How is the resistivity of soil determined? Used in long-distance pipelines

Conduct on-site surveys using instruments! Soil resistivity is the average value of the soil resistance per unit length, with the unit being ohms per meter. 　　Soil resistivity is a commonly used parameter in the calculations of grounding systems; it directly affects the value of the grounding resistance of the grounding device, the potential distribution across the ground grid, as well as the contact voltage and step voltage. 　　Soil resistivity is an important factor in determining the resistance of grounding electrodes. To design grounding systems properly, it is necessary to measure the soil resistivity, so that this measured value can be used as a parameter for calculating the grounding resistance. 　　One of the methods for measuring soil resistivity is to determine the grounding resistance of the grounding electrode; once this value is known, the soil resistivity can be calculated using the following formula. 　　When a steel pipe or round bar is used as the grounding electrode, ρ = 2πRjL/（ln（4L/d）） = RjL/（0.336lg（4L/d）） Ωcm. Here, L is the length of the steel pipe or round bar buried in the ground, measured in meters; d is the diameter of the steel pipe or round bar, also in meters; Rj is the measured value of the grounding resistance, in ohms. When a flat steel bar is used as the grounding electrode, ρ = 2πRjL/（ln（2L^2/(bh)）） = RjL/（0.336lg（2L^2/(bh)）） Ωcm. Here, L is the length of the flat steel bar, in meters; b is the thickness of the flat steel bar, in meters; h is the depth of burial, also in meters. 　　The aforementioned method has a drawback: due to the influence of ground resistance, significant errors can occur. If the stratification of the soil is uneven, the calculated soil resistivity also varies depending on the size of the grounding electrode and the way it is buried. Therefore, sometimes the four-stage method shown in Figure 4-27 is also used for measurement. 　　In the diagram, X and B are the current electrodes, while c and d are the voltage electrodes. The four electrodes are arranged in a straight line, and the insertion depth h of the electrodes should be less than 1/20 of the distance a between the electrodes. The soil resistivity can be calculated using the readings from the ammeter A and voltmeter V: ρ = 2πaV/I. Here, ρ represents the soil resistivity, with units of Ωcm; U is the measured voltage, in volts; I is the measured current, in amperes; and a is the distance between the electrodes, in meters. Source: http://baike.baidu.com/view/1692503.htm

Soil resistivity and its measurement in lightning protection design http://www.cnbeb.com 2006-2-24 15:16:39 I want to submit a contribution. China Building Electrical Business Network. Abstract: This article introduces the application of soil resistivity in the design of lightning protection grounding systems as well as during construction. It discusses the main factors that affect soil resistivity and the methods for measuring it. Keywords: grounding, soil resistivity, methods. In modern lightning protection engineering design, construction, and inspection, grounding is a key aspect of the work. Whether it is to protect against direct lightning strikes or induced lightning, the lightning current is ultimately directed into the ground through grounding systems. Therefore, without a proper grounding system, lightning protection cannot be achieved. And ground resistance is an important indicator that directly reflects whether the grounding condition meets the regulatory requirements. For the grounding devices of lightning protection systems, it is desirable for the grounding resistance to be as low as possible, because a lower grounding resistance leads to faster current dissipation. The higher voltage level of the object struck by lightning is maintained for a shorter period of time, which reduces the risk, and as a result, the step voltage and contact voltage also decrease. The main factors affecting the grounding resistance include soil resistivity, the size, shape, and burial depth of the grounding electrode, as well as the connection between the grounding wire and the grounding electrode. Among them, soil resistivity plays a decisive role in the magnitude of ground resistance. Therefore, before the design and construction of lightning protection projects, it is necessary to first understand the relevant information regarding the soil resistivity at the location where the grounding system will be installed, and to measure it. Therefore, understanding and mastering some of the relevant properties of soil resistivity and its measurement methods plays a decisive role in the proper design of grounding systems. 