Nonlinear evolution of granite pore-fracture networks and critical temperature for accelerated transition under coupled THM treatment
DOI:
https://doi.org/10.62813/see.2025.01.06Keywords:
Coupled THM experiment, Granite, Pore and fracture structure, Excavation damaged zone , Fractal dimensionAbstract
To systematically elucidate the nonlinear evolution of granite pore-fracture networks and identify the critical temperature for accelerated transition under thermo-hydro-mechanical (THM) coupling treatment, representative Beishan granite samples were tested. A self-developed triaxial apparatus was employed to replicate in-situ conditions by applying confining stress (40 MPa), seepage pressure (0.6 MPa), and temperatures (25-200°C). Micro-computed tomography (MCT) scanning combined with image processing (noise reduction, segmentation, and 3D reconstruction) enabled detailed microstructural analyses. Fractal theory analysis and pore network modeling (PNM) were further adopted to quantify porosity, connected porosity, fractal dimension, pore-size distribution, and pore-fracture network topology. Results show that THM coupling significantly accelerates damage evolution and structural degradation within the granite’s pore-fracture system. A pronounced accelerated transition occurred around a critical temperature of ~110°C, where porosity and connected porosity surged from initial values of 1.08% and 0.36% to 18.51% and 16.24%, respectively. The exceptionally high porosity at 200°C, exceeding typical granite matrix porosity, is attributed to the synergistic enhancement of triaxial stress and seepage pressure on thermal cracking. These findings underscore the significance of nonlinear evolution and accelerated transitions induced by THM coupling, providing essential insights for evaluating the long-term safety of geological repositories.
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