Comparison between laboratory and in situ values of the coefficient of primary consolidation cv

Many curve-fitting procedures based on the Terzaghi uncoupled consolidation theory have been proposed for determination of the laboratory coefficient of primary consolidation, c(v). This paper presents data from 10 oedometer tests performed on clay samples from three different sites, with the c(v) values having been obtained using four different fitting procedures. The in situ settlements of the clay layers were measured using borehole extensometers. In this way the in situ c(v) values of the same clay were determined and compared with the laboratory values. At times, the four methods show considerable differences in the values of c(v) determined in the laboratory. Casagrande's method gives values that differ from those of the other methods and is not always easily usable. The other three methods provide a more consistent evaluation of the values c(v). The comparison between in situ and laboratory c(v) values is not straight forward, since these findings show that the macrostructure of the soil layer influences the behaviour of the whole layer, and the laboratory c(v) values, apart from the method used for their determination, are sometimes unable to interpret settlement over time.