Paper 4 Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 1 Effect of Clay Percentage in Sandy Clay Soil on Saturated Hydraulic Conductivity Dr. Khitam Abdulhussein Saeed Iraq-Baghdad Al-Mustansiriya University-College of Engineering Email: khitamhussein@yahoo.com Received 28 June 2015 Accepted 9 December 2015 ABSTRACT: Hydraulic properties of sandy clay soil are very important for filtration, seepage and irrigation; so set of experiments were carried out for different samples of sandy clay in Baghdad. Measurements include bulk density, particle size distribution, clay percentage and hydraulic conductivity using constant head system. The aims of this study were to estimate equivalent saturated hydraulic conductivity (Ks) for different clay percentages and predict porosity of sandy clay as function of clay percentage and porosity of sand and clay. Nine samples of sandy clay soil have been tested in a hydraulic and soil laboratory (Mustansiriya University). Semi-empirical model was correlated to evaluate saturated hydraulic conductivity from clay percentage and results were compared with five empirical models selected from published literature were also used to predict Ks. These empirical models were (Puckett ,1985) , (Ryjov and Sudoplatov,1990), ( Dane ,1992), (Dheyaa ,2001)and (Shevnin.et al, 2006). Keywords: soil, sandy clay, hydraulic conductivity, porosity اثر نسبة الطين في الترب الرملية الطينية على التوصيل الهيدروليكي المشبع د. ختام عبد الحسين : الملخص ةيمول دورا لرترحودلجالار وا لالورل لوجلي ادر وع ةامااول ةوب التاووول ل موو الخواا اليدروللديدول لرتورل الرةردول الةد دولتعتبر .حوومرع الادوتوووك الي و وول ال,ولر وولجالتام الباموو لرببدبوكج وووبل الةوودب لالما ووردل ةخترفوول ةووب التوورل الرةردوول الةد دوول وو وورا ل المشبعل الميو ئل ل وب ةخترفل ةب . اا اليرف ةب الرواتل لا لتاددم الما ردل اليدروللديداليدروللديدل ةوتعمردب ,وم االوتفوع ال و ع توو موو ةوب توم بو كرالول ل ووبل الةودب لالموووةدل ليوا ةوب الةودب لالرةوا.الةدب لكجلي الت بو ولمووةدل لرترل الةد دول الرةردول حوب تار بو لتادودم أاتمر و ةعولاول ال تووئل اروو موا الترل الرةردل الةد دل ةختبرل الماائ لالتر ل الاوةعل الموت صور ل. ا الك تةبدادل ةختووة ةب ة شاواك تو ال الت ا ضو قدموع الما ردل اليدروللديدل المشبعل ةب وبل الةدب لتمع ةاوو ت ة خمس ة ةب الما ردل اليدروللديدل المشبعل للجه الما الك ليا (Puckett, et al,1985: Ryjov and Sudoplatov,1990: Dane,1992: Dheyaa ,2001 : Shevnin,2006) mailto:khitamhussein@yahoo.com Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 2 1. INTRODUCTION Hydraulic conductivity (K) is the constant of proportionality in Darcy’s Law and as such is defined as defines the rate of movement of water through a porous medium such as a soil or aquifer or the flow volume per unit cross-sectional area of porous medium under the influence of a unit hydraulic gradient (m/d) commonly used units for hydraulic conductivity shown in (Table 1) (Puckett et al, 1985) and (Nakhaei, 2005). Soil water potential is the driving force behind water movement. The main advantage of the "potential" concept is that it provides a unified measure by which the water state can be evaluated at any time and everywhere within the soil-plant-atmosphere continuum (Hillel, 1980). The forces subject soil water include gravity, hydraulic pressure, the attraction of the soil matrix for water, the presence of solutes, and the action of external gas pressure .At any point in the soil, total soil water potential is the sum of all of the contributing forces(Hillel, 1980). Measurement of hydraulic conductivity is problematic, considering the parameter can differ over several orders of magnitude across the spectrum of sediments and rock types, as indicated in (Table 2). The parameter can also vary markedly in space, even with apparently minor changes in sediment characteristics. Hydraulic conductivity is influenced by the properties of the fluid being transmitted (such as viscosity) as well as the porous medium (Ranieri et al, 2012). Hydraulic conductivity is also scale dependent, so that measurements taken at the core sample level may not be directly extrapolated to the aquifer scale. It is also direction dependent, so that hydraulic conductivity can be markedly different in the vertical from the horizontal. Hydraulic conductivity cannot be directly measured but inferred