Soil salinity assessment vii list of figures page 1 diagram of vacuum extractor apparatus for sampling soil water 8 2 a imbibition type salinity sensor with spring, housing, and pin in disassembly. The resistivity of the soil depends on the various factors likes soil composition, moisture, temperature, etc. Wenner 4 probe test is one of the most common soil resistivity testing methods. Several methods of resistivity measurement are frequently employed. Soil resistivity is a measure of how much the soil resists the flow of electricity. The most commonly used method of measuring the earth resistance of an earth electrode is the 3point measuring technique shown in figure 1. Many factors can change the resistivity measurements of soil some of which include moisture, temperature, type, and depth. Effects of soil resistivity on ground electrode resistance soil resistivity is the key factor that determines what the resistance of a grounding electrode will be, and to what depth it must be driven to obtain low ground resistance. Soil resistivity as related to underground corrosion and. The aim is to provide sufficient information to enable the user to select useful. First, data is used to make subsurface geophysical surveys as an aid in identifying ore locations, depth. Soil resistivity dial reading x multiplier range x pin spacing in feet x 191.
Typically, the lower the resistivity, the higher will be the corrosivity as indicated in the following table. A screen capture of the fourpoint probe resistivity measurement test is shown in figure 3. Sample smart ground report lightning protection by. Soil resistivity testing is the process of measuring a volume of soil to determine the conductivity of the soil. If you are involved in earthing buildings and electrical installations, here is a list of the typical soil resistivity values for different types of soil that you might encounter. For existing earth electrodes, the method involves checking. A method for measurement of soil thermal resistivity that is based on the theory that the rate of temperature rise of a line heat source is dependent upon the thermal constants of the medium in which it is placed is given. After a few moments, the resistivity reading appears, displayed in ohmmeters. Table b1 lists ranges of soil re sistivity for various types of soil. Specification for soil resistivity testing check this is the latest version before use.
The resistance of the soil between the two potential electrodes is also displayed, in ohms. This is true when discussing simple electrical design, to. Mahapatra introduction a ground water table is defined as the locus of all points in a saturated soil water system at which the pore. Apparent soil electrical conductivity measurements in agriculture. Soil resistivity the lower the resistivity the better the anode current output, less anodes to use, this is considered a prime location for a groundbed site soil moisture the soil resistivity will increase or decrease depending on the moisture content, the higher the moisture the lower the soil resistivity. Wenner method and procedure to measure soil resistivity. The resistivity of the soil varies widely throughout the world and changes seasonally. High alkalinity lowers soil resistivity and increases soil corrosivity.
Soil resistivity change in voltage change in current x pin spacing in feet x 191. In this case assume the resistance reading is 100 ohms. The most common methods of measuring the resistance of an. The connection diagram of twopole method for the soil resistance measurement. Electrical resistivity of different soil and rock types. Determining the soil resistivity to design a good substation. You are now ready to take a soil resistivity measurement. Resistivity surveys are made to satisfy the needs of two distinctly different kinds of interpretation problems. The results obtained indicated that the soil resistivity value of 488. Using the wenner method, the apparent soil resistivity value is. For measurement the user can use grounding resistance tester. Test method g57 emphasizes an in situ measurement commonly utilized in the design of a buried structures corrosion control cathodic protection systems ground bed design, and so. The soil resistivity grounding has been located on the resistance of less. In the case of the aashto standard procedure, it should be possible to use.
The objective of the soil model is to provide a good approximation of the actual soil conditions. Soil resistivity determines the flow of electric current that promotes corrosion in pipes and structural parts buried under the soil. These models are based on dielectric mixing models and treat the overall resistivity as a weighted parallel combination of the constituent resistivities. This information will enable the user to properly install and load underground cables. Soil resistivity values for different types of soil. Det4 series 4terminal earthground resistance and soil. Soil resistivity is a function of soil moisture and the concentrations of ionic soluble salts and is considered to be most comprehensive indicator of a soils corrosivity. Understanding soil resistivity testing soil resistivity measurements have a threefold purpose. The wenner method was used to measure resistivity in both locations.
