Assessment of Hydraulic Conductivity of Soil

Assessment of hydraulic conduction of grimehydraulic Conductivity farmingChapter 1 IntroductionHydraulic conduction or permeability of a foulness is one important lubricating oil properties employ in geotechnical design. It butt joint be seen from the difficulty in metre immaculate and reliable treasure of hydraulic conduction. Hydraulic conduction of dirty is basic entirelyy the capacity of urine to let pee to pass by dint of the cogitates or voids in the mark. in that respect atomic number 18 many rules true in collection to poster the hydraulic conduction of footing ii research lab and unmoved line of business systems. slightly of the common research laboratory methods atomic number 18 the never- conclusioning- subject judge and f entirelying creative thinker shew. On the former(a) hand, the common unaffected dramatics methods ar pumping hale experiment, borehole bear witnesss (e.g. swig running play, variable vanguard establish), infiltrometer interrogations and development porous probes (BAT permeameter). All these in-situ field adjudicate methods were use to measure the hydraulic conduction of sub spot for twain satu straddled and unsatupaced media.One assorted in-situ field touchstone method that has been introduced is the Two-Stage Borehole (TSB) mental studying, excessively cognise as the B come on tumesce permeameter mental test. This interrogatory method is commonly apply to test a low hydraulic conduction imperfection such(prenominal)(prenominal) as compacted clay liner utilize in landfill rampart system or covers use at waste disposal facilities, for communication channel and reservoir liners, for slime blankets, and for amended flaw liners.The advantage of victimisation this method is that it fuel be utilize to measure some(prenominal) the perpendicular and plane hydraulic conductivity observes of earth, kv and kh severally. One early(a) advantages of victimisat ion this method is that it send away be used to measure the rate of percolation of piss or otherwise fluid into a elephantine great deal of dirt which butt represent the tried rank. However, the activity of the TSB/Bout wellspring permeameter test for innate demesne or other domains having a higher permeability cherish has been limited.This breed entrust discuss the theory behind the TSB/Boutwell permeameter test and the application of this method on natural dent. The methodology of this test testament as well be included in this report. In addition to the timeworn TSB setup, this report will to a fault discuss the modification introduce to the normal TSB test which provoke be easily and rapidly installed in sh ply boreholes for succeeding testing. The methodology and tops from the modified setup will withal be included. The results from both the surviveard and modified setup will whence(prenominal) be comp bed.ObjectivesThe objectives of this discomb obulate is summ hoistd into four stages. In the first stage, the objective is to measure the hydraulic conductivity of the demesne using the standard TSB/Boutwell permeameter setup. The sec stage involves the modification of the standard TSB/Boutwell Permeameter setup. The aim is to obtain a simple installation setup which groundwork be easily and quickly installed in shallow boreholes for attendant testing.In the third stage, the objective is to test the modified TSB/Boutwell Permeameter test in the field. This is make by carrying out a series of tests in varied subterraneous media at the assigned site location. The results from both the standard and modified TSB/Boutwell Permeameter test will be comp bed.The last stage of the project consists of tinge coat depth psychology of the shit obtained from site. The results from the dickens setups will again be comp atomic number 18d to the hydraulic conductivity show ups obtained from the derivation of the Particle Size Distr ibution curves.The tasks that be by in this project includeThe review of TSB/Boutwell Permeameter methodology under create the modify TSB/Boutwell PermeameterCompletion of field tests using the TSB/Boutwell PermeameterCollection of soil hears and subsequent subatomic jot coat epitomeChapter 2 Literature Review2.1 Soil WaterSoils ar consists of discover substantiality pinpoints. The pore spaces mingled with the solid soupcons argon all interconnected which mean that weewee is free to hunt done these interconnected pore spaces (Whitlow, 2001). The weewee will accrue from a higher pore squelch shoot down to a lower pore pressure dit. The pressure of the pore peeing is measure relatively to the atmospheric pressure. The aim in which the pressure is zero (i.e. atmospheric) is de bookd as the piss table (Craig, 2004). The soil to a higher place the piddle table is assumed to be unsaturated and the soil to a lower place the pissing table is assumed to be ful ly saturated. The take of water table changes in relation with humour specifications and great deal also be unnatural by any constructional operations (Craig, 2004).It is usual to express a pressure as a pressure crack or query which is measurable in metres of water when considering water flow problems. According to Bernoullis equivalence, the sum up take aim at a point in flowing water groundwork be attached by the sum of three genius components pressure soul (u/w), velocity head (v2/2g) and elevation head (Z). This affinity is illustrated in the equation below(Equation 1)where h = total headu = pressurev = velocityg = speedup ascribable to gravityw = unit pitch of waterZ = elevation headHowever, since the seepage velocities in the soil are so small due to the high resistance to flow offered by the granular structure of the soil, the velocity head is often omitted from the equation (Whitlow, 2001). The total head at any point is because thunder mug be adequa tely represented by(Equation 2)In saturated conditions, the one-dimensional water flow in soil is governed by the Darcys legal philosophy, which states that the velocity of the groundwater flow is comparative to the hydraulic slope(Equation 3)where v = velocity of groundwater flow = flow/ ambit (q/A)k = coefficient of permeability or hydraulic conductivity (constant)i = hydraulic incline = head/length (h/L)The observational validity of Darcys Law matters firmly on the hydraulic conductivity, k, which must(prenominal) be cautiously de statusined so that it can represent the soil mass (Azizi, 2000). The different practical methods that can be used to measure the hydraulic conductivity will be discussed in Section 2.3.It is important to study the flow of water through porous media in soil mechanics. This is necessary for the assessment of underground seepage under assorted conditions, for investigation of problems involving the pumping of water for underground constructions, a nd for making stableness analyses of retaining structures that are subjected to seepage forces (Das, 2006).Hydraulic Conductivity (Coefficient of Permeability)Hydraulic conductivity, k, of a soil is the capacity of the soil to allow water to pass through it. The observe of hydraulic conductivity is often used to measure the resistance of a soil to water flow. Hydraulic conductivity has units of length divided by time. The most common unit used of measurement is meter per second (m/s). Although hydraulic conductivity has the same unit as those to describe velocity, it is non a measure of velocity (Coduto, 1999).Importance of Hydraulic ConductivityHydraulic conductivity is a in truth important parameter in geotechnical engineering or in ascertain the widespread of contaminant. This can be seen in the difficulties in quantity it. This is because hydraulic conductivity can varies from one point in a soil to a nonher, even with small changes in the soil singularitys. It is also, as mentioned in the forward section, influenced by the viscosity and unit weight of the fluid flowing through the soil. Hydraulic conductivity is also subordinate to the direction of flow which means that the vertical hydraulic conductivity would non be the same as the train hydraulic conductivity. This condition of the soil is said to be aeolotropic. Studies that deplete been made indicate that the value of vertical hydraulic conductivity (Kv) of a soil is usually higher than the horizontal hydraulic conductivity (Kh) in one or ii order of magnitude (Chen, 2000).Some applications in which information on hydraulic conductivity is very important are in modelling the groundwater flow and transferee of contaminants in the soil. Hydraulic conductivity data of a soil is also important for designing drainage of an area and in the construction of mankind dam and levee. In addition, it is very important in tackling most of the geotechnical problems such as seepage losses, settlement calculations, and stability analyses (Odong, 2007).Factors Affecting Hydraulic ConductivityThe hydraulic conductivity of a soil depends on many factors. The principal(prenominal) factor that affecting the value of hydraulic conductivity is the average coat of the pores mingled with portions in the soil, which in turn is related to the dissemination of particle sizes, particle shape and roughness, pore continuity, and soil structure (Craig,2004). In planetary the bigger the average size of the pores, the higher the value of hydraulic conductivity is.The value of hydraulic conductivity of a soil that has a heading of small percentages of fines will be significantly lower than the same soil without fines. In the other hand, the presence of fissures in clay will result in a much higher value of hydraulic conductivity compared to that of unfissured clay (Craig, 2004).The range of the hydraulic conductivity value is very large. board 1 below illustrates the range of hydraulic conductivity which differs from one soil type to another which is mainly due to the different average size of the pores between the soil particles.Table 1 Range of hydraulic conductivity values (m/s) with different soil type (Whitlow, 2001)102101110-1 find fault ridesVery nice drainage10-210-310-4Clean sandsGravel-sand mixtures10-510-6Very fine sandsSilts and silty sandsFissured and weathered claysGood drainage scummy drainage10-710-810-9Clay silts (20% clay)Unfissured claysPractically imperviousThe hydraulic conductivity is also interdependent to viscosity and density of water in which both are affected by temperature. It is so conclude that the value of hydraulic conductivity will indeed be affected by changes in temperature. Theoretically, it can be shown that for laminar flow and saturated soil condition the relationship between temperature and hydraulic