The Research Of Grounding Test And Computing Method For Layered Soil

In this article, software for layered soil resistivity online monitoring system isdesigned and implemented by using Visual Basic language and SQL database. Thesoftware not only realizes the real-time data transmission, storage and display, butalso realizes the monitoring data query, statistics, analysis and printing, etc. Thesoftware makes more than one soil resistivity monitors form a monitoring network bythe serial port wire transmission mode or GPRS wireless transmission mode. Thelayered soil resistivity online monitoring system can collect within the five differentdepth levels of soil resistivity and grounding resistance in the same place by the wayof manual real-time measurement or timing measurement. This system can alsoachieve remote monitor of the change rule of multi-point soil resistivity and thegrounding resistance of radar stations on the island, communication base stations onmountain, wind turbines and such as stations under adverse conditions. In addition,through system monitoring data the following conclusions are drawn:(1) Along with the increase of soil depth, the influence of the same weather ondifferent depth soil resistivity is reduced, and the depth of20cm soil resistivity is theworst affected by the weather.(2) The time that the different depth of soil resistivity takes to meet the minimumis different, because the gap among soil particles and seepage velocity of precipitationare different in different depth of soil. The longer precipitation time and the greaterrainfall need the longer time for soil resistivity to reach the original value. And soilresistivity even cannot be recovered before the subsequent precipitation.(3) In the same condition, the grounding effect of three-dimensional groundingdevice is better and more stable than horizontal grounding device. And the groundingeffect of grounding device with low resistivity material is better and more stable thangrounding device without low resistivity material.In addition, grounding resistance of single vertical grounding electrode in frozensoil and the structure of horizontal double-layer soil and three-layer soil are simulated by using the CDEGS software in this article. Through the research finding followingconclusions:(1) The main influence factors of grounding resistance of the single verticalgrounding electrode in frozen soil include reflection coefficient, frozen soil thicknessand the length of the vertical grounding electrode.(2) When the vertical grounding electrode length less than or equal to thethickness of frozen soil, R1and R2meet a linear relationship. When the verticalgrounding electrode length is more than the thickness of frozen soil and less than orequal to the double thickness of frozen soil, R1and R2meet a nonlinear relation.(3) Compared with CDEGS simulation value, the relative error of groundingresistance from formula in this article is around±5%when the vertical groundingelectrode length less than or equal to the thickness of frozen soil. When the verticalgrounding electrode length is more than the thickness of frozen soil, the relative errorof grounding resistance is between±5%and±10%from formula in this article.(4) When soil is horizontal double-layer soil, if the resistivity of upper soil andlower soil vary widely, no matter how thick the upper soil is, if the vertical groundingelectrodes length is more than the thickness of the upper soil, the changing curve ofapparent resistivity along with the vertical grounding electrode length can be used toestimate the dividing line between upper soil and lower soil but cannot estimate thelower soil resistivity, and if the resistivity of upper soil and lower soil are similar, it ishard to estimate the dividing line between upper soil and lower soil and the soilresistivity by the changing curve of apparent resistivity along with the verticalgrounding electrode length, it need more methods such as the numerical analysis tobe used to analyze.(5) When soil is horizontal three-layer soil, the changing curve of apparentresistivity along with the vertical grounding electrode length can be used to estimatethe type of soil structure, but it is hard to estimate the dividing line between upper soiland lower soil and the soil resistivity, it need more methods such as the numericalanalysis to be used to analyze.