INVESTIGATION OF BURSA, ESKIKARAAGAC USING VERTICAL ELECTRICAL SOUNDING METHOD

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1 INVESTIGATION OF BURSA, ESKIKARAAGAC USING VERTICAL ELECTRICAL SOUNDING METHOD Gökçen ERYILMAZ TÜRKKAN, Serdr KORKMAZ Uludg University, Civil Engineering Deprtment, Burs, Turkey Abstrct: The im of this reserch is to study the ground resistivity of region locted t Burs, Eskikrğç villge by using verticl electricl resistivity (VES) method which is one of the geoelectricl methods. For tht purpose, two Wenner rrys were pplied on the ground. The mesured VES dt is nlyzed vi softwre nmed RES2DINV. The progrm gives lyer thicknesses nd rel resistivity vlues on two dimensionl underground resistivity sections. Interprettions on the possible loctions of wter cn lso be mde. These interprettions cn lter be verified by drilling groundwter wells. Keywords: Verticl Electricl Sounding, RES2DINV, Wenner rry Introduction Tody, climte chnge leds to shortge of wter while the demnd from limited resources increses with popultion. Drilling is unknowingly used for the purpose of serching nd finding wter. Wheres, geoelectricl methods provides some informtion bout quifer lyers nd wter existence before drilling. Geoelectricl methods re the most common methods in explortion geophysics. The method, which mkes use of the resistivity feture of erth, is used in serch for underground ssets such s wter, geotherml energy, minerls nd petrol. In this study, geophysics resistivity mesurements hve been conducted on previously chosen field over the quifer t Eskikrğç villge. Resistivity mesurement ws tken using Wenner rrys. Two pieces of Wenner rrys were mde in totl. A progrm clled RES2DINV (Loke, 2000) ws used in the evlution of these mesurements. Consequently, rel resistivity vlues nd thicknesses of geologicl lyers were obtined nd mpped in two dimensions. By considering rel resistivity vlues nd the two-dimensionl mp, inference bout wter existence ws mde. Geoelectricl Methods Bsiclly, geoelectricl methods re implemented in three different wys. These re Self Potentil (SP), Induced Polriztion (IP) nd Verticl Electricl Sounding (VES). Verticl electricl sounding method is bsed on the principle of mesuring the potentil difference formed by electric current delivered to the ground by two current electrodes. The im of this method is to determine the depth nd resistivity of underground lyers by using surfce potentil mesurements. VES method hs different geometricl rrys depending on the problem on the ground. The most common used rrys re Schlumberger, Wenner nd Dipol-Dipol. Bsic differences between rrys re investigtion depth nd horizontl solution ccurcy. Compring Wenner nd Schlumberger; both electrode rrys hve the sme current trnsmission horizontlly, however, investigtion depth is more in Schlumberger method. For the sme opening width, ccurcy of mesurement is much better in Wenner rry. According to these comprisons; generlly, Wenner is preferred for shllow studies. As to Schlumberger, it cn be used both shllow nd deep reserch (Bşokur, 2004). In Figure 1, A nd B re current, M nd N re potentil electrodes in Wenner rry. In prctice, electrode current is emitted from two points like A nd B nd then potentil difference is mesured from seprte two points like M nd N. Copyright The Online Journl of Science nd Technology 69

