DETERMINATION OF PRECONSOLIDATION PRESSURE

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Several methods have been proposed for determining the value of the maximum consolidation
pressure. They fall under the following categories. They are

  1. Field method,
  2. Graphical procedure based on consolidation test results.
    Field Method
    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
    parameters.
    Graphical Procedure
    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
    methods.
    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,.
DETERMINATION OF PRECONSOLIDATION PRESSURE 1
Method of determining pc by Casagrande method

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