Study on deformation characteristics of subgrade loess under pressurized freeze-thaw cycle

• A critical dry density, 1.65 g.cm -3 , is identified to retard frost penetration. • Stability coefficient K is introduced to assess long-term trends. • Critical loading frequency is found at 1.5 Hz. • Hardin-Drnevich model is used to predict the dynamic strength behavior of loess. This study investigates the influence of dry density on the deformation and dynamic characteristics of loess subjected to pressurized freeze-thaw cycles, a common condition in seasonally frozen regions whose underlying mechanisms remain insufficiently understood. Through pressurized freeze-thaw tests under a constant axial stress of 50 kPa on remolded Lanzhou loess specimens with dry densities of 1.60, 1.65, and 1.70 g·cm⁻³, followed by dynamic triaxial tests on the post-freeze-thaw samples, the following key findings were obtained: dry density nonlinearly regulates the deformation and dynamic mechanical response of loess under coupled pressurized freeze-thaw action; the cumulative deformation peaked at a dry density of 1.65 g·cm⁻³, showing a 54% increase compared to that at dry density of 1.60 g·cm⁻³; the variation in dynamic strength is governed by a critical loading frequency of 1.5 Hz; and the Hardin-Drnevich model accurately predicts the skeleton curves. This study innovatively explores the mechanical behavior of frozen loess under the combined action of pressurized freeze-thaw and dynamic loading, and introduces a stability coefficient to assess the long-term stability of subgrades after pressurized freeze-thaw cycles. Its engineering significance lies in providing a theoretical basis for compaction quality control of loess subgrades in seasonally frozen regions, which helps mitigate the adverse effects of pressurized freeze-thaw cycles on subgrade performance.