conductivity(Equation 4)Where w= unit weight of water = viscosity of waterK = absolute coefficient (units m2). This valu e is dependent on the characteristic of the soil skeleton.Since most of the laboratory graduations were standardised at 20C, the value of hydraulic conductivity at this temperature is taken as 100% (Craig, 2004). some other value of hydraulic conductivity at 10C and 0C are 77% and 56% respectively (Craig, 2004).Hydraulic Conductivity TestsMost of the tests for standard hydraulic conductivity mensural one average value of hydraulic conductivity. However, some tests measured both the vertical and horizontal hydraulic conductivity values to obtained much dead on target estimation. There are numbers of experiments and test that can be done to measure the hydraulic conductivity of a soil. These tests to measure the hydraulic conductivity can be done both in the laboratory and in the field. The following sections will briefly discussed the most common laboratory and in-situ tests actd today to measure the hydraulic conductivity of a soil.Although with all the various tests develope d to measured the hydraulic conductivity, there are uncertainties arise on how the soils that world tested represent the whole soil condition at the site of interest. It is hence a good practice to suffice different tests and comparing the results obtained. science laboratory Permeability TestsOne problem with laboratory tests is that the examples serene do not adequately represent the fine conditions of the soil, e.g. fissures, joints or other characteristics in the site of interest. Even with carefully conducted tests and good try techniques, it is impossible to obtain a very absolute result. The results typically have a precision of about 50% or much than (Coduto, 1999). It is therefore important to take this into consideration if any construction activities or contamination remediation operations to be perform at the site of interest. unbroken percentage point Permeability TestThe constant head test is used to measure the hydraulic conductivity of to a greater extent pervious soils such as gravels and sands which have a hydraulic conductivity value of 10-4 m/s (Whitlow, 2001). The equipments used for this test is called a constant head permeameter. A schematic congresswoman of this equipment is shown in think 2.1.The constant head permeameter was developed base on the basic idea of Darcys Law (Equation 3). The soil type is contained in a cylinder of cross sectional area A. never-ending water supply is let to flow from a tank to the take in to accommodate a constant head. The water that flow through the warning is collected in a collection jar or container and the wipe out through the attempt is measured by calculating the batch of the water in the collection container over a period of time t.h aim 2.1 Schematic diagram of Constant Head Permeameter (www.geology.sdsu.edu)The hydraulic conductivity, k of the tested soil is then calculated byFrom equation 3(Equation 5)Where Q = the exempt through the sample (m3/s)L = the length of the s ample (m)A = cross-section of the sample (m2)h = hydraulic head (m)The in a higher place diagram shows a simple setup of the constant-head permeameter. other(a) setup is also on tap(predicate) which make use a pair of standpipes to measure the pore pressure and potential drop at twain points. This is illustrated in insert 2.2 below. Although both the setups are different, it makes used of the same concepts Darcys Law. build 2.2 Alternative setup of Constant Head Permeameter (Whitlow, 2001) fall Head Permeability TestThe go head test is used to measure the hydraulic conductivity of less permeable soils such as fine sands, silt and clay. The water flow resistance in these types of soil are very high which unable to measure unblemished measurements of hydraulic conductivity if used with constant head permeameter. Undisturbed samples are necessary to perform laboratory test to measure the hydraulic conductivity of a soil. However, a small degree of disturbance of the sample is evaluate as it is very hard to obtain a perfect tranquil sample. An undisturbed sample can be obtained usually using a U100 sample tube or a core-cutter tube (Whitlow, 2001).The schematic illustration of the falling head test setup is shown in Figure 2.3.Figure 2.3 Laboratory setup of falling head test (Whitlow, 2001)The sample is place in a cylinder container with a wire mesh and gravel drop at both end of the cylinder. The base of the cylinder is left wing to stand in a water reservoir fitted with a constant take aim overflow. At the other end, which is the top of the cylinder, it is connected to a spyglass standpipe of known diameter (Whitlow, 2001). These standpipes are then filled with de-aired water and it is allow to flow through the soil sample. The height of the water in the standpipe is measured at several time intervals. The test is then repeated using standpipes of different diameters.It is a good practice to take note of the sign and terminal unit weight and w ater content of the sample to move additional information about the properties of the sample (Whitlow, 2001). The hydraulic conductivity of the sample is then calculated from the results obtained from the tests. The Darcys Law concept is still used in determining the hydraulic conductivity. The