Measured coefficient of consolidation field and laboratory values of very soft to soft marine Santos clay for wick drain design

Jean-Pierre Paul Rémy, Vitor Nascimento Aguiar

Dans les comptes rendus d’articles de la conférence: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: In Situ Testing

ABSTRACT: Very reliable compressibility parameters of the very soft marine clay of Santos, Brazil, have been obtained from good quality standard and special oedometer tests that can be used to estimate the total primary and secondary compressions of the clay under a containers terminal to be built close to Santos harbour. Although the geotechnical study of the site has been very thorough and has provided quite complete and reliable data about the soft layer properties, the drastic reduction of the coefficient of consolidation in the stress range around the preconsolidation stress makes it very difficult to define the representative value of the coefficient of consolidation needed to design the proper combination of wick drains pattern/surcharge stress/preloading time needed to bring the terminal operation settlements down to acceptable values taking into account the simultaneous occurrence of primary and secondary consolidations.

RÉSUMÉ: Des paramètres de compressibilité trés fiables de lès molle de Santos au Brésil, ont èté obtenus à partir s conventionnels et spéciaux qui peuvent être utilisés pour estimer les compressions primaire et secondaire de argile sous un terminal de conteneurs qui doit être construit prêt du port de Santosgéotechnique du site ait été exhaustive et ait fourni des données bien complètes et fiables sur les propriétés de la couche molle, he de la contrainte de préconsolidation rend très difficile le choix de la valeur coreprésentative du coefficient de consolidation à utiliser pour le projet du trinôme nécessaire pour amener les tassements du ration à des valeurs acceptables, prenant . 1. INTRODUCTION Rémy et al (2010a, 2010b) report the results of good quality standard oedometer tests and special oedometer tests and the backanalysis of the measured layers compressions under a pilot embankment during a period of two years following beginning of construction, of a very soft to soft marine clay in Santos (Brazil). The backanalysis focused mainly on the measured compressions of the most critical soft clay layer under the three embankment areas, area 1 with wick drains on a 1.2 x 1.2m square mesh, area 2 with wick drains on a 2.4 x 2.4m square mesh and area 3 with no wick drains, and was based on the working hypothesis that secondary consolidation occurs simultaneously with primary consolidation. The soil profiles under area 1 (with 1.2m x 1.2m wickdrains) and under area 3 (without wickdrains) are shown in figure 1. The most critical layer is layer number 6 described as silty clay, slightly sandy. 2. COMPRESSIBILITY PARAMETERS OF THE SOFT CLAY LAYER The results of the standard oedometer tests are illustrated in figure 2 which shows the strain () plotted against the logarithm of vertical effective stress (log v) for eight standard oedometer tests run on sample (6) of boring SRA-203 which position, in area 3, can be seen in figure

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