An integrated geophysical technique we proposed has begun to be utilized in the vulnerability assessment of levee systems in Japan. The integrated geophysics applies multiple methods to the same target and enables to assure to detect anomalies in the levee systems by combining individual survey results. The integrated geophysical technique mainly consists of surface wave method using Land Streamer, capacitively-coupled resistivity method using OhmMapper, and supplemental Slingram electromagnetic survey method. The geophysical properties evaluated by these methods, S-wave velocity and resistivity, are useful to evaluate permeability and stiffness of levee systems. We also demonstrated the usefulness of crossplots of the measured data to classify the target ground and to easily show vulnerable zones in the levee systems for the safety assessment. The surveyed data are correlated with ground truth data or various field test data. That is one of the reasons why we call the technique integrated. Furthermore, an appropriate geophysical technique is planned to be applied in the different phases of the safety assessment of levees, from outline survey for locating vulnerable zones to detailed survey for assessing the safety conditions of each zone. Thus far we have tested several geophysical methods at 20 actual levees in Japan, and confirmed the advantages of the above methods through the field work, in the viewpoints of cost effectiveness and their capability in detecting anomalies. We could successfully identify anomaly structures in and beneath the levee systems at excavation sites for replacing old hydraulic structures. In conclusion, the proposed integrated geophysical survey is practical and quite useful for the safety assessment of levee systems.
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