E3S Web Conf.
Volume 92, 20197th International Symposium on Deformation Characteristics of Geomaterials (IS-Glasgow 2019)
|Number of page(s)||6|
|Section||Geomaterial Behaviour: Compressibility and Time-dependency|
|Published online||25 June 2019|
Genuine and false pre-consolidation and yield pressures
Retired Civil Engineer, formerly Senior Lecturer at University of Auckland, New Zealand
“It remains a mystery why the international profession still uses the awkward e-log p plots, and the incomplete and useless coefficient Cc which is not even determined from the measured data, but from a constructed line outside the measurements”. These are the words of Nilmar Janbu (1998). This paper does not solve the mystery; what it does is highlight the issue behind the mystery in the hope that the profession will face up to the defects of the log scale. An examination is made of oedometer test results when plotted to both scales. Examples are given for sedimentary and residual clays, and sands. It is shown that the e-logp plot routinely produces graphs from which pre-consolidation pressures or yield pressures can be determined. However, when plotted using an arithmetic (linear) scale, this apparent pre-consolidation or yield pressure is found, in most cases, to disappear. It is a false value created by the way the data are plotted. The paper does not deny that pre-consolidation or yield pressures exist in many soils; it gives examples for each of the soil types listed above. It is recommended that the term “yield pressure” be used in preference to “pre-consolidation pressure”, and that only the use of a linear scale will reveal whether such a pressure exists.
© The Authors, published by EDP Sciences, 2019
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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