Soil Resistivity And Soil PH Profile Investigation: A Case Study Of .

International Journal of Scientific & Engineering Research, Volume 6, Issue 10, October-2015ISSN 2229-5518583Soil Resistivity and Soil PH ProfileInvestigation: A Case Study of Delta StateUniversity Faculty of EngineeringComplexOYUBU A.OELECTRICAL/ELECTRONIC ENGINEERING DEPARTMENT, DELTA STATE UNIVERSITY,ABRAKA, OLEH CAMPUS, NIGERIA.Emal:akposweet@yahoo.comAbstract: Electrical resistivity,the ground’s potential to pass an electrical current, is utilised in designing grounding(earthing) system for buildings, substations or specialist plants, and for measuring the corrosion susceptibility ofburied pipelines and other steel structures. Electrical resistivity is influenced by factors such as soil composition,moisture content, pore- water chemistry, presence of organic materials and chiefly soil pH. Therefore apart from thesoil’s resistivity, a knowledge of the soil’s pH, a measure of the soil’s acidity or alkalinity also becomes necessary inearthing system design. The Wenner four point method used for this investigation which was carried out on theEngineering Faculty complex of the Delta State University, Abraka, Oleh Campus was chosen over other methodsbecause it helps overcome some of the problems associated with the requirement for knowing the electrical centreof the earthing system being tested. It employs four probes (stakes) digital earth resistance meter (Tester) such asKewtech, Metrel, Metrohm, Seaward and Megger earth resistance meters (Testers) among others. Megger earthrésistance meter (Tester) was used for this investigation.IJSERKey Words: Resistivity, pH, Grounding, Wenner Four Point, Earth Resistance Meter.—————————— ——————————agricultural practice. pH indicates the acidity or the1. INTRODUCTIONalkalinitySoil resistivity, a measure of the ground’scapacity to pass an electrical current is veryfundamental to designing earthing system-a systemwhichprovides safe connectionbetweenanelectrical circuit and the ground for the dissipationof electrical faults, grounding lightning strikes andmaintaining the correct operation of electricalequipment [1]ofaparticularsoil.Experimentalevidences show that extremely high alkalinitylowers soil resistivity and increases soil corrosivitywhereas mild alkalinity withstands corrosion for alonger time. Also, soils having a pH of 5 (acidic) orbelow can lead to extreme corrosion rates andpremature pitting of metallic objects. A neutral pHof about 7 is most desirable to minimise thepotential for damage and makes earthing Rods toThe correct design of an earthing system iswithstand corrosion and carry out their protectivedependent upon the knowledge of the local ground’sfunctions on buildings/installations and appliances.resistivity. This is measured using many methodssuchastheWennerfourpoint2. LITERATURE REVIEW.method,Schlumberger Array, Driven rod (Fall of potential2.1 pHtechniques) among others.Soil PH is known as ‘soil reaction’, it is anDetermination of the local soil pH is also veryindication of the acidity or alkalinity of the soil. Soilessential to earthing system design, and othercan have a wide range of acidity, reaching anywherepurposesfrom 2.5 to 10. As pH level of 5 or below can lead torangingfromsoilcorrosivitytoIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 10, October-2015ISSN 2229-5518V Potentialextreme corrosion rate and premature pitting ofmetallic objects, a neutral pH of about 7 is ors (volts)desirable to minimise this potential for damage [2]I Currentconductors in (amperes)2.2 ResistivityR Resistance of the conductors inSoil resistivity is a critical factor in the design ofearthing system. Resistivity indicates measures howmuch the soil resists the flow of electricity.Depending on moisture, temperature and chemicalcontent, soil resistivity value can vary within wide(ohms)“Good conductors” are those with a low resistance,“Bad conductors” are those with high resistance,“Very bad conductors” are known as insulators.ranges. Typical values are;The resistance of a conductor depends on the atomicA. Usual values; from 1Ω-m to 100Ω-m.structure of the material or Resistivity (measured inohm-m or Ω-m), which is the property of a materialB. Exceptional values; from 1 Ω-m tothat measures it ability to conduct electricity. A10,000 Ω-m.material with a low resistivity will behave as aThe electrical resistivity of soil may be measured“good conductor” and one with a high resistivitywith low frequency alternating current in which thewill behave as a “bad conductor”. The commonlycurrent is applied at two locations and the potentialused symbol for resistivity is ‘ρ’ (Greek symboldifference (voltage) is measured between two points.Rho) [3].IJSERAlong this same method, direct current may beapplied in lieu of an alternating current thus causingan induced polarisation in the subsurface featureswherein the length of time the potential differencelasts after removing the current is noted for thepurpose of identifying large surface conductorsThe resistance (R) of a conductor can be derivedfrom the resistivity and vice versa as:L𝑅 ρA(2)Lρ R𝐴(3)2.3 Major concepts in measuring electricalresistivity of soil.These basic concepts are employed whenWhere ρ resistivity (Ω-m) of the materialL length of the conductordiscussing the electrical resistivity of soil:A cross sectional area (m2)Resistance is the property of a conductor whichR resistance of the material.opposes electric current flow when voltage isapplied across the two ends. It unit of measure is theohm (Ω) and the commonly used symbol is R.resistance is the ratio of the applied voltage (v) toFrom the above equations, (2) & (3), resistivity (Ωm) is the resistance between the opposite faces of acubic material with a side dimension of 1metre.the resulting current flow (I) defined by the well-Consequently, soil resistivity is the measure of theknown linear equation from ohm’s law:resistance between the opposite sides of a cube ofV I R(1)soil with a side dimension of 1metre.Resistivitytesting is therefore the process of measuring aWhere:volume of soil to determine the conductivity of soil[5]. The resulting resistivity is expressed in ohmIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 10, October-2015ISSN 2229-5518585meter (Ω-m). Soil resistivity testing is the simplelength of earth rods will stay for a longer timemost critical factor in electrical grounding design.before corrosion can occur. Same holds for otherThis is true when discussing simple electric design,metallic materials buried within this region.to dedicated low resistance or grounding systems, orto the far more complex issue involved in groundingpotential rise studies (GPR). Good soil models arethe basics of all grounding designs and they aredeveloped from accurate soil resistivity testing3. DESIGN METHODOLOGY2.4Suitablelocation fortestingelectricalThe design methodology employed in this workconductivity of soil.is broken into two sections. The first section dealsSoil electrical resistivity testing should beconducted as close to the proposed groundingsystem as possible, taking into consideration thewith the measurement using the Wenner four pointmethod, while the second section contains the soilpH profile measurement.physical terms that may cause erroneous readings.There are two issues that may cause poor qualityThe Wenner four point method uses a 4-pole groundreadings [2][3][4]:resistance meter and probes (stakes).Fortheresistivity test to be done the four probes must be1.IJSERElectrical interference causing unwantedsignal noise to enter the meter2.Metallicobjects“short-cutting”work, the probes were inserted in a straight line andtheelectrical path from probe to probe. Therule of thumb here is that a clearance equalto the stake spacing should be maintainedbetween measurement traverse and anyparallel buried metallic structures.3.inserted into the test area of the test site .In thisequally spaced. The probe, C1 was driven into theearth by the area to be measured, this area isdesignated point 0, then from that point, probes P1,P2 and C2 were driven into the earth at 5m spacingfrom each other (i.e. at 5m, 10m, 15m, respectively)from probe C1 in a straight line and at the sameTesting in the vicinity of the site inquestion is obviously important; however itmay not always be practicable. When leftwith no room or poor conditions in whichdepth of 0.5m for all probes. It is instructive to notethat while a known current is applied through theouter probes, C1 and C2, the resulting voltage ismeasured across the inner probes P1&P2.to conduct a proper soil resistivity test, oneshould use the closet available open fieldsEARTH RESISTANCEMETERwith a similar geographical soil conditionsas possible.2.5 Correlation between soil pH and soilresistivity.The pH provides a general guide to the nature ofC1possible corrosion. High alkalinity lowers soilP2P1C2GROUNDLEVEL0.5mresistivity and increases soil corrosivity. Acidic soils5m5m5mare corrosive, neutral soils are optimal.Figure 1.0: Connection for first ResistivityFrom pH chart, soil resistivity greater than 100Ωmmeasurement at 5m spacing.is slightly corrosive which indicates that buriedIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 10, October-2015ISSN 2229-5518586Ohm’s law is then applied to calculate the apparentabout 10 minutes to allow the salt inresistance:the soil to dissolve.𝐑 e.𝐕(4)𝐈The pH scan electrode was dipped intothe wet soil and the tester was turnedThe same procedure was used to calculate theon.apparent resistance for different spacing at differentlocations; each location testing was done at theseReadings were obtained for each sample afterspacing: 5m, 10m, 15m, 20m, 25m, and 30m.procedures a-eEARTH RESISTANCEMETER4. RESULTThe results obtained from the investigation areC1P2P1C2GROUNDLEVEL0.5mpresented in tables below. Table 1-4 shows theresistivity of different test locations within the testsite, while tables 5&6 show the pH values ofIJSER30m30m30mFigure 2.0: Connection for last Resistivitydifferent test locations within the test site for toplayer soil and subsoil respectively.measurement at 30m spacing.The second section of the methodology is devoted tothe soil pH measurement which was done using apH meter. A pH meter, an electronic devicemeasures the pH (acidity& alkalinity) of a liquid(solution), and sometimes semisolid substance.Special measuring probes (a glass electrodes)connected to the (electronic) meter with digitalreadout were used for the measurement. For thiswork, the measurement of pH was done as outlined:For the Wenner four point method, the resistivity iscalculated from the probe spacing and resistancegiven by the equations (5) & (6) [3] [4] [5] [6].ρ 2πawithin the test site.Where ρ resistivity in Ωmstones were excluded from the soilsample and kept in beakers.c.The beakers containing soil were filledwith distillersd.Probe (stake) spacing (m) V Voltage measured (volts)The clumps of soil were crushed andDistilled water was added to thedifferent soil samples and mixed with sspatula, shook vigorously and left forIJSER 2015http://www.ijser.org(5)(6)Loose soil samples were scoped withbeakers from different test locationsb.𝐈ρ 2πaRa a. 𝐯I Injected current (amps)R Measured resistanceTABLE 1TEST LOCATION A