High Resolution Electrical Resistance Profiling of Laboratory Soil Specimens

An electrical needle-size probe is developed to effectively assess one-dimensional spatial variability of laboratory soil specimens in high resolution. A calibration procedure is also presented to determine resistance from the measured complex impedance. The capability of the developed electrical needle probes to resolve interfaces and spatial variability is explored using sand specimens prepared by various conditions. The complex impedance is measured 0.2~0.5 mm for every specimen. Results show that the coefficient of variation increases as the size of the probe reaches the size of the particle while a very large ratio of probe size to grain size would decrease the detectability of local soil variations due to averaging effects and smoothening. The attainable spatial resolution depends on the needle diameter: submillimetric resolution is typically achieved in laboratory applications and it can be scaled for field applications. The local electrical parameters permit one to infer the soil porosity and the electrolyte conductivity.

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[10] [20] [30] [40] [50] [60] 0 5 10 15 20 Depth [mm] Magnitude of impedance |Z| [k� ] (b) S = 60 % (a) S = 100 % (c) S = 30 % Fig. 5 The spatial distribution of unsaturated soils at different degrees of saturation (f = 100 kHz).