A multi-linear approach to strength and plasticity states between the Atterberg limits

The separate plasticity or consistency states between the liquid and plastic limits originally introduced by Atterberg and Terzaghi have long been disregarded, with just one state, plastic, currently acknowledged. The semi-logarithmic relationship between undrained shear strength and liquidity index often considered as a unique straight line is shown to be more realistically represented by a multi-linear approach with much better correlation compared to the single line usually adopted. This approach produces more accurate shear strength values at the liquid and plastic limits compared to those obtained from a single line. The trilinear interpretation of liquidity index against undrained shear strength (fall cone and lab vane) delineates very soft and soft transitions. The stiff transition and a tentative measure of the sticky or adhesion limit have been derived from the author's toughness tests. The plastic range can then be separated, as originally suggested, into consistency regions marked by very soft, soft and stiff transitions and adhesive and non-adhesive states distinguished by the adhesion limit. The adhesion limit deserves further investigation as it represents a significant change of state.