Quantitative Models to Study the Soil Porosity

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1 Open Jounal of Moden Hydology, 016, 6, ISSN Online: ISSN Pint: Quantitative Models to Study the Soil Poosity as Function of Soil Resistivity M. Juandi Depatment of Physics Math and Science Faculty, Univesity of Riau, Pekanbau, Indonesia How to cite this pape: Juandi, M. (016) Quantitative Models to Study the Soil Poosity as Function of Soil Resistivity. Open Jounal of Moden Hydology, 6, Received: Septembe 8, 016 Accepted: Octobe 8, 016 Published: Octobe 31, 016 Copyight 016 by autho and Scientific Reseach Publishing Inc. This wok is licensed unde the Ceative Commons Attibution Intenational License (CC BY 4.0). Open Access Abstact Soil degadation is a phenomenon of land subsidence caused by humans. The pupose of this study was to detemine the quantitative models of soil poosity. The method used in this eseach was to measue gound esistance, and detemine the value of soil esistivity. Soil poosity was detemined by detemining the value of the soil volume weight, density of paticles, subsequently detemined poosity value of land. Based on the eseach, it has been found quantitative models fo the elationship between soil poosity and soil esistivity. Keywods Poosity, Resistivity, Soil 1. Intoduction Soil poosity is one facto that is vey impotant to detemine the level of soil fetility, due to the poosity facto influenced by oganic matte content, soil stuctue and soil textue [1]. The measuing method of soil poosity is commonly pefomed by a destuctive way. This method damages the sample, needs a high cost, and equies a long enough obsevation time []. Detemination of poosity by not damaging the sample becomes vey necessay; one way is to detemine the quantitative elationship between the poosity of the soil and soil esistivity [3]. Soil esistivity as physical paamete which can be detemined by means of an electic cuent in a soil sample can then be detemined the soil esistivity [4]. The patten of distibution of physical paametes such as soil esistivity and poosity can be used to illustate the quality of the land aound the campus of the Riau Univesity at Tampan Distict in Pekanbau City, Riau Povince. This mapping is vey impotant because it DOI: /ojmh Octobe 31, 016

2 can be used as data fo contolling plant gowth and potecting the envionment of the Univesity of Riau. Based on the mattes mentioned above, it would need to do eseach on the gound in the aea of the Univesity Campus Riau, Tampan Distict at Pekanbau. The pupose of this study is to detemine the quantitative model of the elationship between soil poosity and the soil esistivity. The quantitative model can be used to detemine the poosity values in the campus aea by measuing esistivity values of the Univesity Campus Riau, Tampan Distict at Pekanbau.. Theoy When two Elektoda cuents ceated by a cetain distance, such as Figue 1, the potential at the points nea the suface will be influenced by both the cuent electodes. Since the flow on both an equal and opposite electode, the potential at the point P as a esult of the cuent electode C can be witten: v 1 I ρ 1 = π so that the potential at point P1 due to the cuent electode C 1 and C ae: v I ρ v = π 11 1 Using the same way, as is shown in the Figue, the potential at P due to the cuent electode C 1 and C is, v I ρ v = π Finally the potential diffeence between P 1 and P can be witten as follows: I ρ V = π Of the magnitude of cuent and potential diffeence measued the esistivity value can be calculated using the following equation: (1) () (3) (4) v ρ = k (5) I Figue 1. Two pais of cuent and potential electodes on the suface of a homogeneous isotopic medium with esistivity ρ [7]. 54

3 whee k is a geomety facto depending on the placement of electodes on the suface. Figue 3 shows the electodes used in eseach with geomety factos with a value of k [7]: whee in AB/ = y and MN/ = x, fo y x, then Ab π π k = ( y x ) ρ = π = x MN 4 I 4 MN I MN V AB MN V In studying the methods of esistivity, should be addessed fist electical laws and egulations. One of the popeties that occued between pieces of electic chage is the chage inteactions. The magnitude of the inteaction foce between two electical chages have been investigated by Chales Augustin de Coloumb poduce: 1 Qq F = ˆ (7) 4πε 0 with is a foce vecto Coloumb, is the chage souce, is the test chage q, is the distance between the two chages, and is a constant pemittivity of vacuum FQε 0. Now the test chage q is put back into the oom, then it will be woking a style called Coloumb style, and this situation is said that the oom has an electic field Q, The electic field geneated by the chage souce is: F 1 Qq E = = ˆ (8) q 4πε 0 (6) Figue. The patten of cuent flow and equipotential field between two electodes with opposite polaity cuent [7]. Figue 3. Electodes aangement of geo-electic esistivity suvey [7]. 55

