Undrained shear strength response under monotonic loading of Chlef (Algeria) sandy soil

During the last mid-century, the Chlef area was strongly affected by two earthquakes. From the geological context, there were numerous ejections onto the ground level of great masses of sandy soils and large displacements of various forms of some building foundations. These damages are due to soil liquefaction problem. This loss of shear strength can be attributed to many factors. History of recent cases indicates that sand deposited with silt content is much more liquefiable than clean sand. Therefore, a deep understanding of silty sand behavior is needed for the liquefaction assessment of silty sandy soils. Moreover, during seismic shaking, the post-liquefaction behavior of silty sand and, consequently, the stability of structures founded on liquefied soil depend on the steady-state shear strength of soil. The objective of this laboratory investigation is to show the effect of silt contents and the relative density on the mechanical behavior of such soils in monotonic loading. In this context, a series of undrained triaxial tests were performed on reconstituted saturated silty sand samples with different fines content ranging from 0% to 40%. In all tests, the confining pressure was held constant to 100 kPa. The fines content and the global void ratio are expressed by means of the equivalent void ratio. Linear correlations relating the undrained residual shear strength of loose, medium dense, and dense (Dr = 12%, 50%, and 90% before consolidation) sand–silt mixtures to the equivalent void ratio are obtained. The concept of the equivalent void ratio will then be used as a key parameter to express the dilatancy behavior of both clean and silty sand soils. Moreover, from the experimental results obtained, it is clear that the global void ratio cannot be used as a state parameter and may not represent the actual behavior of the soil as well.