from field, laboratory or modeled data. 2. THEORETICAL APPROACH In Darcy’s law, saturated hydraulic conductivity is a constant (or proportionality constant) that defines the linear relationship between the two variables J and i (figure 1). It is the slope of the line (J/i) showing the relationship between flux and hydraulic gradient. Solving Darcy’s equation for K yields J/i (see equation 1). K = J/i (1) Flux (J) is commonly expressed on a volume basis, and the units simplify to m/s. The hydraulic head difference (ΔH) is commonly expressed on a weight basis. It simplifies to centimeters of head, and the hydraulic gradient (i) becomes unit less (e.g., cm/cm) (Ranieri et al, 2010). Then, Ks takes the same units as flux (m/s). Flux represents the quantity of water moving in the direction of, and at a rate proportional to, the hydraulic gradient. If the same hydraulic gradient is applied to two soils, the soil from which the greater quantity of water is discharged (i.e., highest flux) is the more conductive (greatest flow rate). The sandy soil yields a higher flux (is more conductive) than the clayey soil at the same hydraulic gradient as shown in Figure (1). The soil with the steeper slope (the sandy soil in figure 1) has the higher hydraulic conductivity. Hydraulic conductivity (or slope "K") defines the proportional relationship between flux and hydraulic gradient, or in this case, of unidirectional flow in saturated soil. Saturated hydraulic conductivity ("Ks") is a quantitative expression of the soil’s ability to transmit water under a given hydraulic gradient (Mason et al, 1957). http://soils.usda.gov/technical/technotes/note6.html#ref#ref http://soils.usda.gov/technical/technotes/note6.html#ref#ref http://www.connectedwater.gov.au/framework/hydrometric_k.php#table2 http://soils.usda.gov/technical/technotes/note6.html#eq5#eq5 Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 3 The hydraulic conductivity for a given soil becomes lower when the fluid is more viscous than water. Hydraulic conductivity (or Ks) is expressed using various units. The units and dimensions depend on those that are used to measure the hydraulic gradient (mass, volume, or weight) and flux (mass or volume). To provide national consistency in defining permeability classes in soil surveys, Uhland and O'Neal (1951) evaluated percolation rates of about 900 soils. They defined "permeability" classes by distributing the percolation data equally among seven tentative classes (Table 2). Along with percolation data, they also studied 14 soil morphologic characteristics that affect water movement and that could be used to make predictions regarding permeability class. Because of management effects on surface horizons, they confined their study to horizons below the surface layer. These classes were published in the 1951 Soil Survey Manual (Soil Survey Staff, 1951). Mason et al. (1957) statistically analyzed Uhland and O'Neal's data. They concluded that it was overly optimistic that one could correctly place a given soil into one of seven permeability classes on the basis of percolation rates of five core samples taken at one site (the probability of being correct was 30%). A reasonable degree of reliability could be achieved if either more sites per soil were sampled or fewer classes were used. The study suggested that a 95% probability of making a correct placement could occur by using three to five permeability classes. In 1963, the NCSS National Soil Moisture Committee proposed a class/subclass "choice schema" with five to seven classes (Table 2) (Soil Survey Division, 1997). The proposal was provisionally accepted, pending the outcome of discussions comparing auger-hole percolation tests with the Uhland core method and pending additional information on critical limits. When the Soil Survey Division converted its previous database to the National Soil Information System (NASIS) in 1994, saturated hydraulic conductivity replaced permeability. Only the name was changed at this time. The values from the previous database were imported directly into NASIS without modification. Krumbein and Monk (1943) proposed the equation: K=b(dm) 2 exp ( -σΦ ) (2) Where k is in darcies (1 darcy = 9.87E -09 cm 2 ), dm is the geometric mean grain-size