DSHANSEP: Alternative considerations of the SHANSEP approach

Abstract

Since it was first proposed by Ladd and Foott in 1974, the SHANSEP approach has become a quite useful and convenient approach for the evaluation of the undrained shear strength of clay soils in-situ. SHANSEP is commonly practiced with determination of its parameters using various correlations based on consistency limits. While seemingly handy, such correlations hide some details of the behaviour of clayey soils that are useful for engineering judgement. In this article, an alternative way of looking at the SHANSEP method is presented by examining an integrated framework for strength behaviour of clays. This resulted in a new approach called DSHANSEP, where the D represents the so-called “dilatancy parameter” which measures changes in pore pressure due to changes in shear stresses during undrained loading. The resulting association with dilatancy is logical as this parameter reflects failure mechanisms of the clays which is integral aspect of the undrained shear strength of clays. The implication of this relation is explored by looking at its dependence on the overconsolidation ratio, the mobilized stress ratio and sample quality. Furthermore, a formalized system of classification for clays based on the dilatancy parameter and their overconsolidation ratio is proposed and applied for Norwegian clays along with suggested parameters. Use of DSHANSEP and the proposed classifications are in line with the safety philosophy adopted for stability of slopes involving soft clays in Norway.