Undrained shear strength correlation analysis based on vane tests in the Jacarepaguá Lowlands, Brazil

Abstract

The test sites analyzed here consist of clay deposits located in the Jacarepaguá Lowlands in Rio de Janeiro, characterized by high plasticity, high compressibility and low undrained shear strength. The deposits are made up of lightly overconsolidated aged clays, montmorillonite being the predominant clay mineral. Soft clay deposits are usually superficial, with thicknesses generally varying between 6 m and 17 m and geologically recent and originated from marine regressions and transgressions, that occurred between 6000 and 3500 years ago. The objective of this study is to analyze a large database of undrained shear strength measurements obtained by 461 vane tests performed at 15 different sites. In general, most of the data correspond to very soft clays, with undrained shear strength values lower than 25 kPa. The undrained shear strength measurements are correlated with plasticity index and with maximum excess pore pressure, measured with piezocone tests. The method for estimating the undrained shear strength s_u(DT) of soil from the excess pore pressure generated during piezocone dissipation tests proposed by Mantaras et al. (2015) was validated against the vane test database.

Keywords
Organic soil; Piezocone test; Plasticity index; Undrained shear strength; Vane test; Soft soil