Influence of inter-granular void ratio on monotonic and cyclic undrained shear response of sandy soils

Liquefaction of sandy soil deposits during earthquakes has been one of the most important problems in the field of geotechnical earthquake engineering. A major challenge is the assessment of the appropriate undrained shear strength of liquefied soils to be used in the study of liquefaction stability of different types of earth structures (embankments, earthdams, etc.). The objective of this laboratory investigation is to study the effect of the inter-granular void ratio on the phase transition state undrained shear strength of loose, medium dense and dense (D(r) = 12, 50, and 90%) sand-silt soil mixtures under monotonic loading and liquefaction potential under cyclic loading. For this purpose, we considered the matrix of sand with fines as a combination of two sub-matrices: a coarser grain matrix and a finer grain matrix. Moreover, series of undrained triaxial compression tests were carried out on reconstituted saturated silty sand samples with fines contents ranging from 0 to 50%. The results show that the global void ratio does not reflect the real behaviour of the soil and the undrained shear strength at the phase transition state can be correlated to the inter-granular void ratio of the sand-silt mixtures up to 50% fines content. Indeed, it decreases linearly with further increase in the inter-granular void ratio. The results of the undrained cyclic tests confirm this tendency. (C) 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.