Microstructure of Omani expansive soils

The fundamental factors controlling the expansive nature of Omani soils are their characteristics with respect to geology, mineralogy, engineering, and microstructure. The first three factors have been extensively studied, however, the fourth has not yet been fully investigated and no work has been published on this aspect. Therefore, this paper deals with the microstructure characteristics of these soils. The scanning electron microscope was employed in this investigation. Three samples selected from different sites where expansive soils problems were known (Al-Khod, Al-Murtafa'a, and Duqm) were investigated. Two specimens from each sample, representing the vertical and horizontal planes, were tested. In addition, two samples that were subjected to swelling were tested to investigate the microfabric changes caused by swelling. The fabric of the Omani expansive soils studied generally consists of dense clay matrices, although clay-granular matrices are occasionally observed. In addition, no connectors have been observed and only few aggregations have been seen. Pore spaces are mainly of the intra-assemblage and intra-elemental types. Significant microfabric changes were induced by swelling.