Influence of pumice and fines contents on the extent of particle crushing in pumiceous sand-silt mixtures during undrained cyclic triaxial loading

Abstract

Pumiceous particles have a distinct vesicular nature as well as a complex surface texture that makes them potentially vulnerable to crushing under cyclic loading. Pumiceous sand mixtures have received more scientific attention than pumiceous silts in this regard. Researchers have found the undrained cyclic behaviour of pumiceous sands to be significantly different from that of hard-grained sands because of the particle crushing that occurs during cyclic testing and/or sample reconstitution. The liquefaction resistance of pumiceous sands is also considered to be higher because of the pore-water pressure distribution in the sample that occurs during particle crushing. The undrained behaviour of pumiceous silt has only been studied once previously: such material did not crush during sample reconstitution and undrained cyclic testing, which was attributed to a cushioning effect taking place between silty, non-crushable particles and coarse sandy pumice particles. Whether there are thresholds of fines content and/or pumice content at which pumiceous soil mixtures start to behave more similarly to hard-grained soils are yet to be unravelled and remain relevant for engineers and scientists. This paper analyses particle crushing after sample reconstitution and undrained cyclic triaxial testing of three pumiceous natural soil mixtures (lacustrine tephra deposits) from northern New Zealand having fines (< 0.075mm) and pumice contents ranging between 20% and 70% and 30% and 51%, respectively. The results examine potential changes in (1) fines content, (2) pumice content, and (3) undrained cyclic behaviour by comparing both pore-water pressure and axial strain development of the pumiceous soils with other crushable and non-crushable soils.