Seismic methods are suitable to study the strength characteristics of dyke and dams. Seismic measurements are sensitive to density changes and compactness of soils. Therefore, areas with inadequate compactness of dykes can be detected. A correlation with SPT/CPT (Standard/Cone Penetration Testing) is often done because these methods also depend on the mechanical properties of the soil.
Example:
This example shows the result of a MASW (Multichannel Analysis of Surface Waves) measurement along a dyke in comparison to two CPT readings. The MASW procedure measures the shear wave velocity of the dyke material which enables the direct access to the material shear strength.
Result of MASW measurement
MASW array in the field
In order to ensure flooding protection the stability of dykes and dams has to be evaluated. Geophysical methods are used to locate homogeneous areas or weak points which could no longer withstand represent flooding events. A detailed geophysical investigation is usually carried out along profiles at the crest or at both sides of the dyke. The maximum exploration depth is generally below the dyke foot. Geoelectrical measurements are well suited for dyke exploration, as the good electrical conductive and sealing clayey material can be easily distinguished from sandy fillings or cavities.
Example:
The example shows the result of a geoelectrical dyke investigation on the Rhine dams. High-resistance areas are shown in red, low-resistance areas in blue colors. The sections below the electrical tomogram represent noticeable anomalies above and below the dam foot.
Geoelectrical tomogram
Geoelectrical electrodes array along the dam crest