derivation of the hydraulic conductivity for the falling head test is done as follow (Whitlow, 2001).Deriving from Equation 3With extension phone to Figure 2.3, if the level of the water in the standpipe fall dh in a time of dt the flow, q will beand the hydraulic gradient, i because(Equation 6)Where a = cross-sectional area of the standpipeA = cross-sectional area of the sampleWhen equation 6 is rearranged and integrated, the final equation to calculate the hydraulic conductivity is assumption as(Equation 7)Particle Size AnalysisParticle size outline is commonly used to classify the physical properties of the soil being tested. This testing method is used for both soil science and engin eering purposes (Keller and Gee, 2006). In context of engineering purposes, it is commonly used to define the particle size distributions of the soil. The data obtained from the particle size distributions can then be used to estimate the pore-size classes needed in calculating the hydraulic properties of the soil such as hydraulic conductivity (Keller and Gee, 2006).There are various methods of measuring particle size analysis. Traditional methods include sieving, hydrometer and pipette. other smart techniques are also been developed one example is laser-diffraction techniques (Eshel et al, 2004). However, particle size analysis is dependent on the technique used for shaping the particle size distribution. It is therefore a common practice to do much than one method to define the particle size distribution (Keller and Gee, 2006). The results from all the different methods can then be compared to obtain more vocalism result.For the traditional particle size analysis methods, c ardinal separate subroutines are used in order to obtain wider range of particles sizes (Head, 1980). The two procedures are sieving and sedimentation procedures (hydrometer or pipette method). Sieving is used to categorise large particle such as gravel and coarse sand. The particles can be stray into different size ranges using a series of standard sieves. For the fine particles such as silt and clay, sedimentation procedure is used (Head, 1980).in one case the particle size distribution is defined from the particle size analysis, the hydraulic conductivity of the tested soil can then be estimated using a number of established empirical equations. However, the applicability of the above equations depends on the type of soil that is being tested. The following paragraphs summarised several empirical equations from previous studies (Odong, 2007).Hazens equation(Equation 8)Kozeny-Carmans equation(Equation 9)Breyers equation(Equation 10)Slitchers equation(Equation 11)Where g = accel eration due to gravityv = kinematic viscosityn = porosity of the soild10 = cereal grass size in which 10% the sample is finer thanThe estimation of the hydraulic conductivity from these equations required information on the kinematic viscosity v and porosity n of the soil. The kinematic viscosity can be calculated by(Equation 12)Where = impulsive viscosity = density of waterThe porosity n can be calculated using the empirical relationship below(Equation 13)Where U is the coefficient of food texture uniformity and is given by(Equation 14)The values of d60and d10 can be obtained from the particle size distribution. d60and d10 represent the grain size for which 60% and 10% of the sample respectively is finer than.In-situ Field Permeability Tests cod to the problems associated with reliability and laboratory tests, as mention in Section 2.3.1, field methods of measuring the hydraulic conductivity should be used to obtain more accurate and reliable measurements. In the field test, t he soil disturbances is kept to a negligible level and they usually involves the testing of larger, more representative samples. Although, in term of cost and time, field measurement method is more expensive, it will as well provide more reliable measurement of hydraulic conductivity when dealing with a wide range of soil macro-structural characteristics. Other more economic option of field measurement can also be done. Such example is by performing borehole test, provided the pumping observation sequences are carefully planned and controlled (Whitlow, 2001).Well Pumping TestsThis method is more suitable if used to measure hydraulic conductivity in homogenised coarse soil strata (Craig, 2004). The procedure involves the measurement of water that is being pumped out of a well at a constant rate, then observing the frame of these pumping activities to the drawdown of the groundwater level at other wells. The diameter of the well is normally at least 300mm and penetrates to the bott om of the stratum under test (Craig, 2004). The pumping rate and the groundwater levels in two or more supervise wells are then recorded. The analysis of the results depends whether the aquifer is moderate or unimprisoned.Well pumping test in a confined aquiferIn confined aquifer the permeable stratum is squeezed in between two water-resistant points. This is illustrated in Figure 2.4 below. To perform the test, the pumping rate must not be too high to reduce the level in the pumping well below the top of the aquifer. The interface between the top aquifer and the overlying impermeable stratum therefore forms the top stream line (Whitlow, 2001).Figure 2.4 