Comparison between laboratory and in situ values of the coefficient of primary consolidation<i>c</i>_v

Abstract

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.Key words: clay, coefficient of primary consolidation, consolidation, embankment.