An Improved Model of Soil Response to Load, Unload and Re-Load Cycles in an Oedometer

There are a number of advantages to be gained by representing the oedometric compression of a soil skeleton, during virgin loading, unloading and subsequent reloading by ‘log (v) versus log (p′)’ relationships rather than the conventional ‘e versus log10 (p′)’ expression. The paper presents an augmented version of the basic, two parameter (C′c, C′s), ‘log (v) versus log (p′)’ model in which the addition of two further parameters (C′r, C′o) enables a complete, non-linear response for any load-unload-reload cycle to be reproduced. All four parameters, deduced from a single such cycle in an oedometer, can then be used to predict the response of the sample in any other unload-reload cycles. Results are presented from tests of this kind on a range of fine-grained soils to demonstrate the key attributes of the model. These include the generation of ‘log (mv) versus log (p′)’ diagrams that furnish practically useful mv values applicable throughout any unload-reload cycle. The model also provides a simple means of assessing the overconsolidation ratio of an undisturbed soil sample.