Pumping test in confined aquifer (Azizi, 2000)Figure 2.4 illustrates the arrangement of the pumping well and two other monitoring wells. Two assumptions were made at this point the piezometric show is above the upper come of the aquifer and the hydraulic gradient is constant at a given radius (Whitlow, 2001). In unbendable state condition, the hydraulic gradient through an elemental cylinder with radius r from the well centres estimated as followwhere dr = thicknessh = heightThe area in which the water flow, Awhere D = the thickness of the aquiferSubstituting the area A into the Darcys Law (Equation 4) will giveHenceAnd therefore the hydraulic conductivity is(Equation 15)In the case that the piezometric level is above ground level, where the water level intimate the well inserted into the confined aquifer rises above the ground level, this scenario is called Artesian conditions (Azizi, 2000). This is illustrated in Figure 2.5.Figure 2.5 Artesian conditions (Azizi, 2000)Well pumping test in unimprisoned aquiferAn unconfined aquifer is a free-draining surface layer that allows water to flow through the surface. The permeable stratum is not overlain by an impermeable layer. The piezometric surface is therefore in the same level of the water table. This is illustrated in Figure 2.6 below. The surface lay er permeability is very high, thus allowing the water table to quiver up and down easily.Figure 2.6 Pumping test in an unconfined aquifer (Whitlow, 2001) downstairs steady state pumping conditions, the hydraulic gradient i at a given radius is assumed to be constant in a homogenous media. Homogenous unit is where the properties at any location are the same. For instance, sandstone has grain size distribution, porosity and thickness variation in spite of appearance a very small limit (Fetter, 2001). With reference to the arrangement of pumping well and two monitoring wells in Figure 2.6 above, the hydraulic conductivity can be go through byDeriving from Equation 3whereHydraulic gradient i isAnd area through which the water flow,Then,Thus, hydraulic conductivity for an unconfined aquifer (after integrating the above equation) is(Equation 16)Borehole Permeameter TestsThere are many borehole tests developed to determine the hydraulic conductivity of a soil. The most common in-situ bo rehole tests are as follow lick testTwo-stage borehole test/ Boutwell Permeameter uncertain head testIn-situ constant head testSlug test is one of the cheapest in-situ field methods to determine the hydraulic conductivity of a soil. The procedure of this test involves the rapid adding or removing a slug or water into a monitoring well. The slug can be of anything that can displace the volume of the water in the well, e.g. water, plastic underground crest at both ends, and other material of known volume and can fit into the monitoring well. The rate of rise and fall of the groundwater level is then observed until it reaches an equilibrium state.In a variable head test, a slug is introduced into the monitoring well by either adding in a measured volume of water into the well or other materials mentioned earlier. The rate of water level fall is then measured in time. This is called falling head test. The water can also be aloof out from the well by using a bailer or a pump. The rat e of water level rise is then measured with time. This is called a arise head test. Depending on the properties of the aquifer and the soil, and the size of the slug used the water can either returns to its original water level before the test quickly or very slowly. For instance, if the porosity of the soil is high then the water level will returns very quickly to its original water level before the test is done.There is also the constant head test. In this test the water level or head is maintain passim the test at a given level. This is done by adjusting and measuring the flow rate of the water at intervals from start to the end of the test (Whitlow, 2001). The constant head test is said to give more accurate results, provided the water pressure is controlled so that it would not cause fracturing or other disturbance to the soil (Whitlow, 2001). There are several assumptions made for this testThe soil is homogenous, isotropic, uniformly soakedInfinite boundariesSoil does not squire when wettedThe expressions use to calculate the hydraulic conductivity for the above tests depend on whether the stratum is unconfined or unconfined, the position of the bottom of the example within the stratum and details of the drainage face in the soil (Craig, 2004). The horizontal hydraulic conductivity is tend to be measured if the soil is anisotropic with respect to permeability and if the borehole extends below the bottom of the casing. On the other hand, the vertical hydraulic conductivity is often measured if the casing penetrates below soil level in the bottom of the borehole (Craig, 2004). The following expressions are all recommended in BS 5930 to calculate the hydraulic conductivity (Whitlow, 2001).For variable head test(Equation 17)Or,(Equation 18)For constant head testHvorslevs time lag analysis(Equation 19)Gibsons root-time method(Equation 20)where A20% clay)Unfissured claysPractically imperviousThe hydraulic conductivity is also dependent to viscosity and de nsity of water in which both are affected