Four-pin method

A simple way to measure the resistivity of soil is a four-pin method in which four probes are drilled into the ground along a straight line at equal distances a and depth b. Then a voltage V is applied to the two inner probes and a current, T, is measured in the two outer probes (Figure 22.16). This test can also be conducted with the help of a ground icster as discussed in Section 22.3, which normally also has a provision for ihis test. 

Buried pipelines are subject to external corrosion from ground water and highly conductive soils. The corrosiveness of soils is often estimated based on soil resistivity measurement. The measurement is made with the Wenner four-pin method, which is used in conjunction with a Vibroground(1 and a Miller U 10-pin conductor set to determine the average electrical resistivities. A general relationship between corrosion and soil resistivity is as follows ... 

Fig. 15.8 Wenner four-pin method for measuring soii resistance.

Table 5.5 Examples of Soil Resistivity Readings Using Four-Pin Method...

The instrument is calibrated for a probe spacing of 0.3 m and gives a reading directly in ohm cm. Although this method is less accurate than the four-pin method and measures the resistivity of the soil only near the surface, it is often used for preliminary surveys, as it is quicker than the four-pin method. 

When it is impractical to make field measurements of soil resistivity, soil samples can be taken and the resistivity of the sample can be determined by using a soil box. As shown in Fig. 5.13, the method of measurement is essentially the four-pin method. Metal contacts in each end of the box pass current through the sample. 

In DC four-pin method, a direct current of 221 mA is passed between the two outer electrodes and a voltage drop of 191.8 mV is observed between the two inner electrodes. The pin spacing and anode depth is 7.5 inch. Determine the soil resistivity. 

This is the most commonly used method of measuring the soil resistance. In this method, as shown in Fig. 15.8, four pins are placed at equal distances a. A current is sent through the two outer pins (Ci and C2) [42,43]. By measuring the voltage across the two iimer pins, the soil resistance can be calculated using Ohm s law (V=IR). Soil resistance (ps) can be determined using the equation ... 

This method is based on the same principle as the Wenner four-pin test method. There are four points of electrical contact with the soil the current is driven through the two... 

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). 

Five tests on frame sub-assemblies have been conducted to study the behaviour of web cleated connections made of pultruded section. Full-size beam-to-column connections were tested to failure. Four of them were made by bolting but in one specimen bonding alone was used. The test method gave indicative results on the moment-rotation response of each connection in a frame. Results are used to provide simple design guidance for nominally pinned connections. 

Eight possible isomerizations could occur for the pinned tg + tg- conformation. Four of these isomerizations involved reorientation angles of about 67° or 113° and were consistent with the NMR data. However, each of the four motions implied a different electric dipole moment and only one of these tg + tg- to g-tg + ) was consistent with dielectric data. Therefore, from a combination of NMR data and dielectric data it was possible to uniquely determine the particular mechanism for reorientation of PVF2 although neither of these methods would determine the reorientation mechanism alone. 

Another application of solvent extraction to redox speciation studies is the method developed for iodine (Malmbeck and Skamemark 1995). It was used for online speciation of iodine in the Forsmark BWR power plant in Sweden. Iodine can enter the reactor water in two ways, either by fission of tramp uranium (uranium that is adsorbed on the outer surface of the fuel pins) or via leaking fuel pins. In this method, a tiny stream of water was withdrawn fi-om the reactor system and used as feed for a 20 stage mixer-settler battery. The mixer-settlers were arranged in four batteries with 4, 4, 6, and 6 mixer-settler units. Part of such a mixer-settler battery is shown in O Fig. 52.4. 

This paper presents die results of a calculational study of four critical experiments. The objective of the study was to calculate Keff for fast test reactor (FTR) pin arrays moderated by water and partially reflected by concrete. Calculations using the same methods for critical, water-reflected and -moderated FTR pin arrays show good agreement with experiment. However, some discrepancy is shown to exist between calculated and experimental Keff values for these four partially concrete-reflected pin arrays. 

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