Practical guidelines on the determination of one-dimensional swell properties of highly expansive clays

Engineers typically require two parameters for the understanding of expansive soils to limit damages invoked by volume change: the swell pressure – the stress required to completely restrain volume change upon inundation – and the swell potential – the volume increase exhibited upon inundation at a given stress level. These properties have been shown to be dependent on the stress path followed during their measurement in the laboratory. This creates challenges for practitioners to obtain reliable swell properties without an extensive testing programme. A discussion of the stress path-dependency and reasons for variations of the measured swell properties within a Barcelona Extended Model (BExM) framework is given. Series of oedometer tests following three standard methods for the determination of swell pressure and swell potential were carried out for two highly expansive clay soils with different microfabric types. After swell phases, samples were consolidated to high stresses (up to 4 MPa). The magnitudes of the experimentally measured swell properties relative to one another using the different methods aligned with the predicted hierarchy according to the theoretical framework for both soils, verifying its appropriateness for both microfabric types. The results and framework were used to design a minimum testing programme for robust determination of the swell pressure and swell potential of a given clay for industry applications.