under multi-axial loading. A second, multi-scale component will employ a hierarchical FEM×DEM framework that incorporates grain-scale mechanisms (cohesion loss, grain breakage, granular network rearrangement) and controlled heterogeneity distributions. The numerical study will provide new insights into the capabilities for advanced multi-scale models to capture the mechanisms governing damage development around deep excavations and support the development of predictive models, capable of accounting for realistic stress paths and microstructural complexity.