by temperature. It is therefore conclude that the value of hydraulic conductivity will then be affected by changes in temperature. Theoretically, it can be shown that for laminar flow and saturated soil condition the relationship between temperature and hydraulic conductivity(Equation 4)Where w= unit weight of water = viscosity of waterK = absolute coefficient (units m2). This value is dependent on the characteristic of the soil skeleton.Since most of the laboratory graduations were standardised at 20C, the value of hydraulic conductivity at this temperature is taken as 100% (Craig, 2004). Other value of hydraulic conductivity at 10C and 0C are 77% and 56% respectively (Craig, 2004).Hydraulic Conductivity TestsMost of the tests for measuring hydraulic conductivity measured one average value of hydraulic conductivity. However, some tests measured both the vertical and horizontal hydraulic conductivity values to obtained more accurate estimati on. There are numbers of experiments and test that can be done to measure the hydraulic conductivity of a soil. These tests to measure the hydraulic conductivity can be done both in the laboratory and in the field. The following sections will briefly discussed the most common laboratory and in-situ tests practiced today to measure the hydraulic conductivity of a soil.Although with all the various tests developed to measured the hydraulic conductivity, there are uncertainties arise on how the soils that being tested represent the whole soil condition at the site of interest. It is therefore a good practice to perform different tests and comparing the results obtained.Laboratory Permeability TestsOne problem with laboratory tests is that the samples collected do not adequately represent the detailed conditions of the soil, e.g. fissures, joints or other characteristics in the site of interest. Even with carefully conducted tests and good sampling techniques, it is impossible to obtain a very accurate result. The results typically have a precision of about 50% or more (Coduto, 1999). It is therefore important to take this into consideration if any construction activities or contamination remediation operations to be perform at the site of interest.Constant Head Permeability TestThe constant head test is used to measure the hydraulic conductivity of more permeable soils such as gravels and sands which have a hydraulic conductivity value of 10-4 m/s (Whitlow, 2001). The equipments used for this test is called a constant head permeameter. A schematic illustration of this equipment is shown in Figure 2.1.The constant head permeameter was developed base on the basic idea of Darcys Law (Equation 3). The soil sample is contained in a cylinder of cross-sectional area A. Continuous water supply is let to flow from a tank to the sample to maintain a constant head. The water that flow through the sample is collected in a collection jar or container and the discharge through the sample is measured by calculating the volume of the water in the collection container over a period of time t.hFigure 2.1 Schematic diagram of Constant Head Permeameter (www.geology.sdsu.edu)The hydraulic conductivity, k of the tested soil is then calculated byFrom equation 3(Equation 5)Where Q = the discharge through the sample (m3/s)L = the length of the sample (m)A = cross-section of the sample (m2)h = hydraulic head (m)The above diagram shows a simple setup of the constant-head permeameter. Other setup is also available which make use a pair of standpipes to measure the pore pressure and potential at two points. This is illustrated in Figure 2.2 below. Although both the setups are different, it makes used of the same concepts Darcys Law.Figure 2.2 Alternative setup of Constant Head Permeameter (Whitlow, 2001)Falling Head Permeability TestThe falling head test is used to measure the hydraulic conductivity of less permeable soils such as fine sands, silt and clay. The water f low resistance in these types of soil are very high which unable to measure accurate measurements of hydraulic conductivity if used with constant head permeameter. Undisturbed samples are required to perform laboratory test to measure the hydraulic conductivity of a soil. However, a small degree of disturbance of the sample is accepted as it is very hard to obtain a perfect undisturbed sample. An undisturbed sample can be obtained usually using a U100 sample tube or a core-cutter tube (Whitlow, 2001).The schematic illustration of the falling head test setup is shown in Figure 2.3.Figure 2.3 Laboratory setup of falling head test (Whitlow, 2001)The sample is place in a cylinder container with a wire mesh and gravel filter at both end of the cylinder. The base of the cylinder is left to stand in a water reservoir fitted with a constant level overflow. At the other end, which is the top of the cylinder, it is connected to a glass standpipe of known diameter (Whitlow, 2001). These standp ipes are then filled with de-aired water and it is allow to flow through the soil sample. The height of the water in the standpipe is measured at several time intervals. The test is then repeated using standpipes of different diameters.It is a good practice to take note of the initial and final unit weight and water content of the sample to get additional information about the properties