Numerical simulation study on the evolution of the temperature field and frozen wall in fractured rock mass

Abstract

Artificial ground freezing (AGF) method is a ground reinforcement and waterproofing technique employed in underground engineering to address complex geological conditions. Such strata typically encompass fractured rock mass with intricate fracture networks, where groundwater permeates fractures to form high-velocity dominant flow. Variations in fracture conditions significantly impact both the development of frozen walls and subsequent construction safety; however, current AGF-based numerical simulations rarely consider the influence of fracture seepage on the freezing process. To address this gap, a thermal-hydraulic coupled model for freezing pipes acting on fractured rock mass incorporating fracture phase transition is developed in this study. The effects of fracture aperture, flow velocity, and inclination on the thermal-hydraulic field and frozen wall evolution are simulated, and the results are validated against existing physical model test data. The duration for the two scenarios ranged from 7.0 to 55.9 days and 5.1 to 55.9 days, respectively. Fracture inclination modifies the affected zone around freezing pipes; thus, the frozen wall development rate of a 40° inclined fracture decreases by 92.5% compared to a horizontal fracture. However, the phase transition extent is a dominant factor for heat transfer in fractured rock mass compared to the aforementioned fracture conditions. Temperature distributions within fractures from numerical simulation closely match physical model test results, while the discrepancy in frozen wall development rate diminishes as fracture flow velocity increases.