Minimum undrained strength of Hostun RF sand

Abstract

The minimum undrained behaviour of very loose Hostun RF sand is described. The analysis is based on the results of several series of undrained triaxial compression and extension tests. The samples were consolidated isotropically or anisotropically along constant effective stress ratio paths. The initial void ratios at fabrication state and at the end of the monotonic consolidation stage of each test were also evaluated. This experimental study confirms the conceptual framework proposed by Konrad, based only on isotropically consolidated undrained triaxial tests (CIUs) to explain the undrained behaviour of very loose sands during monotonic loading. The systematic evaluation of the experimental errors and sample variabilities using probabilistic techniques assesses the existence of an upper boundary (upper flow) and a lower boundary (lower flow) of the steady state of deformation. This paper extends the scope of the previous framework for sand samples subjected to an initial monotonic consolidation history. The extended framework draws on the instability concept of Lade and the asymptotic stabilization of the effective stress ratio at peak. The minimum undrained strength of Hostun RF sand at steady state is strongly influenced by the normalized mean effective stress at peak, and by the void ratio at the end of the initial monotonic consolidation.