Compressibility and consolidation properties of Santos soft clay near Barnabé Island

Abstract

A geotechnical study based on characterization tests and seventy incremental loading one-dimensional consolidation tests was carried out on high-quality undisturbed samples taken from Santos Harbor Channel subsoil near to Barnabé Island, where a pilot embankment was built. The characterization profiles revealed a stratigraphy following the pattern described by Massad (2009), with a 9 m-thick fluvial-lagoon-bay sediments (SFL) clay layer. The consolidation tests were performed following two loading criteria. In criterion A (series one tests), a new loading was applied whenever the strain rate ($\dot{\epsilon }$) reached 10^-6 s^-1, the highest integer power of 10 after the “end of primary” consolidation for double drained 2 cm-thick specimens. In criterion B (series two tests), the standard procedure of 24 hour-long stages was adopted. Criterion A reduced the total duration of the consolidation tests from ten to about three days. The preconsolidation (yield) stress (σ’_p) and the compressibility parameters C_c and C_r obtained from “e versus σ’_v (log)” compression curves of all tests are provided. Series two tests showed that the 24-hour “e versus σ’_v (log)” compression curves are translated to the left of the $\dot{\epsilon }$ = 10^-6 s^-1 “e versus σ’_v (log)” compression curves, keeping C_r and C_c average values unchanged, but decreasing σ’_p by about 8%. The SFL clay C_c/(1+e₀) values obtained herein are higher than those presented by Massad (2009) due to the higher-quality samples tested in this study. It is shown that it is feasible to carry out a high-quality laboratory test program for design purposes following current standards.

Keywords
Santos soft clay; Geotechnical characterization; One-dimensional consolidation test; Sample quality; Remolding effects; Strain-rate effects