Transactions Template JOURNAL OF ENGINEERING RESEARCH AND TECHNOLOGY, VOLUME 2, ISSUE 2, JUN3E 2015 141 Dependency of dry density of soil on water content in the measurement of electrical resistivity of soil Chik, Z. 1 , Murad, O.F. 2 , Rahmad, M. 3 1 Professor, Faculty of Engineering and Built Environment,Universiti Kebangsaan Malaysia (UKM), irzamri@gmail.com 2 Student, Faculty of Engineering and Built Environment,Universiti Kebangsaan Malaysia (UKM), murad5353@yahoo.com 3 Student, Faculty of Engineering and Built Environment,Universiti Kebangsaan Malaysia (UKM), muhamadrah- mad29@gmail.com Abstract— Density is defined as the weight of soil per unit volume of soil. Often in the construction of different types of structures in-situ 'fill' is required. In-situ measurement of density is vital for such projects. When soil is being used as fill material it is usually compacted to a dense state to obtain satisfactory engineering properties. Dry density of soil basically depends on many properties of soil. For this reason it is difficult to establish an empirical relationship between electrical resistivity and dry density of soil. For similar typ of grain size distribution and dry density of soil, electrical resistivity widely varies with different percentages of water content. In this study dry density of soil was determined using standard proctor test. After compaction electrical resistivity of soil was measured for different dry density of soil. From the graph of volumetric dry density of soil versus water content of soil, a slightly steeper increment in dry density can be observed with increasing water content. On the other hand in the case of dry density versus electrical resistivity graph, electrical resistivity remains almost same for increasing dry density until it reaches to the peak value. After achieving the maximum dry density a detrimental slopes can be observed in the both graphs. In the case of electrical resistivity of soil, after achieving maximum density of soil it does not decrease in remarkable extent. So except some dissimilarity a common trend can be observed in the both of the graphs. In both graphs after a maximum value, dry density tends to reduce. Also in both cases measured maximum dry density of soil was 1.79, 1.936, 1.792 and 1.821 gm/cm3 respectively. So it can be concluded that for both cases electrical resistivity mostly depends on percentages of water in the soil rather than dry density. It is difficult measure dry density of soil from only electrical resistivity. But the maximum dry density of soil can be found from the least resistivity value. Index Terms— density, electrical resistivity, percentages of water, maximum soil density I INTRODUCTION Density is the mass of solid particles divided by the volume of solid particles. The mass of soil excludes pore space and organic material. A high bulk density is indicative of either soil compaction or high sand content. Most soils have a densi- ty between 1 and 2 g/cm 3 . Dry density of soil represents well- defined properties of the materials. It is an indicator of soil compaction and soil health [1]. It also provides valueable inforformations such as porosity and void ratio of soil. In terms of agriculture dry density of soil indicates structure of the soil and soil suitibility for growth of plants. Different physical, chemical and biological properties of soil such as infiltration, available water capacity, soil porosity, plant nutri- ent availability, and soil microorganism activity affected by dry density of soil. So many geophysical methods were used to measure the degree of compaction both at the site and in the laboratory. Among all geophysical methods electrical re- sistivity is a non destructive and comparatively less time con- suming method. Other conventional methods for determina- tion of soil compaction are invasive as well as costly [2]. As it is basically the ratio between mass and volume of the soil, theoretically the value of dry density mostly depends on the mass and the volume of the soil. So the properties that affect both mass and volume such as grain size distribution, soil compaction etc indirectly affect soil dry density. However water content is one properties of soil that directly affect dry density. For every type, grain size of particles there is a spe- cific moisture content in which the density of soil is maxi- mum. But properties of soil such as grain size distribution and soil compaction have comparatively less effect than moisture content in the electrical resistivity of soil. This is a major problem for determining soil dry density using soil resistivty. II PREVIOUS WORKS ON DRY DENSITY MEASUREMENT USING DIFFERENT GEO-PHYSICAL METHOD Among many geo-physical methods that have been used for the measurement of soil density, Multichannel analysis of surface waves (MASW), soil conductivity and soil resistivity are most popular methods . Kalinski and Vemuri studied soil compaction using Electrical Conductivity Measurements in 2005. The researchers proposed a new method CQA based on mailto:murad5353@yahoo.com Chik, Z., Murad, O.F., Rahmad, M/. Dependency of dry density of soil on water content in the measurement of electrical resistivity of soil (2015) 142 θ [3]. In the year of 2011, Laloy and Javaux used electrical resistivity in moisture