Comprehensive analysis of pumice sand: physical, chemical, and mechanical behavior under static and cyclic triaxial testing

Pumice sand is a highly porous and crushable volcanic soil widely distributed in volcanic regions such as Japan, where it may contribute to earthquake-induced ground deformation, liquefaction, and slope instability. However, the coupled effects of particle crushability, density, and confining pressure on its monotonic and cyclic behavior remain insufficiently clarified, resulting in uncertainty in geotechnical design for volcanic deposits. This study investigates the mechanical characteristics and liquefaction resistance of pumice sand obtained from Miyakonojo City, Miyazaki Prefecture, Kyushu, Japan. A comprehensive laboratory testing program was conducted, including chemical analysis, single-particle strength tests, one-dimensional consolidation compression tests, static and cyclic triaxial tests. The results show that the tested pumice sand is predominantly composed of silica (SiO 2 ) and has considerably lower particle strength than conventional sands such as Toyoura sand and carbonate sand, confirming its highly crushable nature. The consolidation response indicates a yield stress intermediate between typical sand and clay-like behavior, reflecting the influence of its porous particle structure. Static triaxial tests reveal that particle crushing is more pronounced under drained conditions than under undrained conditions. Cyclic triaxial tests further demonstrate that liquefaction resistance is governed by relative density and confining pressure, with denser specimens requiring a greater number of loading cycles to reach liquefaction. In addition, lower confining pressure results in higher apparent liquefaction resistance, which may be attributed to reduced particle crushing during cyclic loading. These findings clarify the distinctive mechanical response of pumice sand and provide an experimental basis for improving liquefaction assessment and geotechnical design in volcanic regions.