Experimental study on permeability characteristics of clay-gravel mixtures under freezing-thawing actions in core wall of earth-rock dams

Clay-gravel mixture is generally used as the compacted impermeable material in the core wall of high earth-rock dams. In high cold regions, it will endure severe freeze-thaw actions during the construction process. In this study, a series of triaxial permeability tests were performed to investigate the evolution law of permeability characteristics after freeze-thaw cycles. The results show that:(1) the permeability coefficient increased significantly after freeze-thaw cycles, and the degree of increase was controlled by various factors such as confining pressure, number of freeze-thaw, gravel content and the initial molding water content;(2) the 1st-2nd cycle of freezing-thawing has the most prominent influence on the increase of permeability;(3) a lower confining stress and a higher molding water content will dominate the increase of permeability induced by freeze-thaw actions;(4) the effect of gravel content on the permeability is closely related to the inner meso-structural distribution of clay-gravel particles;(5) the freeze-thaw triggered variation of permeability will significantly increase with increasing the initial molding water contents, and a greater increasing amplitude will be found on the dry side of optimum water content, while a smaller amplitude on the wet side. The results can provide useful guidance for the design of impervious structures in high earth-rock dam as well as the prevention of freeze-thaw damages during its construction in winter. © 2021, China Water Power Press. All right reserved.