Effect of freeze-thaw cycles on mechanical properties of compacted volcanic ash

Volcanic ash is a potential fill material for subgrade to replace traditional materials which contributes to resource conservation and sustainable development. In seasonally frozen regions volcanic ash inevitably is exposed to the effects of freeze and thaw, such as in China's Changbai Mountains. In order to investigate the mechanical behavior of compacted volcanic ash during temperature variations, 72 groups of closed-system freeze-thaw cycle tests and triaxial shear tests with different water contents were conducted in this study. The stress-strain rela-tionship for volcanic ash is strain-softening, and the softening degree decreases with the number of freeze-thaw cycles and water content. The results show that the mechanical parameters of volcanic ash decrease firstly with the number of freeze-thaw cycles and remain relatively stable when 10 freeze-thaw cycles elapsed. Mechanical degradation is primarily caused by the loss of inter-particle bonding forces in volcanic ash by freezing and thawing. The maximum drops in elastic modulus, peak friction angle, cohesion and internal friction angle were 54%, 7%, 20% and 4% respectively. Empirical formulations are fitted by binary quadratic equations that describe the relationship between mechanical parameters of volcanic ash and the number of freeze-thaw cycles as well as the water content. The findings can provide a reference for the construction of projects related to volcanic ash as a potential building material in seasonally frozen regions.