Index Test Method for Estimating the Effective Preconsolidation Stress in Clay Deposits

The effective preconsolidation stress (sigma'(p)) of clay is classically determined from one-dimensional consolidation tests on undisturbed samples but a first-order approximate value can be estimated from its plasticity and water content characteristics. In this paper, initially a twofold simple empirical model for predicting sigma'(p) that bifurcates at an overconsolidation ratio (OCR) of 3 is developed, and then its validity and generality are evaluated using an external (independent) validation data set that includes 500 records from 50 different sites. The proposed model is accompanied by a discriminant function that uses water content and plasticity characteristics to separate soils with OCR < 3 (contractive) versus soils with OCR >= 3 (dilative). The results of applying the new and existing simple empirical models to the validation data set indicate that the predictive capability of the new model is quite superior to prior existing approaches that have unacceptable performance. (C) 2016 American Society of Civil Engineers.