éltlllHHHH H! AN EXPERIMENTAL INVESTIGATION OF BUILDING SITES Thesis. for the Degree of B. S. F. G. Dewcll K. W. Zuidema 1936 _...v u . . v. “a p F1: T .4. 1 \ x I. 1‘. . 2...? .cfiflms . . : . ,5. I. n.¢ x. ‘.' § \. “J x 3 mi“ wk“ r Wflul‘. nix . ....5.T.¥ 1"» C I. . \ n . 0."). N. or .. n. . ..'\ “’5‘ .d'fliu...‘ 1. 0 10 fr .. I. 4. .. ...l..s.;.,‘ :4. 9 5| $4.. N1 .\ t. .4». 3.111 A. la ... . . . .. m”... .\ UM. 4(— -v a“). x“ . re. WM. v .Ya‘ :|\I'..‘.7.. ‘Q‘J! \- i’gv -. 1.0.1“‘l I I i... \x .O‘.‘ 9‘ 1 o .«4... a). . ‘v 7' .o cu! . A An Experimental Investigation of Building Sites A Thesis Submitted to The Faculty of MICHIGAN STATE COLLEGE of AGRICULTURE AND APPLIED SCIENCE BY CU ." l‘ [I F GJVDehwell » Kl w.“ Zuidema Candidates for the Degree of Bachelor of Science June 1936 vurcrs‘ 103237 Data INDEX Introduction Summary History of Electrical Methods Wanner Derivation Location of plots Method Apparatus Procedure Line Electrode Level notes Plot #1 Plot #2 Columnar sections Curves Interpretation Conclusion Bibliography Page 10 13 14 17 19 21 22 28 33 34 57 38 4O We take this opportunity to express our appreciation to Hr. Keck for his assistance and advice in the course of this investigation and to the Departments of Physics and Build- ing & Grounds for the use of some of their equipment. 11 -INTRODUCTION- The survey discussed in this paper was undertaken in the hope of adding a new tool to the Civil Engineering pro- fession or perhaps, more properly, of developing an add- itional use for a recently acquired tool. Electrical meth- ods of geophysical prospecting have been applied within the last few years to the solution of certain engineering pro- blems in highway work and dam construction. The purpose of this survey was to determine the applicability of the re- sistivity method of geophysics to the investigation of the types of material to be encountered in excavation for build- ing foundations. It was believed that if some procedure could be devised for the accurate determination of subsurface conditions by such a method that it would be of considerable benefit to the engineering profession. In addition it was hoped that some knowledge might be gained that would be useful to the science of geophysics. The areas selected for the survey were proposed future building sites on the college campus, although the required depths of excavation for such buildings are so shallow as to make the value of such methods of investigation debatable. However, it was considered advisable to select actual build- ing sites since that would be one of the necessary conditions under which the method would be used. It was expected that the method would be more applicable to large buildings re- quiring at least twenty feet or more of excavation since'the increase in cost and difficulty of securing samples by boring is a.multip1e of the increase in depth. From a list of future building sites secured from the building and grounds department two were selected for in- vestigation. These two were considered by the department to be probably among the first to be constructed. A second consideration in their selection was the difference in con- ditions presented, one being only a few feet higher than the river and the other about thirty five higher. One location was on the high point between Michigan Ave. and the river west of the College Hospital. This is the site of the pro- posed new dormitory for girls. The other location was on the south side of the river, west of the Armory road and south of the baseball field. It is planned to erect a field- house on this site. ~8UMMARY- This report describes the results obtained in a survey of future campus building sites using electrical methods of geophysics. This is the first investigation, as far as is known to the authors, conducted for the purpose of applying geophysical methods to the determination of material to be encountered in shallow excavations. Geophysical methods have been applied to the investigation of subsurface con- ditions in highway and dam construction. The four electrode method of Wenner was used with mod- ified and improved type of equipment. The major improvement is the use of an auxiliary potential circuit to eliminate natural ground potentials. Current electrodes were designed which satisfy the assumption used in the derivation of wenner's formula. Results were checked with actual samples obtained by a soil auger. The effect of change in moisture content on re- sistivity readings was investigated. .mathmatioal analysis on the basis of a two layer problem was studied and found to be inadequate for the actual conditions. Tables of the results obtained at each station are in- cluded with Columnar sections for each of the two plots sur- veyed and sample resistivity curves with an explanation of interpretation. The investigation points the way to further work along the same line with this and also a second method. HISTOHY OF ELECTRICAL METHODS OF GEOPHYSICS The first investigations in electrical methods of prospecting were begun by Conrad Schlumberger of Paris, Lundberg and Nathorst of Sweden and Harry Conklin of Missouri in 1912. Other investigators have been instru- mental in futhering the development in increasing numbers. The first efforts were directed towards the determination of geologic structures particularly in the petroleum and mining fields. In recent years several investigators have extended their activities into the field of Civil Engineering. The Schlumberger Electrical Prospecting Company of New York has conducted investigations of proposed dam sites, one of which is reported by I. R. Crosby in an article in Engineering and Contracting, Vol.68 , No. 10. The U. S. Bureau of Public Roads reported the results of their studies of the application of earth resistivity methods to the problem of determining the volume of rock in highway excavations.