Abstract:
The shear stress of stiff or dense soils increases with the displacement and reaches itsmaximum value, and then shear stress decreases and remains a constant value. The minimumand constant shear stress of soils reached at large shear displacements is called as residualshear strength. Residual shear strength generally has a great importance in design ofengineering structures constructed on fissured overconsolidated clays and long-term slopestability analysis in geotechnical engineering. In laboratory testing, modeling the residualconditions of a soil requires large shear displacements attained in drained conditions.Reversal direct shear test (RDS), consolidated-drained triaxial test (CD) and torsional ringshear test (RS) are the widely used testing methods to determine residual shear strengthparameters. These methods have some advantages or limitations when compared with eachother. In this study, residual shear strength parameters of soil samples having different clayfractions were determined by the three different drained tests, the results were compared, andeffect of the testing methods on residual shear strength was investigated. The variation ofresidual shear strength angle versus liquid limit and plasticity index were studied. The resultswere compared with previous studies. As a result, it is found that the residual shear strengthangle determined by the ring shear test is lower than the others, and the residual shear strengthangle decreases with the increasing liquid limit and plasticity index.
