Soil resistivity vs resistance in this article, we refer to both soil resistivity and soil resistance. Specification for soil resistivity testing ergon energy. In the wenner method, all four electrodes are moved for each test with the spacing between each adjacent pair remaining the same. 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. Ergon form pw000702f100 provides a record of this activity. Performing a wenner soil resistivity test with the aemc model. In such cases, the resistivity should be recorded as soil resistivity test is determined by the spacing between the four test rods which correspondingly connect to tester terminals c1, p1, p2, and c2. Factors affecting soil resistivity test, measurement, and. There are several factors which may skew the results. Test number c1 test method type a version number 3 scope the electrical conductivity indicates the amount of soluble salt ions in soil. A method of measuring earth resistivity nvlpubsnistgov.
So, soil testing should be made using the wenner 4probe method specified in ieee standard 81 part 1 or bs en7430. The most accurate of these methods is the four probe method 1 illustrated in figure 1. Our technicians perform the wenner test by lining up four equidistant electrodes in the ground and using the two outer electrodes to inject current into the soil. Safety, environmental and cultural heritage considerations the contractor shall undertake a risk assessment in accordance with ergon document pw000702r104 prior to work commencing. Following are the steps usually performed during soil resistivity testing. Next you need to decide on which test method to employ. Moisture content, temperature and salts also affect soil resistivity. Soil thermal resistivity testing is required to determine cable design and or trench design prior to cable placement.
Originally published in 20 and now updated in 2020. The resistivity of the soil varies widely throughout the world and changes seasonally. Sep 27, 2017 wenner soil resistivity testing with the aemc model 6472 in an electrical system, effective grounding ensures a safe working environment as well as proper equipment performance. The magnitude of the current also affects the resistivity of the soil. The first article discussed soil resistivity testing utilizing the 4point wenner method. Four electrode soil resistivity test method with equal probe. Before we get in to the actual test, first lets look at soil composition. Soil resistivity and soil ph profile investigation. This soil resistivity test is commonly performed at raw land sites, during the design and planning of grounding systems specific to the tested site. High alkalinity lowers soil resistivity and increases soil corrosivity. The soil resistivity test spaces four 4 probes out at equal distances to approximate the depth of the soil to be tested. Our soil resistivity test kit is designed to conveniently store and carry all of the equipment required to determine the resistivity of soil the equipment provided, when combined with a 4terminal resistance meter, such as the miller 400a or the miller 400d, is all that is necessary to perform the wenner fourpin method, as outlined in the astm g5706 standard, as well as the soilbox method. The testing procedure is limited to the wenner method of resistivity testing. Soil resistivity testing soil thermal resistivity str.
Standard test method for measurement of soil resistivity. The most reliable and widely accepted soil resistivity test in the world today is the wenner 4 point test method. One key determinant of a good earthing installation is the soil resistivity of the soil where the earth electrode is installed. Average soil resistivity for 400kv yard calculated soil resistivity in. Soil resistivity testing methods wenner 4 probe tester. It is also part 3 in a series of short posts on soil resistivity testing methods. Sp0522ver1 earth resistivity testing swp ergon energy. The ph provides a general guide to the nature of possible corrosion. Standard test method for field measurement of soil. A line traverse survey is inexpensive and easy to find differences in soil resistivity at a location and can give considerable money savings, in terms of labour and material, when trying to obtain the necessary resistance value.
The soil scientist must analyze the soil for resistivity at the given trench depth in order for the results to be considered accurate. Electrical resistivity of concrete giatec scientific inc. To accurately calculate soil resistivity, ats employs the wenner fourpin method according to astm g57. A practical guide to earth resistance testing test equipment. We test on site along a cable route and in the laboratory on full dried samples. When you perform a soil test to check for how well a grounding grid is performing or how your cathodic protection system needs to be designed, you have to spend a great deal of time and and effort doing so. This test method does not purport to address all of the safety concerns associated with its use. Soil investigation employing a new method of layervalue. Broadly speaking, earth resistance is the resistance of soil to the passage of electric.
The meter used may limit the upper range of resistivity, which can be measured. Pdf soil resistivity and ground resistance for dry and wet soil. The resistivity of the soil sample is seen to change quite rapidly until approximately 20% or greater moisture content is reached figure 2. We can also test ground or soil electrical conductivity. This manual has the current versions of our laboratory test procedures. The wenner and schlumberger test methods are both recommended, with testing and interpretation techniques summarised in the following sections. What is soil resistivity test and how is the testing done. Soil that contains 10% moisture by weight will as much as five times lower soil resistivity than that which contains 2. The soil resistivity tests were performed at a location near the plant. Our test instrument will be the aemc ground tester model. Wenner configuration method which is adopted by astm g57 was used for the. Soil test evaluation 5step testing procedure to determine if soil conditions are corrosive to cast iron soil pipe 1. The measurements were used to construct a two layer soil model, given below.
Soil resistivity testing applied technical services. Test method factors such as maximum probe depths, lengths of cables required, efficiency of the measuring technique, cost determined by the time and the size of the survey crew and ease of interpretation of the data need to be considered, when selecting the test type. Soil at room temperature will be as much as four times lower in resistivity than that at 32 degrees. Indepth descriptions of 3 soil resistivity testing techniques. How to perform the wenner fourelectrode method astm g57. Both astm g57 and ieee 81 fop are manual, handson soil resistivity testing techniques. The average soil resistivity around the plant area was also indirectly measured during the ground impedance measurements. The proposed astm test simulated expected field conditions more accurately than the aashto results also appear to indicate t 288 test.
