Influence of early diagenesis on geotechnical properties of clay sediments (Romania, Black Sea)

Type Article
Date 2018-06
Language English
Author(s) Ballas Gregory1, 2, Garziglia Sebastien1, Sultan NabilORCID1, Pelleter EwanORCID1, Toucanne SamuelORCID1, Marsset TaniaORCID1, Riboulot VincentORCID1, Ker StephanORCID1
Affiliation(s) 1 : IFREMER, Geosci Marines, BP70, F-29280 Plouzane, France.
2 : Montpellier Univ, Lab Geosci Montpellier, Campus Triolet Cc060,Pl Eugene Bataillon, F-34095 Montpellier 5, France.
Source Engineering Geology (0013-7952) (Elsevier Science Bv), 2018-06 , Vol. 240 , P. 175-188
DOI 10.1016/j.enggeo.2018.04.019
WOS© Times Cited 4
Keyword(s) Lacustrine clay sediment, Structured material, Sulfur cement, Carbonate cement, Early diagenesis, Weak layer
Abstract

The geotechnical properties of clay sediments were investigated using laboratory and in-situ measurements as part of the geohazard assessment in the Romanian sector of the Black Sea affected by landslides and seafloor deformation features. The sediments were characterized as predominantly high plastic silty clay of high compressibility, low undrained shear strength, low cohesion and moderate sensitivity. A shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction (e.g. cryptic sulfur cycle) and anaerobic oxidation of methane. Comparison of the compression behaviour of natural and reconstituted samples indicated that precipitation of these materials at particle contacts produced cementation. The analysis of deeper sediments sharing similar geochemical properties illustrated that the early precipitation of even low quantity of sulfur and carbonate cements allowed clays to develop sufficient strength to preserve an abnormal high water content even under tens of meters burial depth. Because this cementation process was observed to be associated with an enhanced sensitivity and a strain softening response to undrained shearing it was concluded that such early diagenesis should be considered as a key environmental factor, leading to weak layer formation that may influence the susceptibility of seafloor to failure.

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