Thaw-driven permeability evolution of frozen soil with segregated ice: insights from low-field nuclear magnetic resonance and LBM simulations

In this work, we propose a numerical thawing model, based on the lattice Boltzmann method (LBM), to predict the permeability evolution of the thawing frozen soil with segregated ice. Our numerical model considers the effects of soil pore structures, pore-scale water melting temperature phase change and water migration. We also measured the low-field nuclear magnetic resonance (NMR) responses of the thawing process within different porous media and developed a quantitative relationship between the permeability coefficient and melting temperature considering the heterogeneous feature, adhesive force and temperature-driven force. Our numerical model is first validated at the macroscopic scale using a freezing-thawing experimental setup for temperature distribution and at the microscopic scale using NMR measurements for permeability characterization. Numerical results indicate that the thawing-induced permeability changes in unsaturated frozen soil are closely related to its upper surface temperature and porosity. We find that the greatest liquid mass fraction change at the segregated ice layer is the primary driver of thaw-induced soil settlement. This work will not only bridge the knowledge gap between mesoscopic features and macroscopic hydrological properties of unsaturated frozen soil, but also be beneficial for the large-scale hydrological changes towards climate warming.