content or bulk density of soil meas- urement incorporate with ―pedo-electrical‖ function. In that study five pedo-electrical models were used to reproduce electrical resistivity as measured by ERT in silt loam soil sample within specific range of moisture and bulk density. In this purpose the Waxman and Smits model, the Revil model, the volume-averaging (VA) model, the Rhoades model, and the Mojid model were inverted within a Bayesian framework to identify the optimal parameter, parameter uncertainty and its effect on model prediction. Sensitivity of the electrical resistivity was studied using calibrated VA model and found that approximately 1.5 times higher sensitivity to soil mois- ture content than to soil bulk density. In addition, the sensitiv- ity of electrical resistivity to soil moisture and soil bulk densi- ty was found to increase as soil moisture and bulk density decreased [4]. On the same year of 2011, Chik and Islam studied on soil compaction estimation using electrical resistivity including chemical characterizations in the soil. In that study four dif- ferent types of soil was considered. Standard Proctor compac- tion tests, was carried out for all types of soil sample. Electri- cal resistivity was measured for compacted soil sample with different percentages of water contents (Figure 1). Recently Lin and Sun evaluated model-based relationship between cone index, soil water content and bulk density using dual-sensor penetrometer [6]. III METHODOLOGY Soil sample was collected from a slope side near New FKAB building UKM, Malaysia. Four samples were collected from four boreholes at different slopes. Then soil grain size distri- bution was determined using sieve analysis . Sieve analysis was important because soil resistivity defers with the type of soil. According to Unified Soil Classification System (USCS), this average type of soil taken from four boreholes is basically clayey sand (SC). The portion of sand in this type of soil is more so the resistivity value was less. Because clay fillup the voids between which eases the transfer electricity between soil particles. Soil sample was mixed with different percentages of water within the range of 5 % to 25% (Figure 2). For measuring the exact percentages of water mixed with soil sample following equation (Equation 1) was used, 𝑢 = 𝑚 − 𝑚 𝑚 𝑋100 % (1) Where, 𝑢 = Percentage of moisture content 𝑚 = Wt. of soil + water 𝑚 = Wt.of dry soil Then the sample is compacted using standard proctor. After that the dry density of soil was measured. As the percentages of TABLE 1 Grain size analysis Sieve No Sieve opening (mm) Wt. of soil retained (gm) Percent soil retained Cumulative percent retained Percent finer 4 4.750 117.15 6.5 6.5 93.5 8 2.360 595.19 33.2 39.7 60.3 16 1.180 383.62 21.4 61.1 38.9 30 0.600 235.77 13.2 74.3 25.7 40 0.420 181.87 10.1 84.4 15.6 50 0.300 208.58 11.6 96.0 4.0 100 0.150 66.48 3.7 99.7 0.3 200 0.075 3.31 0.2 99.9 0.1 Pan 12.20 0.7 Figure 1 Dry density and soil resistivity for different of water contents in various soil sample [5]. Figure 2: Location of soil sample collection Chik, Z., Murad, O.F., Rahmad, M/. Dependency of d ry density of soil on water content in the measurement of electrical resistivity of soil (2015) 143 water increased dry density of soil also increases gradually. But just after the maximum dry density of 1.79, 1.936, 1.792 and 1.821 gm/cm 3 respectively, it started to decrease with higher percentages of water content. For measuring the dry density of soil follwing equation (Equation 2) was used, = (2) Where, = Bulk Density of soil =Mass of the soil particle = Volume of the soil particle Just after compaction the resistance of soil was measured using two probe electrical resistivity meter (KYORITSU) (Figure 4). 4 cm distance was considered between the probes. Finally the resistivity of soil was measured using following equation (Equation 3), = 2𝜋𝑎𝐴 (3) Where, = Resistivity of soil 𝑎 = Distance between the probes 𝐴 = Ristance of the soil between the probes IV RESULTS AND DISCUSSION Electrical resistivity of is the opposite electrical properties of conductivity. As water is a covalent liquid, the ions are held together by sharing electrons. Most covalently bonded liq- uids are not electrically conductive because the electrons, which essentially act as the medium by which the electricity travels, are tied up between the atoms they are related to. Also small amount of water does ionize and increase the elec- trical conductivity of soil. Due to the effect of water content electrical resistivity of soil tends to decrease with the increasing amount of water con- tent. For borehole 1, from 7.7 % to 11.78 % of water content electrical resistivity between the soil sample drop-off about 104 (KΩ-m). But after a certain level, resistivity does not Figure 3: Graph between Dry Densities vs. Water Content Figure 4: Measurement of electrical resistance after compaction of soil TABLE 2 Dry density and Electrical resistivity of soil for differ- ent percentages of water content Borehole Percentages of water (%) Dry Density (gm/cm 3 ) Electrical Resistivity (KΩ-m) BH 1 7.7 1.62 108.071 9.94 1.662 20.86022 11.78 1.68 5.02656 14.18 1.724 3.76992 15.96 1.79 2.51328 19.42 1.676 2.261952 23.68 1.564 2.261952 BH 2 7.723 1.685 123.2451 9.95 1.812 40.36958 12.36 1.868 