Assessment of Swelling Pressure Determination Methods with Intact Callovo-Oxfordian Claystone

There are several methods for the determination of soil swelling pressure. In this study, such common methods were assessed using intact Callovo-Oxfordian (COx) claystone samples extracted in the direction perpendicular to the bedding plane, in the French Underground Research Laboratory in Bure. Higher swelling pressure was found with the swell-consolidation method, the swelling pressures determined by other methods being comparable. The swelling line that defined the swelling limit was lower than the consolidation curve, confirming the limitation of the swell-consolidation method in determining soil swelling pressure. Moreover, the swelling pressure corresponding to the in situ void ratio was expected to be 12 MPa–14 MPa, while the value corresponding to the sample void ratio after sampling was estimated between 0.3 and 1.9 MPa, much lower than the expected one. This large difference might be attributed to the claystone rebound due to unloading and claystone damage due to sampling. It could be also due to the natural material variability in terms of mineralogy and dry density. Further studies are, thus, needed for clarifying this point.