# This report also gave a brief review of the results obtained in similar investigations by the Highway Department of Missouri. # Public Roads, Vol. 16, No. 4. June, 1955. GENERAL Electrical methods of geophysics may be divided into three classes, the Self Potential, Applied Potential and Resistivity Method. The basic principle of all of these methods is the determination of subsurface material by the study of an electrical field, either natural or applied. The variations in the electrical characteristics of dif- ferent earth materials result in disturbances of the elec- trical field and a study of these disturbances makes it possible to deduce subsurface conditions. The Potential methods have a more restricted field than the resistivity method, being particularly applic- able to the mining field. The survey described in this report was conducted by means of earth resistivity measure- ments which will be described in detail. . ’ The method used is a modification of that develOped by Gish and Rooney, based on the theory worked out by Wenner of the U. S. Bureau of Standards. The apparatus used consists of a source of current, supplied by batteries, four electrodes supplying contact to the ground, a milliammeter, potentiometer, wire and other appurtenances to complete the circuit. The following proof of Wenners' formula by Dr. L. V. King of McGill University is taken from a textbook, 'Applied Geophysics’, by Eve and Keys. In Fig. l, 01 and Cg are electrodes supplying current to the ground. P1 and P2 are potential electrodes spaced so that ClPl-P1P9=P203=A. _ Let V be the potential at any point due to current flow between 01 and C2. v must satisfy 11sz in an indefinitely extended homogeneous medium. Fige 10 At a point P distant r1 and r2 from electrodes of small dimensions (compared to r1 and r2) a solution of va-o is A B v..... ‘f e. where A and B are constants. The surface of the semi-infinite plane is easily seen to be everywhere at right angles to the equipotential surfaces. Consider electrode 01 to be a small hemisphere; then if p is the specific resistance, the normal current flow is - $.33' so that outflow of current from C1 is n - lulu dS over the electrode. D an Neglect the term E and write dSargdw, where w is a ’9 solid angle, then s - lJfli A: 2 c d 77. I p at r r dw p2 Hence A- %%.and by symmetry B: - %%T, Thus at any point V3 1.1(l'v- L). 2 1'1 1‘2 If P] and P? be electrodes so that ClPlsP1P9=P202=A, ‘ I va- R-(i- - gfi'ZA v - van 21 D ’ 2w- s~wa c-hd which is Wenner's formula. . This formula is used in the form p- El?! , where p is the resistivity, A is the electrode spacing, V is the potential and I is the current supplied. This gives the average resistivity to the depth A, the electrode spacing. This formula is based on the assumption of a homo- geneous layer of infinite extent. When this is not the case the value obtained is an average resistivity of the material. Interpretation of the results involves the use of certain emperical rules rather than a strict mathma- tical analysis, which is possible in the solution of a two layer problem, since in practice, earth presents a problem of many layers. The most general method of interpretation is by plotting the average resistivity values obtained against depth. In passing from a layer of one resistivity to another a break or change of slope will appear in the curve. The sign and magnitude of this break will depend upon the relation of the resistivities of the two layers. The depth at which this change of slope occurs will be the approximate depth of the boundary. The prominence of this break in the curve will depend also upon the thick- ness of the new bed and its depth. Thus a ten foot bed with a resistivity twice that of the overlying material will have the same effect as a.much thicker bed at greater depths. The resistivity of sands, sandstones and other dense rocks is generally much higher than that of clays, shales, etc. Thus a layer of sand underlying clay will produce a sharp rise in the resistivity curve, while the reverse condition will cause a drop in the curve. However, local conditions may affect the resistivity of a given.material frmm one area to another so that definite values of re- sistivity for the various types of material cannot be established within limits sufficiently close to render accurate quantitative determinations without additional information. 'This additional information can be secured by boring to obtain actual samples of the material en- countered below the surface in the area to be surveyed. The results from the test hole can then be correlated with the resistivity curve obtained at the same point and the information then applied to other resistivity readings taken in the area. The problem involved in resistivity surveys for the determination of geologic structures is, however, some- what different frmm that considered in this report. It consists usually of working to some definite formation which is persistent over the area in question and is of such a nature as to constitute a good electrical marker. The chief requisites of a.marker are that the bed he of considerable thickness and possess a value of resistivity differing by a ratio of five or more from the overlying formations. A sandstone formation overlain by shales constitutes such an electrical marker. The depth to this marker is obtained by readings taken at a large number of points in the region covered and then a contour map is constructed which reveals the conformation of the strata. The survey discussed in this report is concerned with material which is essentially surface soils in which a greater lateral variation is encountered than in rock for- mations. Consequently it represents a somewhat different problem which necessitates some modification of the in- terpretations if not entirely new methods of attack. LOCATION The plots selected, Fig. 2, were first measured out 150 feet square and stakes set at each corner and the mid- points. A series of levels were then run to obtain the elevation of the plots. Plot No. l, the site of the girls dormitory, was more uneven than plot No. 2, the field house site, so elevations were taken at each of the staked points. APPARATUS The instruments used were those developed by Keck and Dove as a modification of the original Gish-Rooney instru- ments. The electrical circuit is shown in Fig. 5. The purpose of each of the parts of the circuit may be more readily understood if the difficulties to be over- come in making earth resistivity measurements are first described. Natural currents are present in practically all parts of the earth which are generally quite variable. Stray currents from power lines are also of frequent oocurence. A more serious difficulty is that of polariza- tion at the electrodes. When two iron stakes are placed in the ground, a galvanic action due to the acids in the soil is set up. This creates a difference in potential between the two electrodes. These effects result in a potential reading commonly termed "ground potential" which must be eliminated from the final readings. Leakage in the instruments or 10 02 P2 Electrical Circuit. Sl K -—-+Ht Eb F180 3 Current electrodes Potential electrodes Current reversing switch Potential ' " Bucking circuit reversing switch Milliammeter Potentiometer Galvanometer Grid leak resistors Variable resistor Power Batteries Bucking " 12 wires is another source of error. Other effects which apply only to alternating current methods are induction between current and potential