Evaluating the permeability evolution in a granite fracture by short- and long-term flow-through tests and X-ray CT imaging

This study aims to visualize the evolution of permeability and internal fracture structure of granite under coupled thermal–hydraulic–mechanical–chemical (THMC) conditions. This study investigated the short-term and long-term hydraulic behavior of a fractured granite sample under varying confining pressures and temperatures. X-ray computed tomography (CT) was employed to observe a single fracture during loading–unloading cycles and a 105-day continuous flow-through test, enabling direct visualization of fracture evolution. Flow-through simulations based on CT data were performed to reproduce internal flow patterns, and a coupled THMC model was applied to assess the influence of chemical–mechanical interactions. The short-term tests revealed that the degree of surface matching strongly affected permeability, which exhibited reversible changes during loading–unloading and a pronounced dependence on confining pressure and temperature. In the long-term test, both permeability and CT-measured mechanical aperture decreased, consistent with increased contact ratios, suggesting that pressure dissolution may have reduced fracture conductivity. Flow-through simulations showed that flow paths were governed by aperture variations, while THMC modeling results are consistent with chemical–mechanical processes contributing to permeability reduction. By capturing internal fracture structures in situ during flow-through testing, this study links microstructural evolution to permeability changes under different conditions. These findings provide a mechanistic basis for predicting fracture sealing behavior and can inform the design of geological disposal systems for radioactive waste.