A Simple Method to Calculate the Void Ratio of Very Loose Silts and Silty Sands in Torsional Shear Hollow Cylinder Testing

The determination of the critical state locus (CSL) via triaxial testing has become a key input to the current state of practice to characterize the liquefaction susceptibility of tailings. However, an accurate estimate of void ratio is required to infer the CSL and allow correlation of the expected in situ state to element laboratory testing. This is an issue of particular importance for the loose moist tamped specimens generally used for CSL testing, which undergo significant volumetric collapse during saturation—a volume change that is difficult to measure using conventional test techniques. The torsional shear hollow cylinder (TSHC) device has been adopted in the past to investigate the effect of cross-anisotropy on the strength of soils, although studies on tailings in the TSHC are limited. The void ratio in previous TSHC testing programs appear to have been based on initial dimension measurements, with or without the adoption of internal instrumentation. However, as silty sands and sandy silts prepared in a loose state experience collapse during saturation, this may introduce an unquantifiable error in void ratio if the initial dimensions method is adopted and volumetric change due to saturation is not properly considered. A procedure is proposed in this paper that provides simple steps and calculations to enable the determination of void ratio in the TSHC apparatus in specimens that undergo significant volumetric collapse on saturation. This method is potentially more accurate than methods based on initial dimensions measurements to infer void ratio and does not require costly internal instrumentation.