circuits and the skin effect due to high frequency currents. Leakage is eliminated by the use of well insulated wires and care in the prevention of dampness in the instru- ment case. The current and potential circuits should also be kept as widely separated as possible. The effect of ground potential was eliminated by Gish-Rooney method with a double commutation system. This devise reverses the direct current from the batteries at about thirty times per second as it is applied to the ground. The leads to the meters are so arranged that the current is always in the same direction. This, in effect, introduces a reversed direct current to the ground. This method usually eliminates the ground potentials but involves the use of a correction factor due to the shape of the wave. This correction factor must be determined experimentally. I The system devised by Keck and Dove uses a simple direct current and eliminates the double commutator. Ground potentials are balanced by an opposing potential supplied by an auxiliary circuit. This auxiliary circuit, which they have termed the bucking circuit, is shunted across the potential leads. It embodies a power source, one or more "B“ batteries, two resisters of the grid leak type, and a variable resistor. Rough adjustments are ob- tained by varying the auxiliary voltage applied and by 15 using grid leaks of different capacities while exact ad- Justment is secured with the variable resistor which has a range of about 50 ohms. This method enables the operator to balance out the ground potential immediately before each reading, con- stituting an accurate control particularly when the ground potential shifts slightly which is often the case. It also eliminates the necessity of a correction factor for the wave form. The instruments are mounted in a plywood cabinet with hard rubber insulation. The reversing switches are mounted on the stand which carries the batteries and instruments and provides a convenient working table in the field. The wires are carried on four reels mounted in the stand with slip rings making constant contact between the electrodes and the reversing switches. In the derivation of Wenner's formula, the current electrodes were considered as being hemispheres; this gives the proper distribution of the current so that the lines of equal potential form surfaces of concentric hemispheres. When the exploration is to go to great depths is not necessary to have hemispherical electrodes but rather a straight rod.may be used. This is possible due to the great difference in the length of the electrode and the depth of the exploration. For these depths it is not important to know the near surface conditions so the ununiformity of the potential lines may be neglected.' 14 In this experiment the depth was so shallow that it was necessary to actually get the correct distribution of potential lines, thus necessitating the use of hemispher- ical electrodes. It was impossible to actually get metal hemispheres so it was necessary to devise something that would give the same results. Two steel plates approximately six inches in diameter and one half inch thick and three and one half feet of quarter inch tool steel were obtained. A three sixteenth inch hole was drilled in the center of each plate and six others evenly spaced on a four inch circle about this center. The rod was cut into twelve ‘two and three quarters inch pieces and two three and one half inch pieces. One end of each piece was sharpened and the other and out and shaped so as to form a tight fit in the holes in the plate. The three and one half inch pins were placed in the center holes and the two and three quarter inch pins in the outside holes. The pins were securley fastened by riveting the end which protruded thru the plate. This arrangement gave the same effect as a solid hemi- sphere and made it possible to easily make a good contact with the ground. It is not necessary to have hemispherical potential electrodes since they are just to get the difference in potential between two points. Nevertheless, it was thought that by using a series of short pins closely spaced, the 15 potential lines would be intercepted as close to the sur- face as possible at a particular point and with a good contact. To accomplish this end, two ten inch, one quarter inch square brass bars were drilled with one eighth inch holes spaced at one and one half inch. One eighth inch steel pins, four and one half inches long, were sharpened on one end and the other and inserted in the holes in the bar and securely fastened with sodder. However, after a few trials using these electrodes and single three eighth inch straight rods, it was found that by inserting the single rods into ‘the ground the same distance each time the same results were obtained and the single rods were more convenient to handle. 16 The field work proceeds in the following manner. The instruments are taken to a point at which a reading is desired and connections made from the instrument to the reversing switches and batteries. The electrodes are then placed in the ground at the proper spacing for the first reading. In this case the increment of depth was taken as three feet and the first setting of electrodes was at one and one half and four and one half feet each side of the center. The line along which the electrodes are set should be selected so as to be as nearly level as possible. The potential circuit is then closed by the pushbutton to the galvanometer and the ground potential measured by the potentiometer to determine the magnitude of bucking potential required. Contact is then made to the auxiliary batteries so that an opposing potential is applied and the circuit resistances adjusted until the galvanometer reads zero. The current circuit is then closed and the galvano- meter again brought to zero with the potentiometer controls. The value of current and potential are then read on the milli- ammeter and potentiometer. By means of the reversing switches . one or more readings are taken with the current flowing in both directions. The average of these several readings are used in computing the resistivity, thus compensating for instrumental inaccuracies. The taking of readings in this manner is continued with the electrode spacing increasing by the chosen incre- l7 ment until the desired depth is reached. Thus, values of the average resistivity to each depth are obtained for the station taken. The instruments are then moved to the next station and the procedure repeated. In this survey borings were made at several of the sta- tions in order to secure samples for the correlation of read- ings. At two different stations which were taken near the beginning of the survey, readings were taken again three weeks later. Samples were obtained for each station at the same time the readings were taken and the moisture content determined. This was done to determine the effect of change in moisture content upon the resistivity readings. An attempt was made to apply a different method in obtaining the resistivity readings but insufficient work was done to make it possible to arrive at any definite conclusions. This method will be but briefly described and left with the suggestion that an investigation of its possibilities should be worthwhile. This system, which might properly be termed the line electrode method, is a further deveIOpment of the single elec- trode probe described by Eve and Keys.