of the sample (Whitlow, 2001). The hydraulic conductivity of the sample is then calculated from the results obtained from the tests. The Darcys Law concept is still used in determining the hydraulic conductivity. The derivation of the hydraulic conductivity for the falling head test is done as follow (Whitlow, 2001).Deriving from Equation 3With reference to Figure 2.3, if the level of the water in the standpipe fall dh in a time of dt the flow, q will beand the hydraulic gradient, iTherefore(Equation 6)Where a = cross-sectional area of the standpipeA = cross-sectional area of the sampleWhen equation 6 is rearranged and integrated, the final equation to calculate the hydraulic conductivity is given as(Equation 7)Particle Size AnalysisParticle size analysis is commonly used to classify the physical properties of the soil being tested. This testing method is used for both soil science and engineering purposes (Keller and Gee, 2006). In context of engineering purposes, it is commonly used to define the particle size distributions of the soil. The data obtained from the particle size distributions can then be used to estimate the pore-size classes needed in calculating the hydraulic properties of the soil such as hydraulic conductivity (Keller and Gee, 2006).There are various methods of measuring particle size analysis. Traditional methods include sieving, hydrometer and pipette. Other new techniques are also been developed one example is laser-diffraction techniques (Eshel et al, 2004). However, particle size analysis is dependent on the technique used for defining the particle si ze distribution. It is therefore a common practice to do more than one method to define the particle size distribution (Keller and Gee, 2006). The results from all the different methods can then be compared to obtain more representative result.For the traditional particle size analysis methods, two separate procedures are used in order to obtain wider range of particles sizes (Head, 1980). The two procedures are sieving and sedimentation procedures (hydrometer or pipette method). Sieving is used to categorise large particle such as gravel and coarse sand. The particles can be separated into different size ranges using a series of standard sieves. For the finer particles such as silt and clay, sedimentation procedure is used (Head, 1980).Once the particle size distribution is defined from the particle size analysis, the hydraulic conductivity of the tested soil can then be estimated using a number of established empirical equations. However, the applicability of the above equations d epends on the type of soil that is being tested. The following paragraphs summarised several empirical equations from previous studies (Odong, 2007).Hazens equation(Equation 8)Kozeny-Carmans equation(Equation 9)Breyers equation(Equation 10)Slitchers equation(Equation 11)Where g = acceleration due to gravityv = kinematic viscosityn = porosity of the soild10 = grain size in which 10% the sample is finer thanThe estimation of the hydraulic conductivity from these equations required information on the kinematic viscosity v and porosity n of the soil. The kinematic viscosity can be calculated by(Equation 12)Where = dynamic viscosity = density of waterThe porosity n can be calculated using the empirical relationship below(Equation 13)Where U is the coefficient of grain uniformity and is given by(Equation 14)The values of d60and d10 can be obtained from the particle size distribution. d60and d10 represent the grain size for which 60% and 10% of the sample respectively is finer than.In-situ Field Permeability TestsDue to the problems associated with reliability and laboratory tests, as mention in Section 2.3.1, field methods of measuring the hydraulic conductivity should be used to obtain more accurate and reliable measurements. In the field test, the soil disturbances is kept to a minimum level and they usually involves the testing of larger, more representative samples. Although, in term of cost and time, field measurement method is more expensive, it will as well provide more reliable measurement of hydraulic conductivity when dealing with a wide range of soil macro-structural characteristics. Other more economic option of field measurement can also be done. Such example is by performing borehole test, provided the pumping observation sequences are carefully planned and controlled (Whitlow, 2001).Well Pumping TestsThis method is more suitable if used to measure hydraulic conductivity in homogenous coarse soil strata (Craig, 2004). The procedure involves the measure ment of water that is being pumped out of a well at a constant rate, then observing the effect of these pumping activities to the drawdown of the groundwater level at other wells. The diameter of the well is normally at least 300mm and penetrates to the bottom of the stratum under test (Craig, 2004). The pumping rate and the groundwater levels in two or more monitoring wells are then recorded. The analysis of the results depends whether the aquifer is confined or unconfined.Well pumping test in a confined aquiferIn confined aquifer the permeable stratum is squeezed in between two impermeable layers. This is illustrated in Figure 2.4 below. To perform the test, the pumping rate must not be too high to reduce the level in the pumping