2 A M N B K=2 π Figure 1. Wenner rry After clculting the geometric fctor (K), pprent resistivity is clculted with Eq. 1. ρ = V I K (1) ρ= Apprent resistivity (ohm-m) V= Voltge (mv) I= Current (ma) K= Geometric fctor Essentilly, erth consists of complex structures rther thn isotropic semi-infinite medi. Becuse of this reson, resistivity reltionships do not give rel ground resistivity vlues. Resistivity vlue obtined with current given into the ground nd obtined using severl equtions is nmed s pprent resistivity. Apprent resistivity is equivlent to rel resistivity in cse of isotropic semi-infinite medi (Bşokur, 2004). To obtin rel resistivity of lyers nd thickness of lyers grphicl methods re used. Generlly, on logrithmic pper, pprent resistivity vlue is plced on verticl xis nd electrode spcing on horizontl xis nd severl methods re used to obtin vlue of rel resistivity nd thickness of lyers. These methods re given below;. Successive pproximtion methods b. Asymptotic estimte c. Rough estimte methods d. Estimte with model curves d.1. Estimte with double lyer model curves d.2. Estimte with three lyer model curves d.3. Estimte with ssistnce point crds e. Direct comment methods While Successive pproximtion methods hve been the lest used methods, Asymptotic estimte were the most used methods until computers improved (Coşkun, 2005). Progrms, such s IPI2WIN (Bobchow, 2002), RES2DINV (Loke, 1997) re widely used tody. Copyright The Online Journl of Science nd Technology 70

3 Field Study Wenner 1 Wenner 2 Figure 2. Mesuring points Wenner rrys (Multiple-electrode resistivity method) is implemented in two profiles (Figures 2-3-4). 39 electrodes were used, electrode spcing ws selected s 10 meters. Totlly, 380 meters of opening is mde for Wenner electrodes were used, electrode spcing ws selected s 10 meters. Totlly, 410 meters of opening is mde for Wenner 2. Figure 3. Wenner 1 Copyright The Online Journl of Science nd Technology 71

4 Figure 4. Wenner 2 RES2DINV s Results After records tken from multichnnel resistivity device were trnsferred to computer in DAT formt, they were evluted by RES2DINV progrm for the two Wenner rrys (Figure 5 nd Figure 6). In the evlution, rel resistivity, lyer thicknesses nd lso possible well loction were obtined. Formtions re indicted in Figure 5 nd Figure 6. Alluvil formtions re vilble in different regions in Figure 5, Figure 6. For this resons possible well loction is chosen t x=85 m long Wenner 1 rry. Alluvil formtion Metmorphic rocks Pebble Sndstone Figure 5. RES2DINV s results for Wenner 1 rry Pebble Sndstone Metmorphic rocks Alluvil formtion Figure 6. RES2DINV s results for Wenner 2 rry Copyright The Online Journl of Science nd Technology 72

5 Conclusion Considering the two-dimensionl mps in Figure 5 nd Figure 6, when resistivity vlues re smll, wter contining formtions re thought to be vilble. If the loction is indicted with blue color, it my be lluvil formtion. If the loction is indicted with yellow or green colors, it my be pebble, sndstone. Drk red unit is considered to be the metmorphic rocks. By referring to the two-dimensionl mps, comments cn be mde bout the loction of the well to be drilled. While determining the loction of well, it is necessry to consider drilling method nd formtion. The suggested well loction in this study lies long Wenner 1 line t round x=85 m which is locted wy from lluvil formtions. Mud rotry drilling method is preferred for suggested well. The reson for this method is tht it is more economicl thn others. References Bşokur, A.T. (2004), Düşey Elektrik Sondjı Verilerinin Yorumu. Ankr Üniversitesi Mühendislik Fkültesi, 225 s. Bobchow, A. (2002), "Ipi2win user s guide." Moscow Stte University. Coşkun, A. (2005), Yerltısu Kynklrının Terrmeter Ss 300C Cihzı ile Tespiti. Yüksek Lisns Tezi, Fırt Üniversitesi, Ypı Eğitimi Anbilim Dlı, Elzığ. Loke, M. H. (1997), "Res2DINV softwre user s mnul." University Sins Mlysi, Penng. Loke, M. H. (2000), Electricl Imging Surveys for Environmentl nd Engineering Studies, Prcticl Guide to 2- D nd 3-D Surveys: Mnul of RES2DINV nd RES3DINV softwre. Copyright The Online Journl of Science nd Technology 73