Influence of diatom microfossils on sediment shear strength and slope stability

Abstract

Diatom microfossils have been detected in many natural marine sediment deposits around the globe and are held responsible for the disobedience to well-established geotechnical relationships between index-properties and shear strength. We revisit the static shear strength and present the first cyclic undrained shear strength experiments on diatom microfossil-clayey-silt mixtures to study the role of diatoms on submarine slope stability. It is attested that the angle of internal friction (U) increases with diatom content, however, we provide evidence for a significant overestimation of U in previous studies. Based on direct shear tests at varying normal stresses 600 kPa we find U 5 328 in contrast to 438 in pure diatom. Similarly, to static shear strength, cyclic shear strength increases with diatom content, however, in contrast to static shear strength the most drastic increase does not occur from 0% to 25% diatoms but from 75% to 100%. Interestingly, diatomaceous sediments tend to fail by liquefaction although well-established relations between index properties and liquefaction susceptibility predict the opposite. Liquefaction failure is observed solely in samples containing 50% diatoms whereas samples with lower diatom content fail by cyclic softening. We conclude diatom microfossils in marine sediments significantly contribute to an increased slope stability under static and cyclic loading conditions since diatoms lead to higher resistance independently of the loading mode. The strength increase is interpreted as a result of particle interlocking and surface roughness, which is very efficient given the highly variable habitus of diatom species.

Influence of the Diatomite Specie on the Peak and Residual Shear Strength of the Fine-Grained Soil

“…Given its morphology of hollow structure, the diatomite has a high porosity which helps it to retain a high amount of water. Other characteristics found in the literature are that they present a rough and abrasive surface, low density, large surface area, and absorbent capacity [12,13]. These singular characteristics govern the behavior of some soil deposits, leading to an increment in the void ratio and Atterberg limits but also increasing the friction angle, controverting the fundamentals established in the classic mechanical of soils.…”

What controls the remobilization and deformation of surficial sediment by seismic shaking? Linking lacustrine slope stratigraphy to great earthquakes in South–Central Chile

“…This could be due to a higher diatom content in the background sediments of lake Calafquén, illustrated by a combination of lower magnetic susceptibility and abundant bright green laminations identified as diatom blooms (Moernaut et al., 2014 ; Van Daele et al., 2015 ). Through high particle interlocking and surface roughness, sediments’ shear strength increases with diatom content (Wiemer & Kopf, 2017 ) resulting in lower erodibility and lower susceptibility to shear‐induced deformation.…”

Submarine landslide and tsunami hazards offshore southern Alaska: Seismic strengthening versus rapid sedimentation

“…The exception is that some intervals at Site 887 also contain siliceous diatom‐rich layers [ Rea et al ., ]. Recent experimental work by Wiemer and Kopf [] has shown that the presence of diatoms in sediment can result in higher shear strength relative to siliciclastic sediments. For this reason we exclude all diatom‐rich units from our analysis.…”