Relating the Proportion of Diatom Particles to the Physical Properties of Natural Diatomaceous Soil

Diatoms are single-celled organisms of various shapes and sizes typically found in lacustrine or marine environments. When diatoms die, the organic material decomposes, and the outer skeletons, frustules, settle and accumulate as sedimentary deposits. These soils, called diatomaceous soils, exhibit nontraditional behavior since the diatom particles are typically hollow skeletons composed of amorphous silica with intricately patterned and abrasive surfaces. Recent studies have shown that diatomaceous soils are challenging geomaterials since even a small proportion of diatom particles will notably affect engineering behavior. Furthermore, laboratory studies on diatomaceous soil mixtures have demonstrated that many engineering soil properties depend on the proportion of diatoms. For example, liquid limit and plastic limit increase as the proportion of diatom particles increases. Although the proportion of diatom particles relates to geotechnical properties, there are currently few published correlations to quantify this relationship. This research has two objectives: (1) to develop a method to characterize diatom particle proportion for natural diatomaceous soils; and (2) to investigate how these percentages relate to physical properties such as liquid limit, plastic limit, and plastic index. The soils for this project were sampled from southern and central Oregon and imaged using scanning electron microscopy (SEM) to obtain high-resolution images. These images were then analyzed using quantitative stereology to estimate diatom particle percentages. These proportions were compared to measured soil properties to evaluate the relationship for these natural diatomaceous soils. This investigation indicated that analysis of SEM images with quantitative stereology is a reasonable method to estimate the diatom proportion in soil. Additionally, the relationships between physical soil properties and diatom proportion of natural soils were reasonably consistent with the trends observed for laboratory mixtures of diatomaceous soils.