diameter (mm), σΦ is the geometric standard deviation (in Φ units, where Φ is –ln(d) and d is the grain-size diameter in mm), and a and b are empirical constants. This equation was based on experiments performed with sieved glacial outwash sands that were recombined to obtain various grain-size distributions. Kozeny (1953) proposed an equation based on porosity and specific surface that may be written as (Marshall 1958): K=n 3 /(S 2 p (3) Where k is in cm 2 , S is the soil surface area of the medium per volume (cm 2 /cm 3 ), and p is an empirical constant. Marshall (1958) went on to derive an equation for an isotropic material in which the mean radius of pores for each of ‘m’ equal fractions of the total pore space are represented by the corresponding mean radii (r1, r2, . . ., rm): http://soils.usda.gov/technical/technotes/note6.html#ref#ref http://soils.usda.gov/technical/technotes/note6.html#table2#table2 http://soils.usda.gov/technical/technotes/note6.html#ref#ref http://soils.usda.gov/technical/technotes/note6.html#ref#ref http://soils.usda.gov/technical/technotes/note6.html#table2#table2 http://soils.usda.gov/technical/technotes/note6.html#ref#ref http://soils.usda.gov/technical/technotes/note6.html#ref#ref Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 4 K=1/8{n 2 m -2 [r1 2 +3r2 2 +5r3 2 +……(2n-1)rn 2 ]} (4) Where k is in cm 2 , ri (cm) is the mean radius of the ith fraction, and r decreases in size from r1 to rm. Shepherd (1989) extended Hazen’s work by performing power regression analysis on 19 sets of published data for unconsolidated sediments. Ks=cD 2 10 (5) The data sets ranged in size from 8 to 66 data pairs. He found that the exponent in Equation 8 varies from 1.11 to 2.05 with an average value of 1.72, and that the value of the constant c is most often between 0.05 and 1.18 but can reach a value of 9.85. Values for both c and the exponent are typically higher for well-sorted samples with uniformly sized particles and highly spherical grains. 3. EXPERIMENTAL WORK There are relatively simple and inexpensive laboratory tests that may be run to determine the hydraulic conductivity of a soil: constant-head method and falling-head method. The constant-head method is typically used on granular soil as shown in figure (2). This procedure allows water to move through the soil under a steady state head condition while the quantity (volume) of water flowing through the soil specimen is measured over a period of time. By knowing the quantity Q of water measured, length L of specimen, cross-sectional area A of the specimen, time t required for the quantity of water Q to be discharged, and head h, the hydraulic conductivity can be calculated: K=V L /[A t (H2-H1)] (6) The total head loss through the permeameter is indicated by the difference in elevation between the inflow and outflow water levels. 3.1 Laboratory Methods Constant-head methods are primarily used in samples of soil materials with an estimated K above 1.0 × 10 2 m/yr, which corresponds to water filters medias. Important considerations regarding the laboratory methods for measuring K are related to the soil sampling procedure and preparation of the test specimen and circulating liquid. The sampling process, if not properly conducted, usually disturbs the matrix structure of the soil and results in a misrepresentation of the actual field conditions. 3.2 Materials and Methods Samples were classified according to particle size using a standard British Soil Classification System, detailed in BS 5930: Site Investigation. The samples were classified, diameters of soil particles at 10%, 20% and 50% cumulative weight determined, and the coefficients of uniformity, intercepts and porosity values were calculated. Since the kinematic coefficient of viscosity is also necessary for the estimation of hydraulic conductivity, a value of 0.0874m 2 /day (0.897 *10 -6 m 2 /s) derived for a water temperature of (24-26 o C) is measured in the laboratory. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 5 4. RESULTS 4.1 Prediction of Porosity of Sandy Clay Soil The total porosity nsc of the sandy clay soil is calculated from two empirical forms, the first is (Ryjov and Sudoplatov,1990) equation as following expressions: nsc= (ns - C ) +nc.C, when C