Experimental investigation on mechanical properties and permeability evolution law of frozen calcareous clay under fluid-solid coupling

In the Huainan-Huaibei deep tundra mining project, groundwater seepage and complex geostress significantly challenge construction safety. To systematically investigate the mechanical properties and permeability evolution of frozen ground under coupled in-situ stresses and groundwater effects, this study performed triaxial compression seepage tests on frozen calcareous clay under varying confining pressures and pore water pressures using a high-pressure rock triaxial testing system. Test results show that under fluid-solid coupling, the deviatoric stress versus axial strain curve of frozen calcareous clay displays strain hardening behavior. Furthermore, at constant confining pressure, both the slope of the stress-strain curve and the peak stress negatively correlate with pore water pressure. Circumferential strain response depends on confining pressure levels: it increases with pore water pressure under low confining pressures but decreases at high confining pressures. The study reveals that during loading, permeability of frozen calcareous clay dynamically decreases from the initial permeability ( K ₀) to the minimum permeability ( K min ), remains low for a phase, and then sharply increases to the maximum permeability ( K max ), with this peak corresponding to the specimen failure moment. Within a specific range, pore water pressure positively correlates with permeability at three representative time points in frozen soil specimens, whereas confining pressure shows a negative correlation. Concerning strength, at constant confining pressure, increasing pore water pressure reduces frozen soil strength; however, the weakening effect lessens as pore water pressure rises further. At constant pore water pressure, frozen soil strength positively correlates with confining pressure. This research quantifies the seepage-mechanical response of frozen ground under fluid-solid coupling and can be validated by field monitoring data from mine frozen wall projects. The developed permeability evolution model captures the mechanical and seepage behavior of frozen ground under complex conditions, offering essential theoretical support for the design and safety assessment of deep mine frozen walls.