# The current is applied to the earth by means of two" stationary electrodes one of which is formed by a wire twice as long as the depth to be investigated, connected to the ground by pins at equal intervals. The other electrode may # Applied Geophysics, Pg. 121. 18 be placed anywhere at a distance at least ten times the depth of the probe. The pins composing the line electrode are set so as to have nearly equal contact in order that the distribu- tion of current may be uniform. This is accomplished with a resistance meter or by applying the same potential between each pin and the far electrode and adjusting the pin until the current flow is the same for each. Readings are then taken along a line at right angles to the line electrode with convenient increments. The instru- ments used and the method of reading are the same as in the Jenner method except for the manner of changing the electrodes. Fig. 4 shows a section perpendicular to the line elec- trode. Fig. 4. P1 and P2 are the potential electrodes and the resis- tivity obtained is that of a cylindrical shell of radii r1 and r2. . , Z7 E . The formula is p: -._.- 3 where E is the potential 103.5?h1 - I1 19 across 21 and P2 and I is the current per unit length of the electrode. The derivation of this formula is very simple. Assume an infinitesimal shell dr whose areaper unit length will be'fi'r; then from Ohm's Law 1 R- § and Rap - a . .2 V . . 2 9:. , 2 .. . 2 f! R [d3 J; 77_(log r2 log r1) ”log r; I r p 108 ~2 1‘1 It is obvious that the effect of the surface material is less on the deeper readings than in the Wanner method since it is a smaller percentage of the total volume. Therefore it would seem that this method should be particularly valued in a region where the resistivity of the surface material is very high. Also the distribution of current is the same for all readings taken at the same station. In the work done in this survey, considerable diff- iculty was encountered in obtaining uniform contact at the pins of the line electrode. Considering the shallow depths involved it was deemed inadvisable to permit the pins to penetrate very deeply. More investigation is indicated to perfect the technique in the use of this method. 20 Point B.M. T.Bl A-l A-Z A-3 B~1 3-2 3-3 Gul 6’2 9-3 3.15. 3.12.1 T.P.2 River (surface) Plot No.2 (center) LEVEL NOTES Plot No.1 +3 H.I. -S 9.72 867.73 4.51 4.97 868.19 10.61 5.87 3.81 8.19 4.73 4.25 10.68 6.66 5.49 Plot No.2 0.30 858.31 1.61 847.77 12.15 0.03 836.82 10.98 I 12.10 7.09 21 E137. 858.01 863.22 864.38 862.32 864.38 860.00 863.46 _ 863.96 857.51 861.63 863.96 858.01 846.16 836.79 824.72 829.73 Depth ft. Depth ft. PLOT No.1 22 DATA A-l Current Potential amps. volts. .0830 .7060 .0638 .2250 .0694 .1717 .0900 .1766 .059‘ .1084 .0637 .1053 .0780 .1223 .0778 .1171 .0860 .1265 .0600 .0843 A-2 Current Potential amps. volts. .0850 .5785 .0940 .2980 .0859 .1975 .0534 .0958 .0500 .0783 .0480 ,0577 .0550 .0700 .0720 .0859 ~0706 .0880 .0740 .0812 Resistivity Ohms /0 ll. ft. 160 Resistivity ohms/cu.ft. 128 119 207 Depth ft. Depth ft. 12 15 18 21 27 30 80 90 100 Current amps. .0410 .0416 .0410 .0485 .0451 .0420 .0480 .0410 .0383 Current amps. .0800 .0680 .0785 .0717 .0589 .0757 .0649 .0629 .0642 .0555 .0543 .0899 .0893 A-3 (rain) 6-1 we- {,1 Potential volts .2854 .1456 .1034 .0930 .0776 .0635 .0677 .0510 .0441 Potential volts Resistivity ohms/cu.ft. 131 132 143 149 162 171 183 188 196 Resistivity ohms/cu.ft. 117 128 Depth ft. (n O; 12 15 18 21 27 30 Depth ft. 12 15 18 21 24 27 30 Current amps. .0640 .0610 .0613 .0604 .0697 .0658 Current amps. .0620 .0570 .0690 .0590 .0493 .0430 .0480 .0475 .0540 .0600 G—2 Potential G-3 Potential 24 volts .5874 .2714 .1743 .1339 .1260 .1065 .0783 .0878 .0708 .0760 volts .4915 .1940 .1558 .1035 .0762 .0592 .0625 .0601 .0658 .0720 Resistivity ohms/ou.ft. Resistivity ohms/cu.ft. 149 129 128 132 146 155 172 191 210 226 D-1 Trial 1 Depth Current Potential Resistivity %IMoisture ft.’ amps. volts ohms/cu.ft. 5 .2840 1.5465 105 21.65 6 .2675 .8515 120 18.95 9 .2050 .5515 152 16.65 12 .2055 .4550 161 11.29 15 .2050 .5892 178 18 .0955 .1564 189 9.48 21 .0705 .1110 208 24 .0940 .1415 227 27 .0860 .1278 252 50 .0750 .10498 271 Trial 2 Depth Current Potential Resistivity % moisture ft. amps. volts ohms/cu.ft. 3 .0639 .5232 95 17.90 5 ~0625 .2014 121 12.70 9 .0495 .1165 135 17.00 12 .0430 .0858 150 21.25 15 o0465 .0803 165 18.10 18 .0975 .1509 186 10.57 21 .0983 .1495 201 24 .0505 .0743 222 27 .0590 .0540 255 50 .0285 .0587 256 25 D-2 26 Trial 1 Depth Current Potential Resistivity Moisture ft. amps. volts ohms/cu.ft. 3 .0646 .4297 125 20.90 6 .0620 .2267 138 15.00 9 .0610 .1581 147 15.50 12 .0710 .1523 162 16.50 15 .0862 .1591 174 17.60 18 .0676 .1101 185 20.30 21 .0788 .1177 197 9.10 24 .0801 .1120 211 12.80 27 .0695 .0941 230 8.70 30 .0620 .0817 242 Trial 2 Depth Current Potential Resistivity Moisture ft. amps. volts ohms/cu.ft. 3 .0677 .3937 110 7.85 6 .0765 .2424 120 7.90 9 .0780 ,1808 131 8.00 12 .0768 .1445 142 8.15 15 .0835 .1400 158 8.00 18 .0358 .1295 171 7.95 21 ,0875 .1222 184 24 .0485 .0640 199 27 .0495 .0657 218 50 .0405 .0497 251 Depth ft. 12 15 18 21 27 30 Current amps. .0660 .0680 .0639 .0500 .0478 .0580 .0574 .0583 .0555 .0575 D-3 Potential volts .8294 .3229 .1881 .1085 .0777 .0812 .0709 .0682 .0623 .0622 27 Resistivity ohms/cu.ft. 237 178 167 164 153 158 163 176 190 204 , in»... iir~..wrnll..w..vl.b. qua $.35... it)“. . a Depth ft. 12 15 18 21 24 27 50 12 15 18 21 24 27 30 Current amps. .0614 .0643 .0681 .0661 .0597 .0570 .0555 .0449 .0535 .0520 .0609 .0540 .0497 .0608 .0661 .0619 .0625 .0614 .0649 .0697 Plot No. 2 A-1 Potential A-2 volts .7920 .4461 .3109 .2324 .1700 .1371 .1118 .0778 .0785 .0660 .9256 .4466 .2467 .2150 .1887 .1451 .1238 .1070 .0980 .0924 28 Resistivity Ohms [cuefto 243 262 258 265 269 272 266 261 249 239 286 311 281 267 268 266 262 262 256 250 HIS.