Wenner technique

Figure 16.12 Scheme of the Wenner technique to determine the electrical resistivity of concrete from the surface. Spacing of the electrodes shall be larger than the maximum aggregate diameter... 

Soil resistivity can be measured by the so-called Wenner four-pin technique or, more recently, by electromagnetic measurements. The latter allows measurements in a convenient manner and at different soil depths. Another option for soil resistivity measurements is the so-called soil box method, whereby a sample is taken during excavation. Preferably sampling will be in the immediate vicinity of a buried structure (a pipe trench, for example). 

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