Nonuniform frost heave of saturated porous rocks in cold regions during cyclic unidirectional freeze-thaw: influence of the temperature gradient

Freeze-thaw is the most common weathering phenomenon in cold regions and the primary cause of slope landslides, tunnel damage, and open-pit mine instability. The nonuniform frost heave and cumulative effect of the freeze-thaw of rocks are the key factors causing en- gineering frost damage. This study designed a cyclic freeze-thaw system with non-uniform temperature fields. The nonuniform freeze-thaw deformation of sandstone, granite, and basalt in cold regions was assessed under different freezing temperature gradients. Results indicated that the three types of rocks exhibited nonuniform frost heave between parallel and vertical temperature gradient directions under the influence of the freezing temperature gradient. The frost heave strain in the different directions increased considerably with the increasing temperature gradient. Among the three materials, red sandstone had the highest nonuniform frost heave, followed by granite porphyry and basalt. The stronger the frost heave property of the rock, the higher the nonuniform frost heave coefficient, and the greater the effect of cyclic freezing and thawing. The peak and residual frost heave strains of the rocks with freezing temperature gradients increased nonlinearly with the increase in the number of freeze-thaw cycles. Freezing and thawing caused irreversible plastic frost heave deformation in the different directions. Simultaneously, the growth rate of frost heave strain under cyclic freeze-thaw cycles increased with decreasing the freezing temperature and increasing temperature gradient. The temperature gradient formed by the unidirectional freezing pattern unique to engineering rock bodies was the main cause of nonuniform frost heave.