“ Depth ft. 12 15 18 21 24 27 12 15 18 21 24 27 30 ' Current amps. .0764 .0789 .0735 .0832 .0852 .0740 .0772 .0659 .0750 .0725 .0875 .0830 .0900 .0840 .0760 .0850 .0780 .0830 .0850 .0800 A-3 B-l Potential volts 1.1660 .5629 .3288 .2783 .2346 .1695 .1504 .1157 .1131 .0968 I 1.0180 29 .5764 .4139 .2767 .1903 .1693 .1360 .1270 .1131 .0978 Resistivity Ohms [Cuofto 288 269 263 252 260 259 257 264 257 252 220 261 260 249 236‘ 250 250 251 251 - 251 ~ , “If-fill. 1.!» III. IE“I’P m...r>..n~.r Kali-.4 . T v. u . . cu Depth ft.’ 12 15 18 21 24 27 3O 12 15 '18 21 27 30 Current amps. .0581 .0654 .0675 .0640 .0838 .0794 .0778 .0698 .0739 .0766 .0270 .0645 .0600 .0660 .0645 .0625 .0670 .0665 .0605 .0600 B-2 Potential volts .7660 .4296 .3116 .2196 .1731 .1769 .1486 .1094 .1007 .0949 .5309 .3248 .2186 .1970 .1760 .1496 .1415 .1267 .1054 .0930 Resistivity 0111118 [$211.13. 248 247 260 258 256 252 252 237 231 233 176 190 207 225 257 271 279 287 296 293 Depth ft. 3 6 9 12 15 18 21 24 27 30 12 15 18 21 24 27 30 Current amps. .0540 .0508 .0515 .0596 .0560 .0553 .0527 .0520 .0479 .0503 .0758 .0619 .0598 .0619 .0568 .0672 .0660 .0741 .0790 .0740 0-1 Potential 31 volts .7143 .3423 .2172 .1976 .1506 .1310 .1117 .0989 .0848 .0813 .8448 .3575 .2449 .1995 .1616 .1680 .1473 .1479 .1423 .1193 Resistivity chins /ou.ft. 249 254 239 250 254 268 279 287 300 304 206 218 231 243 268 284 295 302 306 304 Depth It. 12 15 18 24 27 30 Current amps. .0512 .0460 .0611 .0816 .0878 .0818 .0974 .0550 .0424 .0657 0-3 Potential volts. 32 1.0823 .4449 .3228 .2854 .2364 .1750 .1775 .0882 .0607 .0812 Resistivity ohms lou.ft. 399 373 299 264 248 242 241 241 243 233 . on: In. E! "In." 1. - i'I I c I . mlll III .II II_III1I 'lllllll'll'l' II I 5 .54 II 1 I ll'll'fllll ll llll'l'lll I'IIII 5'55'QI I. QIOIII I'll ! . . 1.. ; . . I .. _ v .I .l ., O I. . I _ U . u _ _. _ I. . . _ I. I I .I m . I _ I . _ . , .. . . .. . _ . . . l. — III “”1 I v . . u I... .0 I . All. ,III — . II I. I “I: . -|.lr 0| In I. O I I 1.0.1.5 — I I I 7 . 1.. II m. I III.I ” . I I .. ... __ . .. . ___ ; __.. __ . .2 n _._ . _. .__ _ I :1 .0 _. .. . . I.... .o».. _. . . . l_ 1., I __ 11 ._ . .. .. u 1. ...__ . o v Lll‘r 5.7 lllll 4r"- III In‘ . I. II I - I- I 'I lll'll'llul- ‘11 J5 tilhlli'fl'1l1J'Jl I'I_Il|.l 55_II_ II'IIII IfIl.‘ ill‘l'd‘ '7'. II 5. llll _' 5 I I I'll. .i'll 'Illl I . |ll III. -l I: . _ - I| . ,. . . . .| r . I, . . I J I - _- I _.. . .. . . ,.. -. — .._+_m—. — .— . . .— . ._.., m 1... .u ‘ ._. .1 . ._._ I — . . _ __ u I _ — — _ I _ 1v . .I . ‘I 1 .U .. — . I I. _ . F .u II V ..I _ A.- . I O . I .. — _ . r a. + _ . -. - . . 1 i . . . _ _ .. o . I ‘I .. . I 1 J. i _ _ - o — I I l l 1 --'.-a--:. 44+- stifi "'1 . «1. .p1f-_ .8886. . 5-.II‘III..."—O— - -- . Jesi ." ‘- l 1 A; ‘l-— .1 I I “I A ' C1111 ‘——— ‘ II— I I 1—- l y— L ( |F~—‘ - r I r1 J L 3 THE B COL-I 00.. COLUMBI'S. OHIO. In T-flo-l' - _ — .h. . .I I I Q I- u _I I III I a I - 0' l I I _ w? _ I V. _ . I. — I. I I I . _ . I I I I o I. 0 I I I ..l. -_ — _.III .I __...I — . I..I _ no 1 I. .0. . —. ”IllIllILIIIII-IIIIIIIIHI IIIOIIIIII IIIlIIIII I II I O III-II III II I I1II I III . .. .IIOI - C I _ I I - , I. . n .. .. I .4 VII I J .I‘.‘ .I -I.‘ I I I ' _ I t a I. — . I . . .l .. . v 0 I l I . I o I III I I. t“ ~.I£H.I..nu.....|r i .1 _. .w... .1... LI-.. .‘I ‘ _. . . - . .- III I'III II. I I......._.III.I _.I_... ...I..u..II I..- i . .I._......- m. | ll 'JIIII II I «I I I J I I ! II I I Al -—_—- - — m I! COL! 00.. COLI'IBUS. 0310. ’0. T—M. II I . i .v. . I . . . .. .-.. .. . I I... -. . ......»hIII... ..I ..I“ . .I I I . III ’ITI III...‘-IQI III III! .IIIH.I....II. III. MIMI ILMI.'.I.II.IU.II .II .1 . I. b ..I‘.. “I I I III: I I“ Ir! I. ..I. .. IIII. . ‘II‘Iu c (I.IIIOIIIII-4“> 'IINJIIIIIIIIJIIIIIIIIIII III-2.1.3 E III J‘I—II III “III I.I I “I I .,I._.I .. .I .. M .. v I I {all . '1: w J “ I|Hl.4|111.i1. I . . 1 m . 1.1 I ~ . I . . I .I _. .... ..I _..-.. . . . ._ I I _ ... I. . .I II . ..I l . _u! I.I I I .. _ _ . _ ._ II . .. . . . M . __ . o . .II II — ..I. III” I * ll..|.tOIlII.I.— III I I O I I .m} I I ... .I. I III M II ”I. I I II I” .I II u I.I. III- .I I II Pl I D . . .. .. . .M... -. .. n + ..M . _ - . I . I I .. . . . _ I . I m. . I. m .. u —4 I W t C O .. I — I I . . . I I _ . _ ._ I . . .... a: I I , I I’ll-III. I.I.I WTIIIIIII IIHI. I} 1.: III .IIIIIIIIII+I ..I-II. I. ..I I I I all- In] 11‘ Ir. I I“... .1. III ITII‘IIII '11.. I III! IIJIIOIII I II III-III III. III L I ..I-..I . I. . .— . . . ..i .I.. 0, . I I ... &.:— I I _.. .. I — I _ I I I .I I . - n | . .I I ....1 I I. w. II“. I I I LI \ ”I .I. I I _ . - _. . . . _ __ . . ._ ._ . . .- _ . -. I. .. . . L ”flow _nlfilflfl, I.I. .I.. I VI “..I. I O .0: I 1.. II... T .I ..I“: IIIII ,. .. A. III. III. IIIIIva .I.-III IIIIII IIIIOI .. III. .III I . III _....110 ii I. I m I- I.I I II IIII u. I. —. I . .m . u ..I. .0-.. .W . II InI .I. I. I .n . _ ... . . I I . I "...I n r . .fi I .I I — . .. I .I .I . I, I . . . .. I . . l. . _. ....l+ .I .. u I .I.».Iw J . — ~II . II. I . * . uh . .. . . I _ l. 4.1 .0 II ..I n m u H MI .I. — IIIIF+FIII+QWIIIIIIIIIQfl1IIII JIIIIIIWIIIIIJIIHII IOIOIOIIIIQII. III, II'I1II I I 0 IIIIII ITIIFIIII rIIIFrI IllIl. III+ III III I‘ll-VIII I . I . . ,L I I T. ..., In. x - I. I , I _ . II ” I n 0 _ u . I __ flI... . u I" I IM IM _... III“ I I u I ”M 0 U7 l I.- ...I I w .......T I I .I. - . I .. I M. ...I . I . I I I. . .... MI” _M..I-.M w I. M. ....-. M ._ .. M .. M ..I . . ... M . M . ..- M . III! I OI .1 I a I IIIII. III. II III I... I In 0-4! I.J.I I.I.) III II..- I. lull. III .III I I... I III! I I I .9... I It III .Ir I ‘M H. t — . I . I I ., n II. ..I. I III . I0 . I I II I I I. I I I .-. I. ,. I I ... . _ . . I. I o v. ..I... .I.. .I M .1..|.._ _ 1 ml .I. ..1... .. I . II I I _ . I.__ ...I .I.“. I . u . .. , _..I. . I- _.I I... VI ...“. . . In; ..II.I.M.I11..I I.I ...n .. I 1.. ...I II. .M.* .. _ I IIIIII 'rrcli...l..lIl fVIOiWIIII . .IIIMIJJIII-II IIIIPIOII 10 ..IIIIII {0% 1L 1 I» IIILIJF I _..... I I III I'll-.IIIIIIIIIII ..I ,. . I I. 1 I . .. . . ., I . .I — .I I .I 0 fl II. I III II”. n .I 41 I ..I I I HID ... _.. .. ..I... . ... . . .... I... r -.. .% MCI. . . . I I» ... - _. . . I.I II...— .. . I ._. I . I. — ..I I r. I I... . J. I ...I. I . —«. I %. III. I H .I l . I I . . I . IQfi . I I ..., I . M II II .II. I. ..I . ,..r , III I v .I. I I I.‘ 'I ._ 1 I.I I .III —II.I OI I..IIIII ..I I. IJII .I III I .I.. .IIIIIIIIII .III I II I II. II. ..I III rl III IIIIII I | I." I 'I I I II I .M I . II ...- V. v4 .. ..I I _. I I .I. I. _I .. . . II In. a 4 o I ‘ :— .. . . I I .. I .. . I . r I _ I. v . : _ ._. Q. . | .. J . fiI I O I I L . F (II M - I . I .o I I .... I . .. ..or I IIM I I . I, I_ . a ... . i o O .... . . _. . . IM .3 . - . _T I. .I.. . H. -. .- . ..