Evaluation of stress history and undrained shear strength of three marine clays using semi-empirical methods based on Piezocone Test

Abstract

The paper presents a comparative study between semi-empirical methods for the estimation of pre-consolidation pressure and undrained shear strength from Piezocone (CPTu) data. The first method, proposed by Massad, was developed from observing the variation of these parameters with depth; the second method, proposed by Mayne, was developed from simplifications and relationships between the Spherical Cavity Expansion Theory (SCET) and the Critical State Theory; the third method was proposed by Mayne, which considers the variations due to soil type from the CPT Index to estimate the pre-consolidation pressure. The methods were validated based on their applications to the marine clay from Santos Coastal Plain, Brazil, Bothkennar clay from Scotland, and Torp Clay from Sweden. It is intended to verify if the results are consistent with each other, with the stress history of these soils and with the available test results. The application of the Massad’s method led to results close to the available reference values. The results of the Mayne’s method based on SCET showed great variability in behavior comparing to the test data depending on the case study. By the Mayne’s method based on CPT Index values, the calculated pre-consolidation pressures were slightly higher than the values of the available test data. The variations in the results highlighted the importance of validating estimates based on semi-empirical methods through specific tests and the knowledge of geological history contributes to predicting the behavior of clays, since they showed good agreement with the available data from oedometer tests.