A new procedure has been proposed that appears to more accurately simulate field conditions. Generally, testing in urban areas will only provide apparent soil resistivity values because of the influence of underground metallic plant. 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. This article describes a simple way to measure soil resistivity known as the. This edition completely replacesy 201the 9 labofebruarratory manual of test procedures. Soil resistivity is a measure of how much the soil resists or conducts electric current.
This new procedure astm c xxxxx has been extensively tested and compared with aashto t 288 in this experimental study. However, if a test was identical to an aashto, ast, or mftp procedure it was not m duplicated in this manual. This method depends on differences in the electrical resistance of different soil and rock types. 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. Understanding soil resistivity testing soil resistivity measurements have a threefold purpose. A practical guide to earth resistance testing weschler instruments. The twoelectrode soil box method is an accurate and more expeditious method than the fourpin soil box and often compliments the fourpin, in situ soil resistivity method. Type of soil soil resistivity r e earthing resistance ground electrode depth meters earthing strip meters. It takes the guesswork out of the construction and design process and always gives a predictable outcome. The earth resistivity test ert of soil was carried out at site for studies work for andhrapradesh medtech zone amtz, vishakhapatnam, andhrapradesh. M 3 6 10 5 10 20 very moist soil, swamplike 30 10 5 3 12 6 3 farming soil loamy and clay soils 100 33 17 10 40 20 10 sandy clay soil 150 50 25 15 60 30 15. Soils made up of ashes, shale or loam tend to have the lowest soil resistivity.
Aemc wenner soil resistivity testing explained using. While astm committee c09 is also developing a standard procedure for evaluating the surface electrical resistivity of concrete, the only resistivity test method that has been standardized to date is astm. Type of soil affects resistivity whether a soil is largely clay or very sandy, for example, can change the earth resistivity a great deal. The r ecommended practice is to test the soil at various depths in order to determine the be st depth for the grounding earthing electrode system. The earth resistivity field test was done in 06072017 at one location. Understanding soil resistivity testing aemc instruments.
Unless otherwise specified, the contractor shall use the wenner method four pins equally spaced. It is a critical factor in design of systems that rely on passing current through the earths surface. Wenner 4 probe test is one of the most common soil resistivity testing methods. This method is used for depth sounding the resistivity of the soil using 2 current electrodes and 2 potential electrodes. This test method is suitable only for isotropic materials. This test method is applicable for both undisturbed and remolded soil specimens and soft rock specimens. The resistivity of the soil mainly depends on its temperature. When conducting a wenner 4point soil resistivity test, we need to consider the effects that the sphereofinfluence will have on our test, in two 2 ways. Sample smart ground report lightning protection by.
It has now been about two years since the instrument was purchased during which time considerable e. Test procedure for measuring the resistivity of soil materials txdot designation. 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. To get an improved image of soil resistivity difference, it is sensible to perform a thorough survey. Soil made up of gravel, sand or stone have the highest soil resistivity. Of these two, the wenner method is the more popular and easier to use for testing soil resistivity for a grounding electrode system. Pdf resistivity is the electrical resistance between opposite faces of a unit cube of.
The soil should be wellcompacted in layers in the soil box, with air spaces eliminated as far as practicable. A proper soil resistivity test can also save valuable time and money. There are two methods that are commonly used, the wenner and the. This test requires a 3point ground resistance tester such as aemcs 4620 or 4630 ground resistance tester. The test is performed in the area where the anticipated. In such cases, the resistivity should be recorded as february 2020. As a result, indicates the soil resistivity at a depth of 6m. The pin spacings between adjacent pins need to begin at 6. Determining ph and minimum resistivity of soils and aggregates. Unless otherwise specified, the contractor shall use the wenner method four pins equally spaced for measuring soil resistivity. The distance our test is being conducted from any buried metallic objects, rail tracks, fence lines, etc. Soil resistivity values for different types of soil.
The testing instrument digital ground resistance and soil resistivity. Principle the determination of electrical conductivity ec is made with a conductivity cell by measuring the electrical resistance of a 1. This testing determines how well or how poorly the earth conducts electrical. If the magnitude of current dissipated in the soil. Therefore, we cannot say that any given soil has a resistivity of so many ohmcm. Therefore, we cannot say that any given soil has a resistivity of. The flow of current through a soil is mainly due to electrolytic action and therefore depends on the concentration of dissolved salts in the pores. First, data is used to make subsurface geophysical surveys as an aid in identifying ore locations, depth to bedrock and other geological phenomena. Second, resistivity has a direct impact on the degree of corrosion in underground pipelines. Our soil resistivity test kit is designed to conveniently store and carry all of the equipment required to determine the resistivity of soil the equipment provided, when combined with a 4terminal resistance meter, such as the miller 400a or the miller 400d, is all that is necessary to perform the wenner fourpin method, as outlined in the astm g5706 standard, as well as the soil box method. To test the conductivity of the soil in anticipation of installing a grounding system.