4 The electic field is a vecto quantity whose magnitude can be calculated fom the equation, wheeas if the chage Q positive diection then the diection of the electic field leave the souce, when the opposite chage Q souce is negative then the electic field diection towad the souce. Electic potential enegy of a chage is defined as the effot equied toemove the chage fom infinity to the point chage is located. 1 Qq U = F d = 4πε (9) while the electic potential (V) itself is defined as the potential enegy of unity test chage. 0 1 Q V = E d = 4πε (10) Ohm s law illustates the elationship between the amount of electic potential (V), a stong cuent (I) and the amount of esistivity o conductive R is witten as follows: V 0 = R I (11) now eview the elationship between the cuent density, electic field and the electic potential in the scala notation thus: ( J)( E)( V)V = E V I = R = R E (1) and the cuent density values obtained as follows: J = E (13) R A Magnitude is a scale that indicates the chaacteistics of a conducting mateial. This quantity is a scala quantity which is commonly efeed to as the electical conductivity of the mateial by the following equation: σ = (14) R A The unit is the I/Ohm mete. The opposite of esistivity o conductivity is commonly called the esistivity mateial by the equation: I J = σ E = E (15) ρ o, E = ρj (16) Based on Ohm s law, the elationship between the electic cuent density, the electic field and the conductivity of the medium which is expessed in the following equation: J = σ E (17) fo the electic field is a consevative field, it can be expessed in tems of potential gadient as follows: 56

5 E = V (18) if thee is no souce of the chage accumulated in the egional aea, σ V + σ V = 0 (19) fo homogeneous isotopic medium, then it is a scala constant vecto in space, so that the Equation (19) becomes: V = 0 (0) because of the symmety of the ball, potential only as a function of distance fom the souce, then obtained the following equation: dv dv = 0 (1) d d Completion of these equations can be integal o diffeential equations. By integating the two times we get, A V = + B () whee A and B integal constants whose values depend on the bounday conditions, theefoe V = 0 in the obtained B = 0, so the electic potential has a value invesely popotional to the distance fom the souce point ( ). Popeties of electicity in the soil can be classified into conduction electonically. This conduction occus when ocks o mineals have many fee electons that electic cuent ciculate in ocks o mineals by the fee electons. The flow of electicity is also influenced by the natue o chaacteistics of each ock that passed him. One of the popeties o chaacteistics of the ock is the esistivity (esistivity) that indicates the mateial s ability to conduct electicity. The geate the value of the esistivity of a mateial, the moe difficult these mateials conduct electicity and vice vesa. The esistivity has a diffeent undestanding with the esistance (esistance), wheein the esistance does not only depend on the mateial, but also depends on factos geomety o shape of the mateial, while the esistivity does not depend on the geomety facto. If the tems of a cylinde of length L, coss-sectional aea A and esistance R, the following equation obtained by Figue 4. Physically these fomulas can be intepeted if the length of the cylinde conducto (L) is aised, then the esistance will incease and if the diamete of the conducto loweed the mean coss-sectional aea (A) is educed, the esistance also inceases. Whee is the esistivity (esistivity) in ohm.m, while accoding to Ohm s law, esistivity fomulated [5]: VA ρ = (3) IL Figue 4. Cylindical conducto. 57

