Compressibility and creep of a diatomaceous soil

Abstract

Diatomaceous soils are composed by a mix of sand, fines and fossilized diatoms, which are unicellular microalgae composed by a strong silica frustule of 10 to 100 μm in size, with rough surface and enclosing a void that could give the soil a very low dry density. Due to high water storage capacity within frustules, diatomaceous soils present high Liquid Limit and classifies as high plastic silt (MH). In classical soil mechanics, low density and high plasticity are properties associated to very soft soils, however, previous studies have reported that diatomaceous soils could mobilize high shear strength and present relatively high yield stress.Due to large diversity of natural diatomaceous soils in nature, their geotechnical singularities are still not fully understood and reported data on undisturbed samples remain scarce. In this paper, a laboratory experimental study is presented on a diatomaceous soil from Mejillones Bay in northern Chile, focused on compressibility and creep. Microscopic observations and mineralogical analyses indicate that the soil contains siliceous diatom frustules of 10 to 60 μm in size, which gives the soil a very low dry density and high natural water content. Compression tests on undisturbed samples results in yield stress much higher than the overburden pressure, high contrast between compressibility before and after yielding, and significant creep strains. The diatomaceous soil does not follow empirical correlations typically used in Soil Mechanics, and is significantly more compressible than fine soils with similar geotechnical classification. Qualitative microscopic observations after compression show that a large amount of frustules have crushed, which probably explains the high compressibility of the soil.