First, data is used to make subsurface geophysical surveys as an aid in identifying ore locations, depth to. Soil resistivity is the property of the soil that impedes or resists the flow of electric current through it. For these reasons, the measurement of eca is among the most frequently. Factors affecting soil resistivity two samples of soil, when thoroughly dried, may in fact become very good insulators having a resistivity in excess of 109 ohmcentimeters. Standard test method for field measurement of soil. As shown in the figure, the greatest rate of change in soil resistivity is at the point where moisture in the soil freezes. Resistivity is strongly affected by the content of electrolytes in the soil, its moisture content, and even its temperature. Diagram showing four electrodes in earth constituting fourterminal.
The resistivity of soil is also affected by its temperature. The resulting soil resistivity is expressed in ohmmeter or ohmcentimeter. The wenner fourpin method, as shown in figure above, is the most commonly used technique for soil resistivity measurements. Figure b2 shows soil resistivity changes as a function of soil temperature. Second, resistivity has a direct impact on the degree of corrosion in underground pipelines. Ground metrics resistivity mapping technology overview.
The measure of the resistance offered by the soil in the flow of electricity, is called the soil resistivity. To measure the soil resistivity at a depth of three meters, we discussed a spacing between the test electrodes of nine meters. Ftn02 field thermal needle system performs accurate onsite field measurements of the thermal resistivity and thermal conductivity of soils. A practical guide to earth resistance testing weschler instruments. The measurements were used to construct a two layer soil model, given below. A method of measurement of the ground water table and soil hydraulic conductivity by don m. First, data is used to make subsurface geophysical surveys as an aid in identifying ore locations, depth to bedrock and other geological phenomena. Soil classification provides only a rough approximation.
This article describes a simple way to measure soil resistivity known as the. Why underground power cable installations need soil thermal. Soil resistivity measurements with the model 4500 given a sizable tract of land in which to determine the optimum soil re s i s t i v ity some intuition is in ord e r. Soil resistivity ground resistance 3point measurements. Earth ground resistance and resistivity sonel mru200 en 62305. Pdf in this paper, soil resistivity and ground resistance at two different sites near an electrical substation are measured using a grounding system. The wenner method uses a fourterminal earth tester, four short test spikes and connecting leads. Effects of soil resistivity on ground electrode resistance. Miller soil boxes could be used to satisfy either the astm g57 standard or the aashto t28891 standard with regard to soil sample resistivity measurements. The wenner four point method used for this investigation which was carried out on the engineering faculty complex of the delta state university, abraka, oleh campus was chosen over other methods. To measure the soil resistivity start the fluke 16252 and read the resistance value in ohms. These two tests, fourpoint probe resistivity measurement 4ptcollinear and fourpoint probe resistivity sweep 4pt resistivity sweep, can also be found in the test library and can be added to a project. However, if the earth is non homogeneous and the electrode spacing varied, a different value of resistivity.
Soil resistivity and ground resistance for dry and wet soil. Measuring soil resistivity when it is possible to choose the location of the earth connection, resistivity measurement helps to qualify the soil and thus determine the place where the soil s resistivity will be the lowest optimization of construction costs. Soil resistivity is a function of soil moisture and the concentrations of ionic soluble salts and is considered to be most comprehensive indicator of a soil s corrosivity. To do this, push the startstop button and hold it down for at least two seconds. Pdf the resistivity of soil or ground is one of the important factors to be considered when choosing for a suitable grounding spot or area. Soil resistivity testing is the single most critical factor in electrical grounding design. Soil quality varies greatly with depth and over wide areas. In this paper, soil resistivity and ground resistance at two different sites near an electrical substation are measured using a grounding system grid with and without rods. Soil resistivity measurement is an important factor in finding the best location for any grounding system. It is also part 3 in a series of short posts on soil resistivity testing methods. In this case, fluke 1625 m can be used to perform the soil resistivity measurement. The ph provides a general guide to the nature of possible corrosion. Therefore, we cannot say that any given soil has a resistivity of so many ohmcm. Resistivity is also sometimes referred to as specific resistance because, from the above formula, resistivity.
