Effects of soil fabric and particle strength on cyclic resistance ratio and shear moduli of the volcanic soils

The 2018 Hokkaido Eastern Iburi earthquake, along with several previous seismic events, caused liquefaction-induced damage on grounds that are composed of volcanic soils. These soils are characterized by their composition of fragile particles that are highly susceptible to crushing, making the evaluation of their liquefaction resistance particularly important. Liquefaction resistance of volcanic soils is thought to be closely related not only to soil density but also to the soil fabric effect and particle crushability. In this study, volcanic soil samples collected from Hokkaido, Japan, were subjected to shear wave velocity measurements, cyclic undrained triaxial tests, particle size distribution tests, and single-particle compression tests. The specimens for the triaxial tests were prepared using two different methods: dry tamping and wet tamping, with densities adjusted to match in-situ conditions. Some specimens were also subjected to over-consolidation history prior to cyclic undrained loading. The results demonstrated that both the small strain shear moduli, G 0 , and cyclic resistance ratio, CRR , were significantly affected by the soil fabric effect caused by the specimen preparation methods and over-consolidation history, despite the specimens having approximately the same densities within each sample series. Furthermore, the authors investigated the relationship between the change ratios of G 0 and CRR due to the variations in the soil fabric effect. As a result, it was confirmed that a volcanic soil sample with extremely low single-particle strength deviated from the trend observed in typical hard-grained sandy soils and other volcanic samples with higher single-particle strength. These findings suggest that particle crushability and deformation characteristics may play a critical role in the cyclic undrained behavior of volcanic soils.