Centrifuge modelling of an expansive clay profile using artificial fissuring to achieve realistic swell magnitudes in a short timeframe

Abstract

This paper presents the results of a centrifuge study in which swell of an expansive clay profile was induced in the centrifuge. A factor which has previously hindered such research is the time required to induce significant swell in-flight, within a reasonable time frame. In this study the use of an artificially fissured fabric together with geotextile layers allowed for a significant magnitude of swell to be achieved within a matter of hours. Measurements of matric suction and water content throughout testing highlight the potential difficulties associated with such measurements in a fissured profile. The suction in clay along the interfaces of fissures can be significantly reduced almost instantaneously with the ingress of water. In contrast, elements closer to the centre of intact masses may take significantly longer to respond, illustrating the role of the dual processes (and hence dual scaling laws) of moisture ingress along fissures, followed by diffusion associated with swelling of the clay. A comparison of the magnitude of swell induced in this centrifuge model with that of conventional oedometer swell tests indicated gross overpredictions from the oedometer testing. In this comparison, the severe limitation of oedometer tests reducing a sample to a point of zero suction is emphasised. Finally, it is illustrated how an understanding of the rate of swell throughout an expansive profile can provide insights into the validity of the predictions from oedometer swell tests.