Critical State Lines of Portuguese liquefiable sands

The Critical State framework has been used to describe the behaviour of sands and study the liquefaction susceptibility of these soils when sheared in static and cyclic conditions. The ocean coast and some fluvial basins of Portugal are characterised by the presence of sandy deposits that, combined with a moderate to high seismic activity, creates the conditions for moderate to high liquefaction susceptibility. The aim of this work is to study and compare five Portuguese liquefiable alluvial sands, collected in the centre-south of the continental territory. The experimental programme included a complete physical identification of the five materials and a series of triaxial tests in drained conditions. The specimens were prepared at a high initial void ratio (loose), using the moist-tamping technique with an appropriate initial water content, reaching void ratios close or slightly higher than emax. The specimens were fully saturated, isotropically consolidated and statically sheared at constant strain rate until reaching the critical state. Shear wave velocities after consolidation were measured using bender elements. The critical state and small-strain stiffness parameters are discussed and compared, evidencing the differences between these soils. Relationships between some of these parameters and physical characteristics are obtained