Geotechnical characterization of marine sediments in the Ulleung Basin,East Sea |
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| Authors: | Changho Lee Tae Sup Yun Jong-Sub Lee Jang Jun Bahk J Carlos Santamarina |
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| Institution: | 1. Key Laboratory of Neotectonic Movement and Geohazard, Ministry of Land and Resources, Beijing 100081, China;2. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;1. IFREMER, Géosciences Marines, BP70, 29280 Plouzané, France;2. Laboratory of Géosciences Montpellier, Montpellier University, Campus Triolet cc060, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France;1. Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, Ocean University of China, Qingdao 266100, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. First Institute of Oceanography, SOA, Qingdao 266061, China;4. Qingdao Institute of Marine Geology, Ministry of Natural Resources, Qingdao 266071, China |
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| Abstract: | The geotechnical characteristics of Ulleung Basin sediments are explored using depressurized samples obtained at 2100 m water depth and 110 m below the sea floor. Geotechnical index tests, X-ray diffraction, and SEM images were obtained to identify the governing sediment parameters, chemical composition and mineralogy. We use an instrumented multi-sensor oedometer cell to determine the small-strain stiffness, zero-lateral strain compressibility and electromagnetic properties, and a triaxial device to measure shear strength. SEM images show a sediment structure dominated by microfossils, with some clay minerals that include kaolinite, illite, and chlorite. The preponderant presence of microfossils determines the high porosity of these sediments, defines their microstructure, and governs all macroscale properties. The shear wave velocity increases as the vertical effective stress increases; on the other hand, porosity, permittivity, electrical conductivity, and hydraulic conductivity decrease with increasing confinement. All these parameters exhibit a bi-linear response with effective vertical stress due to the crushable nature of microfossils. Well-established empirical correlations used to evaluate engineering parameters do not apply for these diatomaceous sediments which exhibit higher compressibility than anticipated based on correlations with index properties. Settlements will be particularly important if gas production is attempted using depressurization because this approach will cause both hydrate dissociation and increase in effective stress. |
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