The effect of plasticity on residual shear strength for high plasticity clays

The minimum and constant value of shear stress attained at large displacements is defined as residual shear strength (RSS) of soils. For especially over-consolidated fissured clays, as the shear deformation increases the shear stress firstly reaches to a peak value, and then gradually decreases to a constant value. RSS is useful for analyzing the pre-failed slopes in fissured clays and the progressive failures. Reversal Direct Shear and Ring Shear Tests are well-known methods to obtain the RSS parameters in the laboratory. Previous investigations reveal that RSS is affected by mineralogy, effective normal stress and shear rate. As the main affecting parameter is mineralogy, a relationship between consistency limits and RSS could be established indirectly. In this study, Reversal Direct Shear and Ring Shear tests were carried out on 31 clay samples having different plasticity characteristics to determine the RSS parameters. Tests were conducted at least at three different vertical stress levels at shear rates of 0.02 - 0.03 mm/min on the high plasticity clays (CH) samples prepared with slurry consolidometers. The variations of RSS parameters versus consistency limits were studied. Some correlations were established for practical purposes and the findings were compared with the previous studies..