The mechanical properties of a high plasticity expansive clay

Abstract

The mechanical properties of a high plasticity expansive clay from South Africa are reported. The experimental programme considered wetting after loading tests followed by one-dimensional consolidation and unloading of undisturbed and statically compacted samples. The results of this study illustrate that laboratory preparation of expansive clays do little to alter the soil’s swell characteristics. This finding is attributed to the fact that, due to numerous swelling and shrinking cycles over a geological time frame, expansive clays tend to have reworked fabric in-situ. The effects of structure are also assessed in both undisturbed and compacted specimens by comparison of the various consolidation tests with that of a reconstituted sample. The results illustrate a gradual yielding process for both undisturbed and compacted specimens, indicating progressive disruption of structure. After consoli- dation, while the expansion indices were found to be similar for both compacted and undisturbed samples, measured values were lower than that of the reconstituted specimen. Such a result is indicative of some pres- ervation of structure after testing. It is also emphasised that consolidation tests on expansive clays are likely to exist in structure permitted space if swelling strains are restricted during the inundation process. Conversely, for most results presented it is seen that the swell caused by the inundation phase is approximately as disruptive to structure as laboratory preparation and compaction.