1 Main factors affecting soil resistivity Soil resistivity is one of the key factors that determine ground resistance. Ground resistance refers to the resistance encountered by current as it flows through the grounding device into the ground. In terms of numerical calculation, the grounding resistance is the ratio of the voltage between the grounding electrode of an electrical device and a point at infinity to the grounding current, that is, R = U/I, where R represents the grounding resistance. For ground resistance, the unit is . ;U; represents the grounding current, in units of A; Ie is the voltage of the grounding electrode with respect to infinity, in units of V. Soil resistivity (P+) is expressed as the soil resistance of a cube with each side measuring 10 mm. Soil resistivity varies depending on factors such as soil properties, moisture content, temperature, chemical composition, and physical properties. Therefore, when designing lightning protection systems, it is necessary to take into account the local geological conditions as well as the effects of seasons, and use the maximum value among them as the basis for the design. The main factors affecting soil resistivity are as follows. 1.1 Slope properties: Soil properties have the greatest impact on soil resistivity. Soils of different properties can have resistivity values that differ by thousands to tens of thousands of times. The soil resistivity values for different soil types are shown in the table. Note: Pi is used when it has rained heavily for several days prior to the measurement and the soil is very moist; T2 is used when the soil is moist but has a moderate water content at the time of measurement; Y3 is used when the soil is dry or when there has been little rain before the measurement. 2 Measurement of soil resistivity: In grounding technology, soil resistivity is a key technical parameter. The design of any grounding device must be based on this. This original data is required for the inspection after the completion of the grounding work, as well as for the assessment of safety once it is in operation. Therefore, at the initial design stage, once the location of the grounding device is determined, geophysical surveys for soil resistivity must be carried out; soil resistivity also needs to be measured during construction or after the system is put into operation as a means of verifying the design. Before measurement, a vertical ground electrode or a flat steel bar buried horizontally should be prepared in advance as a simulated grounding system. For example, to create a vertical ground electrode, a galvanized steel pipe with a diameter of at least 15 mm and a length of at least 1 meter can be used (the size and depth of the metal rod inserted vertically into the ground should match as closely as possible those of the individual vertical ground electrodes in the grounding system to be installed). One end of this pipe is shaped into a pointed or beveled form to facilitate its insertion into the ground at the site, after which a ground resistance tester is used to measure the ground resistance (R). The method involves setting the measurement distance between the current electrode C and the simulated ground electrode E to be S > 40 m; the voltage electrode P should be placed at the midpoint between the current electrode C and the simulated test point E. Three test electrodes are then driven into the ground respectively. During measurement, the position of the current electrode C remains unchanged; instead, the position of the voltage electrode V is moved. 3–5 points are taken within the aforementioned range, and the average of their readings is used as the measurement value (Rg). Based on the principles of electric fields, the grounding resistance of this simulated grounding electrode is known: Rg = ρ · L. After some calculations, it can be concluded that… In his book “Reflections on the Years,” Zhao Zhongxiang includes a description of the aurora borealis that caught my interest greatly: “Above the silent ice fields, the aurora borealis displays fascinating colors that seem to have a soul of their own; it moves around in a ghostly manner, its beauty unmatched by anything else in the world.” For tens of millions of years, perhaps even hundreds of millions of years, it comes here without a trace, visiting at irregular intervals; as if it were subtly winking with an enchanting gaze, showing the Antarctic ice fields a seductive smile… In Roman mythology, the aurora is called “Aurora” – she is the goddess of dawn who dispels the stars, and she is the sister of the sun god Apollo and the moon goddess Diana. In other words, Aurora was originally the name of the goddess of dawn, but now it is used to refer to the light that colors the polar night sky. As Zhao Zhongxiang described, she will forever dance in the polar night sky. In the area along the Heilongjiang River in the northern border of our country, people can often see the aurora, this colorful wonder of the night sky. The aurora is an atmospheric optical phenomenon that commonly appears in high-latitude regions, being most frequent near the North and South Poles. The one that appears in the Arctic is called the Northern Lights, while the one that appears in the Antarctic is called the Southern Lights. For thousands of years, the aurora, this strange and mysterious natural phenomenon, has held great interest for people, while also causing concern in some. Even the Inuit and Sami, who have lived in the Arctic for generations and are accustomed to seeing the auroras, feel that there is a strong sense of mystery hidden within them. We know that when solar spots and flares are active, the energy released is equivalent to the power of tens of thousands or even hundreds of thousands of nitrogen bombs exploding. The Sun emits large amounts of intense streams of charged particles, which move toward the North and South Poles along the magnetic field lines of the Earth, while also rushing into the upper layers of the Earth’s atmosphere at extremely high speeds. Due to the high speed of the charged projectile, when it collides with atoms in the air, the electrons in the outer layers of those atoms gain energy. When the energy acquired by these electrons is released and they return to their original energy level, they emit a visible beam of light – this is the aurora. The Earth is a \"large magnet.