6 3. Method The method used in this study is an expeimental method, Tools and mateials used in this eseach that GPS, containe, soil samples, ing samples, oven, eksikato, digital scales, measuingcups, metes, pipes, calipes, battey, ammetes, voltmetes, cables, devices sufe, micosoft excel and laptops. The fist thing done is to detemine the coodinates of the point of use GPS, then do the soil sampling at a depth of 0 cm. Samples have been taken fom seveal locations then measued levels of esistivity and poosity levels ae calculated. Measuement pocedue poosity of the soil: weigh empty tube, fo example weighs Y gams, put the tube in an upight position standing on the soil suface to be measued heavy volume of soil, pess the tube slowlyso that all the tubes into the gound, lift the ja with soil, then wipe the dit on the side of the tube oute, smooth suface of the soil to the suface of both ends of the ing samples, then cove both ends of the ing with a lid, ing wee taken to the laboatoy, then dy in the oven with a tempeatue of 105 C, until its weight is constant, weigh the tube and its contents he, fo example, X-gam weight, emove the soil in the ing and calculate the dy weight of the soil by educing X with Y, Z gams weighs example, calculate the volume of soil o equal to the volume of soil, e.g. A cm 3 volume. calculate the volume weight of the soil by the fomula: weight of soil volume (ρb) = Z/A g/cm 3, detemine the moistue content of ai-dy soil to be used o the use of dy soil absolute., weigh vinomete/pumpkin Elenmeye, weigh 50 gams of dy soil absolute, and then inseted into vinomete/pumpkin Elenmeye 100 ml, fill vinomete with wate load ion o distilled wate while insing gound attached to the neck pumpkin until half-filled pumpkins, education vinomete slowly a few minutes, occasionally pumpkin shaken caefully to pevent the loss of soil along the foam, cool the flask and its contents until it eaches oom tempeatue, then add distilled wate coole that has been boiled pio to the limit volume, cap and clean the outside of the pumpkin with a dy cloth, and its contents weighed vinomete, fo example, weighs Z gams [6]. Z = Heavy soil + weight + weight of wate goud (4) Heavy wate Z pumpkin heavy heavy gound ( X) = (5) Density of wate = 1, then the weight of wate equal to the volume of wate, calculate the volume of the soil by educing the volume of the flask with a volume of wate (A). Calculate the density of paticles with the fomula: density of paticles: P = Y A (6) Poosity is calculated using Equation (7). Φ= 1 ρb ρp 100% (7) 4. Result and Discussion [ ] Based on the coelation test soil samples Region Univesity of Riau caied out in twelve points, namely, Faculty of Engineeing, Faculty of Agicultue, Faculty of Fishe- 58

7 ies, the Main Stadium, Stadium Mini, Recto UR, Rock Climbing, Natual Sciences, FEKON, FISIP, FKIP, RS UR obtained a quantitative elationship between poosity soil esistivity i.e.: Φ = 66,443ρ.068 whee (Φ) is the poosity and (ρ) is esistivity, with a coelation of 0.919, meaning that thee is a stong elationship between the esistivity with the poosity, as shown in Figue 5. Figue 5 looks the empiical elationship between poosity and esistivity in which the figue shows the elationship of poosity and soil esistivity invesely, the geate the poosity the less esistivity. Fo the pupose of mapping the esistivity values measued as much as 400 points in the campus of the Univesity of Riau, futhe mapping esistivity values in the aea of the campus of the Univesity of Riau as shown in Figue 6. Based on the distibution of esistivity values wee obtained fom 6 ohm m up to 44 ohm m, it can be said that the type of soil aea of the campus of Univesity of Riau nealy homogeneous. Fom the field obsevations that the poes in the samples can be occupied by wate, causing the value of the esistivity becomes small, geneally dominated fo a egion still closed with tees, thus inceasing the attaction between wate with soil paticles. Figue 6 shows the esistivity contous of the soil, shows the distibution of the esistivity pofile coss section of Noth-South, and shows the distibution of the esistivity pofile coss section West-East. Each is shown in Figue 7 and Figue 8. The coss-section fom noth to south shows the tend ate of esistivity deceases, but the aea aound folde units to 0.00 units evesal of the diection, that the value Figue 5. Quantitative models of soil poosity as function of soil esistivity. Figue 6. Contou soil esistivity level of 400 points in the campus of the Univesity of Riau. 59

