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| | Abstract | | Levee systems are inherently heterogeneous because they are characterized as manmade earthen structures. Underlying natural sediments are also heterogeneous in the scale of a hundred meters or shorter. Geotechnical or river engineers in Japan have divided their governing levees into segments of usually 200 m long and treated the internal structures of each segment as homogeneous. On the other hand, they have struggled to reconstruct structural conditions of levees from limited information obtained usually by visual inspection and spot geotechnical boring. It is fundamentally impossible to reconstruct a 2D or 3D structure from sparse, spot data. In contrast, geophysical techniques can provide spatially continuous profiles of physical properties of not only natural sediment layers but also artificial materials. Regretfully, the near surface geophysicists in Japan have had limited knowledge on levee systems. Accordingly, geotechnical engineers have often criticized to us that geophysical profiles were too complicated to understand and inconsistent with geotechnical information they had collected. It is crucial for the geophysicists to understand the heterogeneous structure in levee systems and to explain it properly to the geotechnical engineers. It is the key to widespread integrated geophysical investigation techniques for the safety assessment of levee systems. |
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