Evaluating friction angles for clays: piezocone tests compared with Atterberg limits

A limit plasticity solution for evaluating the effective stress friction angle in clays from piezocone tests was assessed and compared with the popular notion of using laboratory Atterberg limits on remoulded specimens. The results showed that the in situ piezocone-based method provided a far more accurate and robust interpretation of the friction angle values of 155 separate clays than empirical correlations with plasticity index when compared with laboratory benchmark values obtained from triaxial compression tests. For illustration, the piezocone-based method was shown successfully to capture the effective stress parameter of four clays with friction angles of 20–37°: normally consolidated kaolin clay in chamber tests; natural soft clay deposit located at Bothkennar, UK; Troll offshore clay in the North Sea; and soft plastic lacustrine deposits in Bogota, Colombia.