The “gray zone”: fabric and consistency of natural transitional soils

The presence of silt-size particles is believed to be one of the chief factors behind the sketchy behavior of transitional soils. Although some studies have investigated reconstituted and local silty soils on many fronts, the disproportionate understanding of the effect of the “hybrid” fabric and structure has long stood against adequate characterization of silty soils. Supported by preliminary results, this study conceptually portrays a relationship between silt’s fabric and plasticity of natural transitional soils. Close examination of scanning electron microscopy (SEM) on a few selected silty soils demonstrates their transitional particulate structure. Patterns and coverage of clay coatings qualitatively support the noted transition in the structure and consistency. The use of mean size (D_50-silt) and the mean weight diameter (MWD_silt) of the silt fraction, along with the fabric observed in micrographs, indicates a negative correlation between the coarseness of the silt-size particles and soil’s consistency. These preliminary observations further support the importance of understanding the role of silt’s fabric in transitional behavior.