The resistivity of the soil sample is seen to change quite rapidly until approximately 20% or greater. The average soil resistivity around the plant area was also indirectly measured during the ground impedance measurements. One key determinant of a good earthing installation is the soil resistivity of the soil where the earth electrode is installed. The data soil resistivity has been analyses with soil resistivity graphic, rocks type and medium of resistance and conductance. In general, soil resistivity increases as temperature decreases. Soil resistivity and ground resistance for dry and wet. A contact soil electrical conductivity measuring system. Electrical resistivity of different soil and rock types 325 c1. The system is specifically designed for surveys that require measurements from the surface down to a depth of 1. Measurements with ftn02 comply with astm d5334 and ieee 442 standards. Some simplification to sundes procedure, shown in ieee standard 802000.
Aemc wenner soil resistivity testing explained using. Type of soil affects resistivity whether a soil is largely clay or very sandy, for example, can change the earth resistivity a great deal. Soil resistivity testing methods wenner 4 probe tester. If the lower layer contains hard and rocky layers, then their resistivity may increase with the depth. An understanding of the soil resistivity and how it varies with depth in the soil is necessary to design the grounding system in an electrical substation, or for lightning conductors. Soil electrical conductivity ec is a measurement that correlates with soil properties that affect crop productivity, including soil texture, cation exchange capacity cec, drainage conditions, organic matter level, salinity, and subsoil characteristics. Assuming that the objective is low re s i s t i v i t y, preference should be given to an ar ea containing moist loam as opposed to a.
Typically, the greater the moisture content, the lower the. Factors affecting soil resistivity test, measurement, and. Earth resistivity measurements can be used conveniently for geophysical. Wmusmru30 earthing resistance measurements with auxiliary electrodes 3lead and 4lead with auxiliary electrodes and clamp for measurement of multiple earthing systems with two clamps for measuring multiple earthing without underground edge connections. Resistivity methods environmental geophysics us epa. Pdf analysis of soil resistivity and its impact on grounding. This method is derived from the 4point method which is used for soil resistivity measurements the 3point method, called the fall of potential method, comprises the earth electrode to be measured and two other electrically independent test.
With the wenner fourpole equalmethod, the soil resistivity is measured at both selected sites, one of which contains wet soil while the other contains dry soil. Soil resistivity measurements are therefore critical for designing and constructing a grounding system appropriate for your site and requirements. Originally published in 20 and now updated in 2020. Uniform and twolayer soil models are the most commonly used soil resistivity models. Contact sensors usually measure soil electrical conductivity in two different depths, shallow 1 foot and deep 3 feet. Soil resistivity effects of soil resistivity on grounding electrode resistance soil resistivity is the key factor that determines what the resistance of a grounding electrode system will be, and to what depth it must be driven to obtain low ground resistance. Cymgrd simulation software is then used to determine the. Agricultural engineering department university of saskatchewan saskatoon, saskatchewan a. Soil resistivity and soil ph profile investigation. Pdf soil resistivity and ground resistance for dry and. Apparent soil electrical conductivity is a quick, reliable, easytotake soil measurement that often, but not always, relates to crop yield. The results obtained show how the soil resistivity varies with depth and.
The lower layers of the soil have greater moisture content and lower resistivity. Pdf effects of salt content on measurement of soil resistivity. The soil resistivity measurement methods presented so far can only be used when installing a new earth electrode. The measured soil resistivity values were then used to evaluate the ground resistance values of a grounding grid with rod for the wet soil site and without rods for the dry soil site. The resistivity of the soil sample is seen to change quite rapidly until approximately 20% or greater moisture content is reached figure 2. The soil resistivity tests were performed at a location near the plant. Pdf soil resistivity and ground resistance for dry and wet soil. Different types of soil and its characteristics have been discussed in chap. The resistivity of the soil is usually measured by the four spike methods. Soil resistivity measurements have a threefold purpose. It is a critical factor in design of systems that rely on passing current through the earths surface. Apparent soil electrical conductivity measurements in.
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