Estimation of parameters of Santos marine clays using Piezocone and Vane Tests

Faiçal Massad¹

¹ Escola Politécnica da USP

Baixar PDF doi:10.20906/CPS/CB-01-0088

Resumo

1. Introduction The paper deals with the estimation of geotechnical parameters such as pre-consolidation pressure and undrained shear strength (su) of marine clays based on field tests (CPTU and Vane Test) and in the light of their geological history. Supported by the observation of a linear variation with depth of the CPTU corrected tip resistance (qt), the author ([1] and [2]) presented a simple formula to estimate the Kulhaway and Mayne [3] empirical factor Nst successfully applied to Santos clays. As it is known, this Nst factor depends on the type of soil, its origin and correlation with results of consolidation tests on undisturbed samples of good quality. The same was observed with the undrained shear strengths from Vane Tests that increase linearly with depth, with growth rates (c1) that depend on the submerged densities of the clays [1]. It is in this context that the knowledge of the marine clays origin is introduced and, in particular, their preconsolidation mechanisms, chiefly, preterit sea level variations and dune action. These mechanisms are reflected in correlations with depth of pre-consolidation pressures, the undrained shear strength (su) and oedometer Young´s moduli (Eoed and Eur), of great importance in the application of some rheological models of soils, such as Hardening Soil Model. As recommended by Demers and Lerouiel [4], geological and geotechnical knowledge should be considered when dealing with such correlations. 2. Final Remarks Based on the geological history of marine sediments from Santos Plain, Brazil, the work presented formulae to estimate the empirical factors Nst (of Kulhaway and Mayne) and Nkt and thus determine both the pre-consolidation pressure and the undrained shear strength (su) through CPTUs. In both cases, the formulae are very simple. A practical application was made using the FOSM (First Order Second Moment) method for comparisons. In addition, it was shown that the a and b parameters of Kuwalhay and Mayne, which allow the estimate of the Eoed and Eur moduli

Palavras-chave: Geological History; soft clays; CPTU; Vane Test; Consolidation test