Effective friction angle of clays and silts from piezocone penetration tests

Abstract

An existing effective stress limit plasticity solution for piezocone penetration tests (CPTu) is calibrated to evaluate the effective stress friction angle ([Formula: see text]) for undrained conditions for a variety of fine-grained soils ranging from natural lean to plastic clays and clayey silts from marine, alluvial, lacustrine, deltaic, and glaciofluvial origins. Data from 105 clay sites are compiled to examine the CPTu-interpreted [Formula: see text] values in comparison with laboratory benchmark values obtained from undrained consolidated anisotropic (CAUC) and undrained compression (CIUC) triaxial tests made on undisturbed samples. An approximate inversion of the theoretical solution is developed to allow profiles of [Formula: see text] to be evaluated with depth. Five well-documented case studies in Illinois, Louisiana, South Carolina, Ireland, and Massachusetts are presented to illustrate the application of the solution. Lastly, results from 1g chamber tests involving kaolin and kaolinitic–silica mixtures tested by miniature piezocone probes are shown for additional verification.