\" Charged particles are influenced by the Earth’s magnetic field, causing their flight paths to deviate toward the poles; as a result, these particles settle in the polar regions, which is why the auroras often appear in high-latitude areas. Auroras often take on various shapes such as band-like, arc-shaped, curtain-like, or radial. Due to the presence of gases such as nitrogen, oxygen, neon, etc. in the air, under the influence of charged particle streams, these various gases emit different types of light. For example, oxygen emits red light, nitrogen emits blue light, and so on; therefore, the colors of the auroras are also diverse and ever-changing. Auroras often appear suddenly, and after lasting for a while, they disappear suddenly as well. In Sweden, Norway, the former Soviet Union, and northern Canada, around 100 auroras can be seen per year, with most occurrences taking place in spring and autumn. In the Hudson Bay region of northern Canada, as many as 240 auroras can be seen each year. During periods of intense solar activity, auroras can be seen even in mid-latitude and low-latitude regions. P = 2nRg/(in4L/d). In this formula, Rg represents the measured grounding resistance of the simulated grounding electrode, in ohms; L is the length of the simulated grounding electrode buried in the ground, in meters; d is the diameter of the simulated grounding electrode, also in meters; P represents the soil resistivity, in ohm-meters. "When a flat steel bar is used as a simulated grounding electrode, the formula for calculating soil resistivity is: P = 2nRg/(inL2/hd). Here, d represents the diameter of the simulated grounding electrode or its equivalent diameter, in meters; L is the length of the flat steel bar, also in meters; and h is the distance from the midline of the flat steel bar to the ground surface. This method has been applied numerous times in practice, providing accurate data for the design of lightning protection grounding systems and for budgeting related to such projects. 3 Conclusion Before designing lightning protection systems, engineers must conduct thorough investigations, measurements, and calculations of the soil structure at the locations where grounding devices will be installed, in order to develop an accurate design plan. The soil resistivity measurement method proposed in this paper is just one of the approaches that are relatively easy to implement in engineering. In our practical work, we have applied this method multiple times for measuring soil resistivity, providing first-hand data for the proper design of lightning protection grounding systems and project budgeting. This has enhanced the reliability of the design proposals and yielded excellent results. References 1: Su Bangli, Cui Bingqiu. Published by Zhongshan University Press. Wu Wangping et al. Lightning and Lightning Protection Engineering. Guangzhou: Depth. The unit is ohms, expressed in n; 1 38 1 m; Rg represents the grounding resistance of the flat steel grounding electrode, while P is the soil resistivity, expressed in n·mo². 2: Zhang Changdong. Grounding Design, 1996. Electric World Magazine, 1996, (6).

There are various methods for measuring soil resistivity, including soil sample analysis, electromagnetic surveying, the two-pole method, the three-pole method, and the four-pole method. Among these, the four-pole method is the most ideal and commonly used approach for measuring soil resistivity. During measurement, four electrodes A, B, C, and D are first inserted into the ground at equal depths. A regulated power supply E is used to apply a current I to the outer electrodes A and B; the current flows from electrode A and returns to the power supply via electrode B. This current field generates potentials at the electrodes, and the potential difference between electrodes C and D can be measured using a potentiometer or a high-resistance voltmeter. The value of soil resistivity is directly related to the grounding resistance of the grounding system, and it is an important parameter in grounding calculations. It is also a quantity that is difficult to determine, being primarily influenced by factors such as the concentration of conductive ions in the soil, the water content in the soil, soil type, seasonal factors, temperature, and the compactness of the soil. In areas with high soil resistivity, the soil replacement method and the resistivity-reducing agent method can be used to decrease it. When using the quadrupole method to measure soil resistivity, the influence of lead mutual inductance on the measurement results must be taken into account, and the distance between the two current electrodes should generally not exceed 300 m.