well below the top of the aquifer. The interface between the top aquifer and the overlying impermeable stratum therefore forms the top stream line (Whitlow, 2001).Figure 2.4 Pumping test in confined aquifer (Azizi, 2000)Figure 2.4 illustrates the arrangem ent of the pumping well and two other monitoring wells. Two assumptions were made at this point the piezometric surface is above the upper surface of the aquifer and the hydraulic gradient is constant at a given radius (Whitlow, 2001). In steady state condition, the hydraulic gradient through an elemental cylinder with radius r from the well centres estimated as followwhere dr = thicknessh = heightThe area in which the water flow, Awhere D = the thickness of the aquiferSubstituting the area A into the Darcys Law (Equation 4) will giveHenceAnd therefore the hydraulic conductivity is(Equation 15)In the case that the piezometric level is above ground level, where the water level inside the well inserted into the confined aquifer rises above the ground level, this scenario is called Artesian conditions (Azizi, 2000). This is illustrated in Figure 2.5.Figure 2.5 Artesian conditions (Azizi, 2000)Well pumping test in unconfined aquiferAn unconfined aquifer is a free-draining surface layer that allows water to flow through the surface. The permeable stratum is not overlain by an impermeable layer. The piezometric surface is therefore in the same level of the water table. This is illustrated in Figure 2.6 below. The surface layer permeability is very high, thus allowing the water table to fluctuate up and down easily.Figure 2.6 Pumping test in an unconfined aquifer (Whitlow, 2001)Under steady state pumping conditions, the hydraulic gradient i at a given radius is assumed to be constant in a homogenous media. Homogenous unit is where the properties at any location are the same. For instance, sandstone has grain size distribution, porosity and thickness variation within a very small limit (Fetter, 2001). With reference to the arrangement of pumping well and two monitoring wells in Figure 2.6 above, the hydraulic conductivity can be determine byDeriving from Equation 3whereHydraulic gradient i isAnd area through which the water flow,Then,Thus, hydraulic conductivity for a n unconfined aquifer (after integrating the above equation) is(Equation 16)Borehole Permeameter TestsThere are many borehole tests developed to determine the hydraulic conductivity of a soil. The most common in-situ borehole tests are as followSlug testTwo-stage borehole test/ Boutwell PermeameterVariable head testIn-situ constant head testSlug test is one of the cheapest in-situ field methods to determine the hydraulic conductivity of a soil. The procedure of this test involves the rapid adding or removing a slug or water into a monitoring well. The slug can be of anything that can displace the volume of the water in the well, e.g. water, plastic tubing capped at both ends, and other material of known volume and can fit into the monitoring well. The rate of rise and fall of the groundwater level is then observed until it reaches an equilibrium state.In a variable head test, a slug is introduced into the monitoring well by either adding in a measured volume of water into the well or other materials mentioned earlier. The rate of water level fall is then measured in time. This is called falling head test. The water can also be removed out from the well by using a bailer or a pump. The rate of water level rise is then measured with time. This is called a rising head test. Depending on the properties of the aquifer and the soil, and the size of the slug used the water can either returns to its original water level before the test quickly or very slowly. For instance, if the porosity of the soil is high then the water level will returns very quickly to its original water level before the test is done.There is also the constant head test. In this test the water level or head is maintained throughout the test at a given level. This is done by adjusting and measuring the flow rate of the water at intervals from start to the end of the test (Whitlow, 2001). The constant head test is said to give more accurate results, provided the water pressure is controlled so that it would not cause fracturing or other disturbance to the soil (Whitlow, 2001). There are several assumptions made for this testThe soil is homogenous, isotropic, uniformly soakedInfinite boundariesSoil does not swell when wettedThe expressions use to calculate the hydraulic conductivity for the above tests depend on whether the stratum is unconfined or unconfined, the position of the bottom of the casing within the stratum and details of the drainage face in the soil (Craig, 2004). The horizontal hydraulic conductivity is tend to be measured if the soil is anisotropic with respect to permeability and if the borehole extends below the bottom of the casing. On the other hand, the vertical hydraulic conductivity is often measured if the casing penetrates below soil level in the bottom of the borehole (Craig, 2004). The following expressions are all recommended in BS 5930 to calculate the hydraulic conductivity (Whitlow, 2001).For variable head test(Equation 17)Or,(Equation 18)For cons tant head testHvorslevs time lag analysis(Equation 19)Gibsons root-time method(Equation 20)where A