Impact of diatoms on fabric and chemical stability of diatom–kaolin mixtures

Abstract

Natural soils containing diatoms tend to have high compressibility, low shear strength, and difficulty of compaction. Yet, given their unique characteristics (i.e., high water absorption, liquid limit, and friction angle), there is great potential for utilizing diatoms and natural diatomaceous soils in the development of engineered particulate materials for geotechnical and geoenvironmental engineering applications. One of these applications is the use of diatom-modified soils for the construction of chemical and hydraulically-stable landfill liners and covers. Two important considerations for the long term response of liners and covers are the stability against: (1) ionic concentration-induced aggregation and (2) capillary force-induced deformations that may cause crack formation. In this study, we investigate the influence of diatomaceous earth on the resulting soil fabric and chemical stability through fabric formation studies, changes in water retention characteristics, and silica dissolution of diatomaceous earth–kaolin mixtures. Testing includes bench-scale fabric formation tests (i.e., Atterberg limits, sedimentation, and viscosity) and the measurement of water retention curves for various diatom–kaolin mixtures. The presence of diatoms (1) decreased the tendency of the mineral mixture to coagulate in the presence of salt, (2) significantly increased the liquid and plastic limits of the mineral mixture, (3) increased the water holding capacity of the mineral mixtures, and (4) reduced the solubility of kaolin mixtures, even in electrolyte solutions. That is, the presence of the diatoms has a great impact on the overall behavior of the soil mixtures by reducing the influence of pore fluid ionic concentration and by creating a stiffer skeleton that reduces the soil tendencies to deform due to osmotic and matric suction changes.