- .. v TIIIIIITIIIIIIICIIOIZIIIIIIIIII. II. III. II II I III I. I [I.I-III... fill-I.I I'll-I‘ll! III? I11 PIIrr III J. F «ll I III! 1 III III IT I I III II III III-I.I II VI I. ,. . . . I I I ..1 .I M “I... .IWI.I .uM W . I #. 1.4...J. I . MM . I — ... I. .4 . I. M. . _. .. . M . -M. -. _- . n. .- .. I... . .. _ . .. L _I.,. II I .IH. I I II _.. I . . m ..I — F0 ,__ UI _ I I. h I _ III—a! I II —I | 4.! I . I I II I I I I III F I "I I III III...”— II*.. IOI1I'II III... III II?# III—IIIM ulIIfl OLHIIO I I . — ¢ 0 L . “I I . .. I . I I. I . I , . .1 I. I _.. . I .m w ___..,..~ ...u I — I. H I fl I ".I. —. .I . __ I I 1 I. I. . . I O . . . I I .I . I . . .I . .IIIILIIIIIrI-TIIII I. .I P I .II. I .T II... . III I III! III. I “I VJ.” JP]. I. III II .IIIIIIIVIIIII I.IIrII J. -.I1I IIIIII¢IOIFIIIIIYFII imllI-MLI l. -TI III-III. .IIIIHIIIYOIPIIII I. . I.. _ - I I . . _ I . I . .p M... I I . w I I .. . I . y. . I .I _..- . I ..-”. . a — .- l - O 'I l ‘ __M p V. n I I II . II V - L . - . I - . .- 1 9. ~. I . I I II I III- ..I- III? . I.IIIIII. I.III ‘II * III 9 I ' . I I. I II .I.; I I . Lvl I II ...I. ..I III“ .0 II.I...I II. N 4 . _ . . I I. I.. . . . _. .. I I . I» III I . I .u- I _. . o . .. . .II'wI .- w . .. .. s . — I I Til. I+M . (I I. _ .. I . . I . I I I I I a. , I I I I I . I . In . II. M I: . I I _I . I -. — I a , I I I I. _ x .. I I . .> .I.: . .. I .. . . . _ I. , I . I Y} I I.I! mII ... zlfi '- I I I“ III» I I_OI III "I .I.!” 4 M. I q I OIJIIII. TI'OOIIILrIIIIIIIOI Ill-I“ III-”III.- fIIIIII'I-II Ill "II-IIIIIII F I.IIIII I III L I I .7 ... _ I .. .. . M a . Y . , . . 1 . n ll ... I I I .- . _ I T I , I -. . . I | . .-. . . . .. .. ._ _. . . . . .. _. _... wl _ . . _ . I I M. . I I q I I .r .I . _ I — . . . — I VII. 01-. C. .I— _ 0 0|. D I. r O I 9 III; 0' IF. I I III. I '0. II .III II II I II I II I r .I.! . L._ I, . I'II III.““ III: . . ll . I I I I I I .I . — . I . ... I . 1 , s _ . . I _ ....flU . ..I . . M -- . . . . . I T- ...: . M . _ _ , I . , I. I I J I I — t I . .0 ....u , I I v — . II ”..I .I V . — I _III. I . . .I. .. l II I t I JP: .L. I _ I. I . I l \.M w 7.. l . I I, .. VIII Ivrl. I 0 l4 IIIIII — I. ILIrJI...‘ LII-IO. IIIIIIMFII I IIHIIOI. II IIIJIIQIOIIP III-m. I IIIJII . . . I I I .IIIIIIIJIIIII II. I. 'IlIrI-JIIIlEIIIJIII III ITII II. II I..I.. ..IIIIIIII vfilIIIIQIIIHIIIIIL o "M. II — I I _ ..I. I. I. _ I — M . .. ..M: ....l. . . n . I I . I . I _ ._ .. .I .I v I ~ _ I I: . I — I I . . II. C. I r w I r I. . I I. — . .I. I ITI M . . l I I .1 I ... II *II I * II V II I l—IIII III I I II1I ..I .I I. III 0 I v I . I I'll. ”III III- I. III .MII.III I. T... I ..IIII II .. . . .5 *I w _ I. .... .I . ..I I .. v I .u . . hI.M .I a h H l M . M I . I II .. 0. 0| II 4 I O I Q fi , I1). ..I .III . "I I M I I __ I. . . I _ + . a M w I ..t I I. n I . o I o .I.. . I . . Aw . I I . M I . - t f I . I I .. I _ . . . I I ... I I I M ..I T _. . L . T+IM -I .v I TIIIIII I... II I. . I IIIII III .III I III... IIIOIIIIIIIIIIOIIOIMIIIIIIIOI II. “II. IIII'O.‘ IIIIIIIITIOII [Ir IIIIIII Il‘b‘” “ I I J IIIOI. fill-III. I1 . — I I . .I . I . . I.. . .. I , . I IL III I: .I a ._ . . . _... . . M a. .--. .M- .. - _. . . ,- . “I... . I I _ v. I . . .I I . . ..T. . . . . . . _ u . . _ 7 _.-n V . _w . . II I .. . I I — I u I. I u — I M .I II “I.III OIOIIOI .IIIII. IIIIIV III! II». I D. I l I III. ._ I .I. II 0 I.“ II I .I. . I II I. I ..I o 74 I. I I. .. d I. I I I I .. . I I I I MI. I . _ _ — 4 .kv. YH. ...IMI. , . L...IJ . I . . ,. I I . I _ . I .... I. . . . u I I4 .. M . . - . 0,. I I. . I '9 .I . M II III. or. IM ..V . ..I — . WI- 0 I.I I III I I . I Ild III}! I III. I III.-. III-I.I I III II IIIIOIII III-II. IIIIIIIIII I I II III- III-II III I TIII I III I? *1 III I»! .IL I .I I , — I fi‘. I. II . I. .. ... L... .— .. . ... — — — I ’ ~ — — II T. {I I , L I M . I I I H — _ . WA II, I I I I ,. w .I I u I Q . .. .I. M . .H I V ’01 T. Y 0. . . I I. I0 II I I I I II I* I I I III. I II II II I I I I. II I II III I ..I. I I0. .. II II I.IIILII IJWIII I -0111! III ITIIII I.I-..I IIIII IIILIIM . F u I — I II #4 o . M AIIWII ”4. III .M I ..I I LT . . . _ M . M . .. J. In . /. . M , _ - . . . .. . . .... lHM.H. -HML/ . .- -_ I III I I0. Fall. II II ..I. I.IIIIII I41 IIIIO .dF D . ‘1]...HIJIIIIIIIIJI .IIIIIIIIOIOD... IIIlrJII'DIIIJIIIl’HfIIIII .— . 4 I H I I; I I.IWI I I P III-IL. . 1 . . I .I. . ..I I O: I M II I .. I.I .. t m I . I. I .— —_ I .. I .I I I u I m n I. I — .HIIJIM II+M..I1 HUM II I. II W . I . . . I _ . i I I I . u . ...: . . 1 M r . M. ._ . . . m 1mm . . -2 -.M . I I I I I . Ida O. 0.. »_ ..V I I. .— ., I Iflc .I I I In... ..I ... If 9.. I. I I I I .VII . J4 VIII. I.IIIII I II III¢+I| III _I I. III. . . _ . . . . . .. . _ _ _ . . . I. I n . .I.” _ . Y L — _ . . . .. . . . I . ._ . . I . . . II . . . I . II I ! I . W! III I Hull r I I. III ”IIII‘IIO II. lItIIF1III1. IIIIIIIOIIIIIIII'..IIIII.IO Dill-+1 IIIIQI loll-III. IIJIIIIIWIiIIIIIII... . . .01 .11 III . . . I _.. . 0..., . ._ ... . I .. . I I I — .I.. u I u . _. . n .. m I I . . _ I . . I .Iu . I u . . . u . ... .. . z-.. ...... ....I. ... ......Ioh I. I .n I I I0 liltk II I O. I.I-I I 'L I III I , II I . I III‘ III I IIIII. IIIIIIIIIQIL . . 4 .tL “ fl. I ‘v I . I . x. .. . .. i . . I I I. . W IIII. _ _ I . m I . v. _ I I . . . $1 .~. .r .I.. . , n I {III I I . I I . I C . .I. ..u v- M . ., I.I. . .I II. I . Mrrf IL: I . . I 11 _ . ......uLIIr. . .. . . - .. II: 1+. I I. I M~ ..M. «.-. .....fi -..-.. . L . ., I I I . | .I I .nI . .. L _ . . ... ... M . -.-. . . . . _ - . - I , .I .I. I I I .IIIU Iii. III) 00.4. I II I...II ‘ M I I— .II .6 III ..I * I. t III “I. III I 1I.M .I. . — . I I I I I. . I . I .— . . I . _ . . — I I ~ I. I - . . . . _ - _ .. I I . . I . , .. . . _ __ . I ..- .. . . . . . I; .- -. I _. ‘m. . ..J . I ..I- . — V l'- .L I.,'I. I .1 I I.- I. I ... I, I _ . .. .. I.- I . II .I.... . YiIIII 9.. I II III II \ I.I.I ELI I III II. «Hm... I .r.. _. I . I.I . . I . II. , III Ell II ..I III.” . .I.}.IIIIG‘IIIIII ..._ u n .35 % Mm. TI .. . m4..- m._._ ..I.._I.. . . I. .r . . .,,. .. I..... I , . .. I .r. . I.I . .M . . I .. . .. . , . . . I , . . . -.. . n 0 Full L I I H II I-I. I o p. .. I .— ...“I I I». CHM I - I ... I . _. .. . L—. . n _. I _ . . . _ . . -.. . - -_ . “I. . U . .I ... _H _ o I _ . . IN I h P b h I I II“ II b I IIlIItIIII IIIIIIII IIIIII.‘ I In T-IM m B 001.3 00.. COLUIBI'B. OHIO. 1‘“ HOT»: ... fill-I I I II I I I I II .I II III IIIIIII II III- III I I III I I — IIIIIII IIIIII III I I — . I m u I — . I I I "III I I IIII‘IqI IIIIII I1 II I I I I IIII I III I III I u - I - . — n I , L I IIIIIII III I I l I I ..I I. I . - I I I III I I II - I I I u I I r I — I I I I I _ .1 I II I. II I I I III . I I I _ I I I l I I .I I II ,- . - _. - . _ . . . . . . . _ . . . . .