Effect of intrinsic microscopic properties and suction on swell characteristics of compacted expansive clays

The complex swelling mechanism in expansive clays during moisture ingress can be succinctly explained by an examination of their core mineralogy, microfabric, grain size and suction response. This note has attempted to investigate these influential factors on five different expansive clay samples to enable further understanding of swell behaviour. Laser diffractometry tests were performed on the expansive clays to determine the clay-sized particle structure (<2 μm). One-dimensional vertical swell and swell pressure tests were carried out using the standard oedometer to establish the extent of swell. The filter paper technique was adopted to determine the matric suction values for the compacted samples. Pore sizes of the expansive clays were analytically derived and utilized to describe the swell characteristics of the clays. Further microstructural studies were conducted using the scanning electron micrograph (SEM) to better understand the pore and aggregate structure of the samples. Results of analysis of one-dimensional swell under inundation revealed an increase in swelling with increase in the montmorillonite content in the expansive clays. Swell behavioural concepts formulated to describe and predict the volume change characteristics of the clays by accounting for the clay-particle size, pore morphology and suction showed estimates of coefficient of determination exceeding 0.90 hence buttressing the critical significance of the intrinsic properties considered. This approach was tested and validated against a previous model which considered the micro-internal factors influencing swell. Very satisfactory relationships were also achieved between the inherent expansive clay properties such as plasticity index, clay activity and specific surface area.