Several methods have been proposed for determining the value of the maximum consolidation
pressure. They fall under the following categories. They are
- Field method,
- Graphical procedure based on consolidation test results.
The field method is based on geological evidence. The geology and physiography of the site may
help to locate the original ground level. The overburden pressure in the clay structure with respect
to the original ground level may be taken as the preconsolidation pressure pc. Usually the
geological estimate of the maximum consolidation pressure is very uncertain. In such instances, the
only remaining procedure for obtaining an approximate value of pc is to make an estimate based on
the results of laboratory tests or on some relationships established between pc and other soil
There are a few graphical methods for determining the preconsolidation pressure based on
laboratory test data. No suitable criteria exists for appraising the relative merits of the various
The earliest and the most widely used method was the one proposed by Casagrande (1936).
The method involves locating the point of maximum curvature, 5, on the laboratory e-log p curve
of an undisturbed sample as shown in Fig. 7.8. From B, a tangent is drawn to the curve and a
horizontal line is also constructed. The angle between these two lines is then bisected. The abscissa
of the point of intersection of this bisector with the upward extension of the inclined straight part
corresponds to the preconsolidation pressure pc,.