- . . .. . - --. . . . I JI I I I III I II.II IIIII JIII I. II II . I I .. I . , . _ . . _ — I I I - .hH. . I _ I . I I I. I I I I II III II III—II III: .II I; I.IIL LII. I .I III. I II . . . . I . n u I I . _ I . I u. I I y u — III _‘I II III. II IIIII. I4 I. III III I I III I .II- I I III-.II . _ c u ‘ I. I - I -_ . I I . I I'll. I III II I I I III-II III I I I 7v _ _ . - u -k I J. .. - ¢ . I I u . I I 00- 11!. IIII _ I I. .I III I.I - II III- II LI I.. . . — I I I I - I u .I. . . . . . n. I- . I .. I I I I I I.#- ”I I .u I I O — . I I I u _... u I .h . — I . n _ . .. L _— . I. I 1. fl... . . _ . a . . w _..— I II .0 .II _ I I” I. I I‘... I I I .I I‘ I-.Ir I .I III II #1.. I I IIII. l l I I r I I . I. II I — I O. - . _ . . ._ . -. _.-... . . . . . - . . ..I-... - .... r-.-.... I ...I... _ .. . . .. —_ I. - -_ .I.. a I . -.. n . I . . IHIIWIIH I AIf..I.I I.I-III ..I-Al .I I - I II I I.III I _I II- III. I 9 I w I I—Il .I.-l- ! I. .I .— . .- . _ . . a . . fl . . I I M. ._ , — _ .I . I l . . . I "I I .II. _I .II-III. II II I III.- .I III" I [— I.I I II rII II III I I — I . — . I . .- h - _ .. - .. . . . _ . . ... : . .... - . .. . -- ...-I .-. ...-I. -.. .. ... . .. - .. I - . n I I- . . - . I. . .I.... {...-..- . . _, - _ - .... . a .-. an... _.., .I.. .r... - _ ... . u - . . - . . . . w. H1 .- . -_ . - .. -. - .. -13--.- _.. r - . . ,- ,_ _. . .. . . . .u. . . . . . -... u . I . I v. _ ..... I.. 4 ._I III I. II . I- I .1... I . II - _..-.I-" II 4 I- “.II- ” I ... . H ,. —I -.I . I — — I _ .. .0 I, II .II I n . I In 1i I . .. .- | ,. h I . .I.! I I _ .- . . - . z I I. I . . I I I c l r I I Y I I . . ...I I.. . .wv . . .I. .l + I . a- .I w u 1 . . I — u - - I I I-IflII‘I WIJIII II.II.IIII- I ..I- I I .- . ..- . I -.I-I r. I I .- I. .I. I. ,. - _..v- I II I I — . I —_ — n.. I I. I.I - Iv I ..I-I . - . L . d _ . I . _ . . I fI . ... - -I . . . . .. IIII . I | ..I. I I..-“ I.I}. III - II If.—.I .I.-.III II .I.-... II. IIIII II b III-III III“...- II III III. I I _ I I . ._ .I In .. I o _ . I. I. I . . J . _ . ._ - ,_ . - J ..I.. - - In I -.t .. u L— I“ . I .= .. . -I . I I I - III. IIIJ III I III III III III I I. - III I ..m I. I I - L _II . .-. I I . .I.II . . I.- ..I III — . _ .... . n _. . . u . . .. - f . ..I-”.II - - .. . L . 1:. .- . . - . .. .. . - .- I ..I. ..I... I I l . I I I A -u... I II. . I I .- I _ . .. I u I I _ w I I III ...-I I ..I I II . .— — v V.- I C L l I. II. . . u__ . . & . . I _ _ I. . I I,I . I..! I II 1 I .I III ITI. I I III- II -.I-O I l‘l II - .~I I. -. m -I r ...._ . .Ir .l .-I .I I at I . . I . I . I . _ I . ”I w ”I; I . I _ _ . .. I _ I .-n .. I I . - ..I-”II .- I I I II a II .I III I. I l I II III. I - I I.I - . . .. _ - .. . .., _ I . . ..I. I. I. ll . u . g 4 9. IO u I II .. I- . , I. . g . . .m . .I I . I I_.II II - . .. I I, - . . I , .I.- _ II I _ Ir . . . I , . I u I II I I — I I. c ,I I fl t I. OIMIWI I I I. . - .I. .II. II II I I . I III. I - II III?. III I I— I” I I _.OIHII- III-II [...-.II. n I .. I. .- . ..5 I H _ I ”I; I — I — l . . . .. . . . _ . I I II II I- III II “I I . .¢ .- I . . I - . .. .. In a _ . _.. I u . I . I01. .II .I. I ”-... .. I .I_ I _ I . .7. =0 - . I . I . .o I III. IIIIIII. III-”..I II I . III Ill—IIIIIII .II I.II..II.I II-Iw II II. III I .-M. J I I I I I II - II I n II . - . l ‘..._.II’I fl I | I _ u I I . I I . 4. II . ...- . -. - . . v. . .-- ,. - ... - .. . . ._ .. .—. . . o .n .. -. _. -. - .. -.-.-I- I.- : _ f --. _ .. . . .. . - .. - . .- . - . - . .. .-...:..... .13-.-. ... .-...- . ., . .. .- .- - - . .+ _ . . .-. - I I L I l I t . - ._ _ I I ...-I...- . I I . -I .- _ q I II II I. 9 II.- - P III I I II I III-III «II. - II. II .II. II - I .I I .I....— I o . . _T n . I I I. .h I _ r. w.- . .. - . I I.. t... --fi . -I ... .I I I . k .. _ .. .H I.- _.. uv I.. ..I-- ' . I "I _ 1n 0 . I .— I . .fl. ..¢ ~ ... II -.. . . ,. . . . - .-. - I .. _..- . I .- - . .-. .. - . ... . . .- - . rII. ”III 1$II.I II I I I - III II - I I I. III I.L.III 1 III ‘II .II II. III. 9- I I.I .. I I . -- III. . l— I. I I .I.. m I I - - _ I ; ... I . . . WI. I II [I I II..tI I II -II [III —I.I.Il I Id.III III I I _.III.II LI. .ITIIIIPII .. I c . I . . - . I . . .... . ... _ . . - v - . I I . I . II.I. II III-III I IIIII. CHI-III I. .... .. . . - - . 1:. ...U - -. -.. -. ,.... .... .-_. a 2.. .-. . I I I,. , I.. I. II I . .. .I- r I . . . . . I I ....II _—III ..II I . .- rw u I | .. _.H . w I — I a I . I O _ I —. — I — .I u . ..I.- I I PL . .II . . I. _ I I «I . 1 .I .- II I L I III -II I. . . _ v . O I . .II I ~ I . - . I II - _ 9 I . _ . I.I _ . _. .I. _ __ . . . I .II .1 III1 I I. III. I o I I I II I. I.- I _ I . I . I I r. I 2 . ..- III. . . . I.. I. .I l L. . . _ "II ..III— .II. .- I-- . u ..I- ... a . o . r I ._ . ... - . — I _ . I . _ II I . I . o 4- “If-. . I. ... a I I _q.I.I u. . Pk . _. . I . . - . .I _ I_ I - u - II I . I I , I. ‘ . a w YIIII 'I I I. I I..- ...I_ .‘I I III I .I. I. I .I I . VOL-II I. at I.- .I. - - - .II I I — I .I . I - m I — a r . . . m - _ o J .I.. I c . .. _ ..I] .I III-I I .IIII- I.I III-I. *I-II I.IIIL- III .II ... III II II II II1II III I- I_ _ _ _ . I I I - o I .I ,_ I _ - ..I . . I _.WI. I .. - V III IIqu III‘I I I II II I I III I. I I — t . . I .I - , . I . .I -. I . p A III I IIII I. . .- - . -. ... .- m -. . - . L . . - m vI II II IF- .I “all. I v _.# . I _fi- I I _ _ .J * o I u I I j I c . .- .I. .- . -- I I .I _..I II [I III IT . - 4 LI I II II. II. I - II - m . - . I . . w - . .A I .‘ II c _ .o _. I. II. a 4 I I _II '- II+.AII II I II IIII .I I II II. I a . II I II _JI I . . I p _ l o I; _r— I . .L F I ~ I I.. . — . I I II 9 I .II I 0 II . - n . I :. m . I . 1 n I r. 1 I. .II .. I I I - — . I. -. — — .1 I f - c II-..- IIO H II: II . I ~I l I I u .- I .I — I.. l I — I .I . I I .- III I . z . . . II _..III II I_IIIIII +I.I.I . v- ‘ - . . I - I. r . . w.- . . r. _ - I ._ _. ntLI I. .. - _ou- I III... . . . I fl. - I I- I . III.I.II . II IIIJII.LIIII+I.. III- II I I . ...I ‘I I 0L . .o _ .- _eI _ I1! . I - .. - . - . — . .14- r I . _ —0 — F.l. . . A - - I . .. _ : . _.- -. - . .. _ . . . . - . . - u . I- ...! .- ..I-I- ...rlr .. | .- . a . — . - -... _. . I.. .-r r w- 09. .I.-II. II- I .l I . . . . _ _ I L I I II. o~ _o I o I ”I “o l- _ II- I .I I IIIII I I I I I . II .II. I I .- II .- I .I I 9' w ..I . .I - ..I I .I I III - I. L . I - .I ..- I. .I.... I -.0- TI — III III — - I“ . . — -.- r .— I _ . , - u . . .II -. I .II n I . .. .H I. . . .I . .. . I I . I I _ ..I . I I IIIIO II I‘II I I I I III III. If...- II. II [III-k - . I _ . . .I . - — _ c I o I . I I .I _ . . III I. I . -. . I r I .MS. . H . . .. -. J. r .I . ..I .- THIN-II I .. I. I..-II . . II .IL I I. _III I u . IHL+ .... IW..I..I_.I u I m - . I - . - I ... I . . . 