A unified approach to link small-strain shear modulus and liquefaction resistance of pumiceous sand

Abstract

Natural pumiceous (NP) sands containing pumice particles, a type of volcanic soil, are commonly found in the central part of the North Island in New Zealand. The pumice particles are highly crushable, compressible, lightweight and angular, making engineering assessment of their properties problematic. In this paper, several series of bender element and undrained cyclic triaxial tests were performed on reconstituted and undisturbed NP sands to determine their small-strain shear modulus (Gmax) and cyclic resistance ratio (CRR). Furthermore, similar tests were also conducted on normal hard-grained sands (e.g., Toyoura sand) for the purpose of comparison. The results showed that the NP sands have considerably lower Gmax compared to normal sands, resulting in their higher deformability during the initial stages of the cyclic loading test. The high angularity of NP sands play an important role toward the end of the cyclic loading and contributed to their higher CRR. Next, the ratio of CRR/Gmax for each sample was correlated to a level of strain denoted as cyclic yield strain (εay), which was found to be significantly dependent on the percentages of pumice particles present in the natural soils. On the other hand, the εay was found to be less sensitive to the consolidation stress (σ′c) and the relative density (Dr) of the materials. For example, over different values of σ′c and Dr, NP sands have substantially higher values of cyclic yield strain due to their lower Gmax and higher CRR when compared with those of ordinary sands.