Work as a criterion for determining in situ and yield stresses in clays

Abstract

A method of interpreting conventional oedometer test data using work per unit volume as a criterion for determining both in situ effective and yield stresses in clay is presented. This technique was applied to the results of oedometer tests carried out on samples of natural clay deposits and on specimens consolidated anisotropically from a slurry to a known effective stress state. The work per unit volume – effective stress relationship, using arithmetic scales, can be approximated or fitted using linear relationships. The intersections of these fitted lines are demonstrated to provide accurate values for in situ current and yield (preconsolidation) stresses. The yield stress is defined as the intersection of the initial fitted line and the linear relationship observed at higher stresses. The current effective stress is indicated by the first significant divergence of the data from the initial fitted line. These relationships apply to both conventionally (horizontally) trimmed specimens and to vertically trimmed oedometer samples. It is hypothesized that the in situ effective and yield stresses (in both the vertical and horizontal directions) in a natural clay can be determined by the work per unit volume interpretation of oedometer tests carried out on horizontally and vertically trimmed specimens. Key words: in situ, stress, yield, oedometer, interpretation, clays, work, state, K0, preconsolidation pressure.