1. . _. , - . _. . - III 1 . Tl _. ...I 1 . .. _ I _-...u- .. . .. .. . . - T . . T .- . .... I I I . $I _. . .l V. .II ..I ..I .I w I ‘I. - ‘I I — . b I . I ..l . . .....a- .I. . . . .. ...... . . - .. _ . r - - I I. I- - . I I ._ - H ,Y m -- . I .. fi .. I _ wt o¢ II . II III .I- IL-I-Iltvu- 9|.I .. - II.- I _ .- . . J - - . -. u _ . I . .. p..- r .S H .- . I. . .. . .. . _ q” _ . .. . - .I.! VIII. _ III _I III-..I I ..II III .IIOwIII _I I J IIII. (I m — .I I . I .I a I % I. o I - I.-- I II IIII I. I II I. I . . - If. — I _ :- ca. I m I. I - I II. I" —OI-II IIIIII IHIIIIIII ILIIIIII IIIIIIIII . I III .- .. I I . l . . . . . — . . . - - . _ . I. _ . . u - . I .. _ . m _I ..I III I IIIIII I I I..-II. I III-I I I. I .I. _ . . - I . , . . .... ...h I . ...-I--.- .---.U .I.-...... . .. . .n . - 1 .V ..- . _ - I I . “I. In _ I , . I VIII Iva II* III ITIIIIF-JIII IIIOI I I» . III PI I o I . I. . . r --I _ . II . . I L ..I. . — ., II — . I _ I I I -~ . 5 L7 . I.I. - . .II F. III .II. . I . ... . - . I ...b PI. . I ; . . .. _ . I . -- o h .. J . .-III I .I.I...-I IIJIlIII.II_iIIII.II....I. IIsIIIIII. . . . . ... . . . F- . I. — . m _ I. III — - . . II . . .. . .- . I I.I I II I II III 'IIIII III-.II III. II IIII .II. I III. I I . v I . . *u_ II... I. I I .- . v - .1 I w H- L I. . . . - . I ” I. c .. . . . I .I .. — - .II II —III I III I .II IIII “ II I II - I l I I I. i I 0 I I IIII II I . . ._ _ n _ . - . p . - . ., I ' I I I.I-I I _ _ I . .- w I I I _ r5: II .\ I. . .. ...-I I _ _ ... - o I . —. I I I i . IIFIIIHII I II." .II-ITII-v .I”I.IIII- III . .. .. - I a . . - . _ - . a . r . - ..I- .. . . _ _ . . I _.. - _ . u u .m . u . I—. I I 0 III I.I II . III II ... I . v .. . . I . I I 4 - n V I I I I..- III I IunI I I I I.II II . c I . —II H, w. 1 w . .- fi 4 . I I I... I I OI III .II I I I F.III IIH II I M .II I II I I.IIII I I. III A . . o I ow I — . p I . . I ..I. _ . . __ .. . .- - . . . . . - I . . . . - .. .-.... I. . HIV I f .. .. .. .. . . ... . ~ . I — - .I. .. I I . . .4 I 4 . I. n I. . . . _ I. .- _ II I I ~.. I a II I . .. I .I - .. . . I . h H - .. — If - . . n . b 4 .. - a I I II I... I F . _. — u I. I I II III I 0‘“ . . ... L. _ ..- . I o _' - n . . . II‘IIIII I -. I I I ...v r.- v - - - w J . I . . .. . .- .I. 1. II. a OI . I I o IIIOI 0 II .I.! L I J -. III . I- In . I I.I I.I“. :I. I. “-.I-r T I . I , n . . . I I! , I I - I I . I.. . . —. _ . . . I I . -. ... I o . , ~.. _ .- ... . .I _ I - I - I I I o. I I I. . . __ . v vl .II. ..III HI I .... .II I L I *. i ..I“ . II ~I .. . .. .. .I. - I ‘ I. I ‘ I I. . I I ..— — . . - .. . E 1 YE. . I - I I .- . I+I.— . . “I... I IL... I Ll” I-..rIp I. I+ I r - . I.. . u I._ I — _ _ I I .. I r- . . III. I -I , o . L. . Iii . .- .1 $.I... _Ifd I I . I I I. IIII I‘I-I I.I I DI _ . 4 I . A . , .. - ..I. . . I . - . . I . ..I I I L. . v. - . .. _. . . .. .. .u .. -. .. #3. .M ...II . . ... I. ....flr ..- +.- _...II...-...--.. --.-.I.--- - I I . . _ _ I I -. I I . . — I _ .U II I . . . . . . .. I . II In I I m I I n. I n I I I I o I I . I" O I ’ I I I . I. I . . ~ . +.- :L n I . . I I u . I I I l L I I_ . I - I. _ I I I 95.3 I - . I I . — I. I l- .I - I . .— . .. I . I u _ . . o I ..I I - .I....- _ Q I.. II I I I“ I r... 1 n I 71. .. . . . _ n . . _ . . . I - . —. _ «I . - I ._ 4 u I I L IrlI IIIIII I 'L. I. . II ..I .I— n I . I u I . I . I .m - . . _ .u- r . 1 I .-.u _ . . — II II I II IIIIII I I I I I IIIIII L IIII IIF I C II I- — I - I , ..Il . .. I-. .. .... h PL L I! ‘I'HI H (JUL! 00.. COLE-"813. OHIO. 3'6. ‘I £2904". Interpretation of the resistivity readings may be ex- plained by taking a representative curve. The curve for sta- tion B-l, plot #2 will be used for that purpose. The decided rise from depth three to six feet is caused by a layer of high resistivity. The fact that this rise is shown in only one reading indicates a layer of only one and one half to three feet. The curve then drops rapidly as the effect of the underlying clay enters. At fifteen feet the penetration reaches sand which causes a positive increase in slope. The flat slope, rather than a rise, from there on is due to the fact that the penetration has reached the water table and accumulated soil acids have somewhat reduced the re- sistivity of the sand. 37 . iltxl‘llné..flu I551... of?» : v...) M.‘. ~00NCLUSIONS- Upon completion of this experiment the following con- clusions, based on the results of the survey, were derived. The method as outlined may be used for shallow depths with a moderate degree of accuracy. For depths less than twenty or twenty five feet in clay, sand or other material free from gravel, more definite information can be secured with a soil anger in approximately the same length of time. For depths greater than twenty five feet, the electrical method has a distinct advantage over the use of a soil anger in that the boring is occasionally hampered by rocks and the anger is awkward to handle. A reduction in.moisture content within the limits ob- served has the effect of lowering the resistivity curve with- .out appreciably changing the slope. This does not interfere with the interpretation of results thus obviating the ne- cessity of moisture determinations for a survey. In surveys in areas of glacial drift, such as was en- countered in this survey, there is considerable lateral var- iation in soil materials which must be considered in the in- terpretation of resistivity readings. Care must be exercised in the handling and use of the equipment. Electrodes should be inserted in the ground the same distance for every reading and good contacts must be assured. The immediate area should be free from loose pieces of bare wire and any other metal condutors. It was found that the use of a metal tape, in contact with the ground, 58 affected the readings to an appreciable amount. For future research in this field, it is suggested that the Line Electrode method, which has been briefly described in this paper, be thoroughly investigated. Further determin- ation of moisture changes should be obtained over a much longer period of time and for a greater variation in con- ditions. The variation of weather conditions and length of time in this survey was not sufficient to arrive at any pos- itive or complete conclusions. Readings should be taken with various increments to determine the change in resistivity curves, if any. 39 " ... MHT... .31.... 2“ BIBLIOGRAPHY Eve and Keys - Applied Geophysics Eng. and Contracting - Vol. 68, No. 5 Public Roads - Vol. 16, No. 4 Comp. Air Mag. - Vol. 39, No. 5 Jakosky and Wilson - A.I.M.E. Tech. Pub. 515 Transactions - A.I.M.E. - Vol. 110 40 ROOM use ow ‘(Wa 23>, MICHI‘GAF. S’ATE UN.VERS'Y V LIBRARIES ”3" l' “a, "In w ;;* it! w I a Ml ,llwl;lt.,lly: F.‘ JM‘ 93 0307 12 10960