This article presents an experimental study on 81 specimens made from three different mixtures of clay and sand. To ensure uniform initial parameters, all specimens were prepared with an initial water content of 30%. Two series of unconsolidated undrained shear tests under different overconsolidation ratios were conducted on a direct shear apparatus: the first aims to determine the SHANSEP (Stress History and Normalized Soil Engineering Properties) parameters namely S and m, whereas the second is used for evaluating the preconsolidation pressure. This work has provided an opportunity to investigate the influence of sand content on SHANSEP parameters and moreover to study the reliability of the preconsolidation stress estimated by the SHANSEP procedure.