New model cracks freeze-thaw damage to underground infrastructure

<p>Seasonal freeze–thaw cycles pose major challenges to underground infrastructures in cold regions, where rock fractures exert strong control over subsurface fluid flow, heat transfer, and ice formation. However, the role of fracture–matrix interactions during freezing and thawing remains poorly understood. In this study, we develop a coupled thermo–hydraulic (TH) model with phase change and local thermal non-equilibrium (LTNE), formulated within a finite element framework, to investigate these processes in fractured porous media. The model is based on the discrete fracture network approach, where fractures are represented as lower-dimensional entities embedded within a permeable porous matrix. It can capture ice–water phase change, LTNE heat exchange between fracture fluid and the surrounding rock matrix, as well as latent heat effects and phase-dependent permeability in both fracture and matrix domains. Model verification is conducted against four benchmark problems, addressing fracture–matrix heat exchange under LTNE conditions, ice–water phase change under freezing and melting, and lower-dimensional fracture representation implemented in the proposed TH modeling framework. The model is further applied to problems of increasing complexity, from a single fracture to intersecting fractures and ultimately to a fracture network, to systematically elucidate the roles of freeze–thaw processes in fracture-scale permeability evolution and network-scale flow reorganization. Our results reveal a self-reinforcing feedback mechanism in which freezing blocks secondary pathways, focusing flow into major channels, which in turn suppress further freezing and sustain preferential flow. These findings have important implications for many hydrological, geophysical, and geotechnical applications in cold regions.</p>