AN INTEGRATED STUDY OF GEOTECHNOLOGY AND SEDIMENTARY ENVIRONMENT IN BRACKISH AREAS

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This study integrates geological histories, geochemistry (sulfur, nitrogen and organic carbon concentration) and geotechnical characteristics of Holocene deposits in the Izumo Plains, southwest Japan. Total sulfur(TS), total nitrogen(TN) and total organic carbon(TOC) relationships in Holocene sediments have been used to characterize depositional environments, namely normal marine, brackish water, freshwater and euxinic sediments. The weight ratio of organic carbon to pyrite sulfur (C/S ratio) is useful for evaluating sedimentary environments. To this end, CNS elemental has led to a better understanding of sedimentary environments. The geomorphological processes of Izumo Plains with respect to sea level change during the Holocene is also described.In addition, data regarding calcite(CaCOィイD23ィエD2) content within natural silt and clay sediments with depth and its effect on strength-deformation characteristics is presented. Quantitative relationships between CaCOィイD23ィエD2 content and strength-deformation characteristics for cohesive soils of the Izumo area have been developed as a result of this work, i.e., strength-deformation characteristics increase as the CaCOィイD23ィエD2 content of the soils increases.We have attempted in this paper to demonstrate the importance of integrated studies of sedimentary environments, geotechnology, geomorphological processes during the Holocene and the usefulness of CNS elemental analysis. This study offers the designer a better understanding of mechanical behavior of Holocene deposits, leading to refinement of existing construction technology.