13.365916 14.88 1.936 3.3211 16.12 1.8345 3.293211 18.98 1.652 3.2995 23.87 1.523 3.2855 BH 3 6.6 1.523 196.211 9.65 1.632 22.3311 11.65 1.698 11.321 14.962 1.792 4.31544 16.33 1.6932 4.325 19.97 1.6236 4.3111 24.102 1.523 4.3211 BH4 8.44 1.526 160.2113 10.95 1.695 63.2525 12.3669 1.725 9.255 14.978 1.821 5.361 16.321 1.654 5.321 18.966 1.5622 5.35111 24.654 1.459 5.3569 Chik, Z., Murad, O.F., Rahmad, M/. Dependency of dry density of soil on water content in the measurement of electrical resistivity of soil (2015) 144 decrease with the increasing amount of water content. Be- cause at that certain percentage of water content, soil density is maximum so the electrical conductivity is also maximum at that specific water content (Figure 5). Simillar trends can also be observed for other boreholes. From the graph between dry density and electrical resistivity it can be observed that electrical resistivi-ty gradually de- creases with the increase of soil dry density (Figure 6). But just point density increases dramatically with the slight reduc- tion of electrical resistivity soil. However electrical resistivity almost stops changing at approximately 2.51 KΩ-m. After that dry density of soil, electrical resistivity remains constant with the lower dry density of soil sample. From Fig 2 and 6 it can be observed that, in both graphs for the dry densities of 1.79, 1.936, 1.792 and 1.821 gm/cm3, trend line of changes its direction. But water content decreases grad- ually with decreasing dry density of soil. On the other hand after maximum density of soil sample, electrical resistivity does not change with the dry density. So it can be understand that for optimum mois-ture content of soil sample, electrical resistivity is minimum. Within this spe- cific percentage of water, electrical conductivity of soil is max- imum. Even if more water is added with the soil, it does not have any effect in electrical conductivity. Also at maximum dry density, soil grains supposed to be placed closest position with each other. For this reason maximum dry density provides min- imum resistivity of soil sample. V CONCLUSION Compaction of soil is one of the vital parameter for geotech- nical engineering. Dry density of soil is directly related with the compaction soil. It is more expensive and time consuming to collect the soil sample from the site and measure the dry density of soil in laboratory. For this reason it is much con- venient to measure the dry density at the site of construction using electrical resistivity of soil. But it is very difficult to measure the exact soil density because of water content of soil. In this purpose resistivity ratio between different layers of soil can be considered to avoid the effect of water content on resistivity of soil. Though resistivity mostly depends on the water content of soil, at least maximum dry density of soil can be deter-mined using soil electrical resistivity. ACKNOWLEDGMENT The authors wish to thank all the laboratory assis-tants of Geotechnical Engineering laboratory (UKM). This work was supported in part by a grant from ERGS/1/2012/TK03/UKM/01/3 and GUP- 2012-031. REFERENCES [1] I. D. Lestariningsih and K. Hairiah, ―Assessing Soil Compaction with Two Different Methods of Soil Bulk Density Measurement in Oil Palm Plantation Soil,‖ Procedia Environ. Sci., vol. 17, pp. 172–178, Jan. 2013. [2] F. I. Siddiqui and S. B. A. B. S. Osman, ―Electrical Resistivity Based Non-Destructive Testing Method for Determination of Soil’s Strength Properties,‖ in Advanced Materials Research, 2012, vol. 488–489, pp. 1553–1557. [3] M. E. S. C. V. Kalinski, ―A Geophysical Approach to Construction Quality Assurance Testing of Compacted Soil Using Electrical Conductivity Measurements (ASCE),‖ in Earthquake Engineering and Soil Dynamics, 2005, pp. 1–10. [4] E. Laloy, M. Javaux, M. Vanclooster, C. Roisin, and C. L. Bielders, ―Electrical Resistivity in a Loamy Soil: Identification of the Appropriate Pedo-Electrical Model,‖ Vadose Zo. J., vol. 10, no. 3, p. 1023, Aug. 2011. [5] Z. Chik and T. Islam, ―Study of Chemical Effects on Soil Compaction Characterizations Through Electrical Figure 6: Graph between Dry Density and Electrical Resistivity Figure 6: Graph between Dry Density and Electrical Resistivity Figure 5: Graph between Electrical Resistivity and Water Content Chik, Z., Murad, O.F., Rahmad, M/. Dependency of d ry density of soil on water content in the measurement of electrical resistivity of soil (2015) 145 Conductivity,‖ Int. J. Electrochem. Sci., vol. 6, pp. 6733–6740, 2011. [6] J. Lin, Y. Sun, and P. Schulze Lammers, ―Evaluating model- based relationship of cone index, soil water content and bulk density using dual-sensor penetrometer data,‖ Soil Tillage Res., vol. 138, pp. 9–16, May 2014. Prof. Zamri Bin Chik. Dip Civil Engg (UTM), BSc (Aberdeen), MSCE,PhD Pittsburgh), P.Eng, MIEM, CPESC (Geotechnical Engi- neering) Mohammad Omar Faruk Murad. Completed B.Sc. in Civil Engi- neering from Ahsanullah University of Science and Technology with Dean’s list of honor.Continuing Masters by Research in Geotecnical Engineering in Universiti Kebangsaan Malaysia (UKM). Presently working as a Graduate Research Assistant (GRA) at Universiti Ke- bangsaan Malaysia (UKM). Muhamad Rahmad. B.Sc. in Civil Engineering in Universiti Ke- bangsaan Malaysia (UKM).