Electrical resistivity survey

Ground Penetrating Radar (GPR), Electromagnetic Conductivity (EM), Electrical Resistivity Surveys, or Seismic Surveys. 

The field application of electrical resistivity techniques can be affected by the presence of nearby power lines, fences, railroad tracks, and buried pipes and cables. These cultural features may create electrical interference or alter the subsurface pattern of current flow distribution. In addition, in order to complete electrical resistivity surveys you must be able to "seat" the electrodes in the ground to establish electrical continuity with the subsurface materials to be studied. 

Figure 3. Cross sectional view of electrical resistivity survey. If represents current injection electrodes, V represents electrodes used to measure resulting voltage drop.

Samouelian A, Cousin I, Tabbagh A et al (2005) Electrical resistivity survey in soil science a review. Soil Till Res 83 173-193... 

A.M. Ahmed and W.N. Sulaiman, Evaluation of Groundwater and Soil Pollution in a Landfill Area Using Electrical Resistivity Imaging Survey, Environ. Manag. 28(5), 655-663, Nov. (2001). 

Field surveys are conducted to complete either lateral profiles or vertical electrical soundings (VES). Resistivity profiles are completed by utilizing a fixed electrode spacing and obtaining an electrical resistivity value at each selected station along the... 

Inducing an electromagnetic field eliminates the need for an electrode array and, therefore, the electromagnetic field method is a more rapid tool for surveying. The elimination of electrodes to measure electrical properties of subsurface materials also enables electromagnetic surveys to be conducted in many areas where resistivity surveys cannot be considered (i.e. pavement areas, very dry sandy soils, frozen ground, railroad tracks, etc.). Electromagnetic conductivity surveys may also be used to produce rapid continuous profiles up to depths of 15 meters. 

Vertical Electrical Resistivity Sounding. The first example illustrates the ability of VES techniques to characterize regional subsurface geology into resistivity layers that have similar resistivity values at similar depths. Sediment lithologies and groundwater quality characteristics were determined for each unit based on observed resistivity values. The survey was conducted in Northampton County, Virginia which is located at the south end of the Del-Mar-Va Peninsula (9) (Figure 11). 

Electrical resistivity measurements were also taken at 28 locations selected across the site to verify the data collected by electromagnetic methods. The data obtained was in agreement with the results of the electromagnetic conductivity survey. 

The salinity may be determined directly as a total content of water-soluble salts, or as a sum of contents of particular ions. The measurement of the specific electric resistance of the soil is a very rough, but simple and rapid method. It is used for soil surveys on a wide scale. For achieving more precise results, it is possible to use a method standardized by measuring the resistance in saturated soil paste (the soil paste is prepared by mixing a soil sample with distilled water to obtain a moderately liquefied paste) and the results are corrected with respect to a temperature of 16°C. Tables are used to convert the measured electrical resistance values to the soil concentration. For more precise data, it is possible to separate the solution from the saturated soil paste and to measure the specific electric conductivity. The solution separated from the soil paste is called the saturated soil extract. 

L. A. Hall, Survey of Electrical Resistivity Measurements on 16 Pure Metals in the Temperature Range 0 to 273 K, NBS Technical Note 365,... 

The electrical resistivity method of subbottom exploration/surveying is based on the relationship/correlation between the conductivity of soils and rocks and the ion concentration in their pore waters. The resistivity is, therefore, low in saturated clays, moderate in saturated sands/granular soils, and hi in dense rocks with a few voids, little moisture, and small amount of dissolved salts. 

The resistivity method is based on the fact that any subsurface variation in conductivity alters the pattern of current flow in the ground and therefore changes the distribution of electric potential at the surface. Since the electrical resistivity of such factors as superficial deposits and bedrock differ from each other, the resistivity method may be used in their detection and to give their approximate thicknesses, relative positions and depths (Table 7.6). The first step in any resistivity survey should be to conduct a resistivity depth sounding at the site of a borehole in order to establish a correlation between resistivity and lithological layers. If a correlation cannot be established, then an alternative method is required. 

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