Investigation of excavation-induced brittle damage in hard rocks using large-scale true-triaxial experiments and 3D micromechanical DEM modeling
Final Report Abstract
Spalling is a common phenomenon in underground excavations, particularly in hard rock under high-stress conditions. Brittle failure typically begins with the development of microcracks near excavation boundaries. In this project, we investigated damage behavior around openings of various shapes using true triaxial tests and 3D discrete element method (DEM) modeling. Our findings reveal that crack initiation stress is influenced not only by the minimum principal stress but also by the intermediate principal stress and the shape of the opening—factors that remain underexplored and require further quantification. Due to the maximum load limitations of our testing apparatus, macro spalling was not observed in the experiments. However, both acoustic emission (AE) monitoring and numerical modeling consistently showed that damage tends to originate from locations with adverse stress conditions. These include the corners of square openings, the two bottom corners of D-shaped openings, and the roof and floor of circular openings. With the increase of applied loads, cracks would develop in side walls. Tensile cracks were found to dominate damage initiation in all tests. Damage progression was also inferred by monitoring velocity changes along paths passing through zones of interest. Numerical simulations highlighted the critical role of particle shape in accurately modeling damage development around openings. Triangular (2D) and tetrahedral (3D) particles proved to be superior for simulating excavation-induced spalling due to their ability to form smooth pathways for tensile crack propagation and shear fracture development. These particle shapes promote the localization and coalescence of microcracks to form macro spallings—features that are less pronounced in other models using circular or polyhedral particles. Additionally, AE signals were found to be highly sensitive to background noises, guiding us to improve our true triaxial testing device. Enhancements included optimizing AE sensor installation and reducing noise induced by loading mechanisms. This project has so far resulted in two published papers. We also plan to publish an additional paper focusing on the AE results in the near future.
Publications
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Effects of particle shape on mechanical responses of rock materials using bonded-particle model. Computers and Geotechnics, 176, 106754.
Bai, Qingsheng; Zhang, Cun & Konietzky, Heinz
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Experimental investigation of stress unloading effects on rock damage and confining pressure-dependent crack initiation stress of porous sandstone under true triaxial stress environments. Rock Mechanics Bulletin, 3(2), 100111.
Bai, Qingsheng; Friedel, Max & Konietzky, Heinz