8 of esistivity stats to ise. Fom west to east coss section showing the same tendency esistivity level, but had been a evesal, whee the esistivity values ise and fall in some aeas such as aound 0 to map units and an aea of to map units. Resistivity mapping esults in Figue 6 subsequently conveted at the ate of poosity by using a quantitative model that was obtained, as shown in Figue 6. Figue 9 is a contou level of poosity of the soil in the aea of the campus of Univesity of Riau in view two-dimensional (D). Based on Figue 6 and Figue 9, it can be Figue 7. Soil esistivity distibution pofile based on a coss-section of Noth-South. Figue 8. Soil esistivity distibution pofile based on a coss-section of West-East. Figue 9. Mapping poosity of the soil based on a quantitative model on the campus of the Univesity of Riau in Pekanbau City, Riau Povince. 60

9 said that if a lage esistivity, the poosity will be small. The highest soil poosity pecentage found in the aea of the Faculty of Economics is 63.35%, and the lowest soil poosity pecentage found in the Main Stadium is 8.66%. To some point which also has a lage poosity as FKIP 59.4%, 57.% FAPERTA, Hospital UR 53.1%, 53.1%, Faculty of Engineeing, UR Mini Stadium FAPERIKA 51.08% and 49.04% and seveal points which also has a small poosity as FMIPA 38.85%, FISIP 47.01% and Recto ate 40.89%. Figue 10 shows distibution of soil poosity in the Noth-South coss-section, and Figue 11 shows that of the West-East coss section. Figue 10 and Figue 11 ae a coss-sectional pofile to US soil poosity and BT. The coss-section fom noth to south shows the tend level of poosity is inceased, but the aea aound folde units to 0.00 units evesal diection, i.e. poosity values began to fall. Fom west to east coss section showing the same tendency poosity level, but had been a evesal in some aeas, whee poosity values fell on the aea aound 0 to map units, map units 0.00 to 0.005, to map units and ises high enough in the aea of about to 0.00 map units. Results gouping level of soil Figue 10. Soil poosity distibution pofile based on coss-section of Noth-South. Figue 11. Soil poosity distibution pofile based on coss-section of West-East. 61

10 Table 1. Results gouping level of soil quality in the campus of the Univesity of Riau based on quantitative model of the esistivity poosity. NO Poosity (%) Soil Quality Infomation Good Faculty of Engineeing 57.0 Good Faculty of Agicultue Not good Faculty of Fisheies Vey ugly Main Stadium Good Mini Stadium Not good Recto ate Good Climbing Wall Ugly FMIPA Poous Faculty of Economics Not good FISIP Good FKIP Good RS UR quality in the aea of Riau Univesity Campus based quantitative models poosity can be seen in Table Conclusion Based on the eseach that has been done, some conclusions can be dawn as follows: 1) Quantitative Models of the Soil Poosity as Function of Soil Resistivity ae fomulated as Φ = ρ.068, whee (Φ) is the poosity and (ρ) is esistivity, with a coelation of 0.919, meaning that thee is a stong elationship between the esistivity and the poosity; ) The spead of soil esistivity distibution in the aea of Riau Univesity campus at Tampan Distict fom noth to south and fom west to east has a tendency to decline, othewise the distibution of poosity level has a tendency to ise, these esults that ae in accodance with the quantitative models ae obtained. Refeences [1] Notohadipawio, T. (1998) Soil and Envionment. Diecto Geneal of Highe Education, Jakata. [] Alfi, A.M. (011) Repot of Pactical Fundamentals of Soil Science, Faculty of Agicultue. Univesity of Bengkulu. [3] Asyad, S. (000) Soil and Wate Consevation. Infomation Resouces Bogo Agicultual Institute. IPB Pess, Bogo. [4] Gant, F.S. and West, G.F. (1965) Intepetation Theoy in Applied Geophysics. McGaw- Hill Book Company, New Yok. [5] Halliday, D. and Resnick, R. (1978) Fundamentals of Physics. Cambidge Univesity Pess, New Yok, London. [6] Kossblade, L. (1989) Soil and Rock Backfill Compaction by Vibation. DRI Tanslation Katasa-Poeta, Bina Liteacy, Jakata, 111. [7] Dobin, M.B. (1981) Intoduction to Geophysical Pospecting. McGaw-Hill, New Yok. 6

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