Mapping of quick clay by electrical resistivity tomography under structural constraint |
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| Institution: | 1. China Aero Geophysical Survey & Remote Sensing Center for Land and Resources, Beijing 100083, China;2. School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China;3. Institute of Geology, China Academy of Geological Sciences, Beijing 100037, China;1. CEDEX (CETA), C/Alfonso XII, 3 y 5, 28014 Madrid, Spain;2. Análisis y Gestión del Subsuelo S. L (AGS S.L.), c/Luxemburgo nº 4, 28224 Pozuelo de Alarcón, Madrid, Spain;3. Escuela Politécnica Superior, Universidad de Burgos, Campus La Milanera, 09001 Burgos, Spain;4. CIEMAT, Dpto de Medio Ambiente, Avda. Complutense 22, 28040 Madrid, Spain;1. Geotomo Software, 115 Cangkat Minden Jalan 5, Minden Heights, Gelugor 11700, Penang, Malaysia;2. British Geological Survey, Environmental Science Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom;3. British Geological Survey, Wallingford, Oxfordshire, OX10 8BB, United Kingdom |
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| Abstract: | Geotechnical projects usually rely on traditional sounding and drilling investigations. Drilling only provides point information and the geology needs to be interpolated between these points. Near surface geophysical methods can provide information to fill those gaps. Norwegian case studies are presented to illustrate how two-dimensional electrical resistivity tomography (ERT) can be used to accurately map the extent of quick clay deposits. Quick clay may be described as highly sensitive marine clay that changes from a relatively stiff condition to a liquid mass when disturbed. Quick clay slides present a geo-hazard and therefore layers of sensitive clay need to be mapped in detail. They are usually characterized by higher resistivity than non-sensitive clay and ERT is therefore a suitable approach to identify their occurrence. However, our experience shows that ERT cannot resolve this small resistivity contrast near large anomalies such as a bedrock interface. For this reason, a constrained inversion of ERT data was applied to delineate quick clay extent both vertically and laterally. As compared to the conventional unconstrained inversions, the constrained inversion models exhibit sharper resistivity contrasts and their resistivity values agree better with in situ measurements. |
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