Permeating partially hydrated GCLs with jet fuel at temperatures from 208C and 208C

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1 Permeating partially hydrated GCLs with jet fuel at temperatures from 208C and 208C R. K. Rowe 1, P. Hurst 2 and T. Mukunoki 3 1 Professor and Vice-Principal of Research, GeoEngineering Centre at Queen s - RMC, Kingston, Canada, Telephone: , Telefax: ; kerry@civil.queensu.ca 2 Environmental Division, Golder Associates Ltd, 32 Steacie Drive, Kanata, Ontario K2K 2A9, Canada, Telephone: , Telefax: , paul_hurst@golder.com 3 Associate Research Director, GeoEngineering Centre at Queen s - RMC, Kingston, Canada, Telephone: , Telefax: , toshifumi@ce.queensu.ca Received 16 February 2005, revised 15 July 2005, accepted 1 September 2005 ABSTRACT: The hydraulic conductivity of hydrated and partially hydrated geosynthetic clay liners (GCLs) with respect to Jet Fuel A-1 (Arctic diesel) is examined at 208C, 58C, 58C, and 208C. Methods developed to hydrate GCLs to specific water contents (60%, 90%, 120%) and subject them to subzero temperatures without the additional uptake of water are described. Results indicate that there are two main mechanisms that affect the hydraulic conductivity of Jet Fuel A-1. For a constant bulk void ratio, as the water content increases, the hydraulic conductivity with respect to Jet Fuel A-1 decreases. Similarly, for a constant water content, as bulk void ratio decreases, the hydraulic conductivity with respect to Jet Fuel A-1 decreases. GCLs at positive temperatures with an initial degree of saturation (S r ) greater then 0.77 had a hydraulic conductivity with respect to Jet Fuel A-1 of less than 10 9 m/s, whereas GCLs at subzero temperatures with S r. 0:70 had a hydraulic conductivity with respect to Jet Fuel A-1 of less than 2: m=s. Highly saturated (S r. 0:85) GCLs at subzero temperatures were essentially impermeable, having a hydraulic conductivity with respect to Jet Fuel A-1 of less than m/s. KEYWORDS: Geosynthetics, Geosynthetic clay liner, Jet fuel, Hydrocarbons, Hydraulic conductivity, Subzero temperatures RERERENCE: Rowe, R. K., Hurst, P. & Mukunoki, T. (2005). Permeating partially hydrated GCLs with jet fuel at temperatures from 208C and 208C. Geosynthetics International, 12, No. 6, INTRODUCTION Geosynthetic clay liners (GCLs) have gained widespread use in landfill covers and growing acceptance for use in composite base liners for landfills. There are also growing applications as secondary containment for chemicals (e.g. to contain spills). There is relatively little experience with their use for containment of hydrocarbons over significant periods of time (years). However, one field trial (Li et al. 2002) has illustrated how a GCL can be used as part of a composite containment system for the containment of hydrocarbons in the Arctic. This paper aims to address a number of issues related to this novel application for GCLs. For GCLs to perform their design function well, it is necessary for the bentonite part of the liner to be sufficiently hydrated with water prior to contact with contaminants. While some work has been done regarding the hydraulic conductivity (permeability) of saturated GCLs at room temperatures and non-standard permeants (Daniel et al. 1993; Petrov and Rowe 1997), little had # 2005 Thomas Telford Ltd been done to investigate the hydraulic conductivity of partially saturated GCLs to non-standard permeants. In particular, there is a need to know the degree of saturation required for the GCL to perform well as an advective barrier to hydrocarbons. Furthermore, owing to the evolving use for GCLs in cold climates, it is important to understand how well a GCL will perform as a barrier to contaminants in subzero temperature conditions. Thus the objectives of this paper are twofold: first, to assess the hydraulic conductivity of unsaturated GCLs with respect to Jet Fuel A-1; second, to assess the effects of temperature on hydraulic conductivity with respect to Jet Fuel A-1, and in particular to assess the degree of saturation required to give low hydraulic conductivities at temperatures between 20 and 208C. 2. PREVIOUS STUDIES Although work has been done on permeating GCLs with non-standard permeants at room temperatures, little has 333

2 334 Rowe et al. been done on permeating GCLs with Jet Fuel A-1 at room temperature or freezing temperatures. The following sections describe what work has been conducted in this area Hydrocarbon permeation at non-freezing temperatures: previous studies Brown et al. (1984) and Foreman and Daniel (1986) concluded that permeation of soil by organic fluids could cause a change in the soil structure. Brown et al. (1984) evaluated the hydraulic conductivity of kaolinite, mica, and bentonite using a fixed-wall permeameter. They permeated several different pure hydrocarbons (kerosene, paraffin oil, diesel oil, gasoline, and motor oil) through the bentonite at three different hydraulic gradients, and found that the hydraulic conductivity of clayey soils to pure hydrocarbons was 1 4 orders of magnitude higher than that of water. Foreman and Daniel (1986) examined the effect of hydraulic gradient and type of permeameter (flexible or fixed wall) on the hydraulic conductivity of compacted clay to the permeants methanol and heptane. They found that permeation of the organic permeants caused the clay to shrink and produce cracks or micropores. At low confining pressures sidewall leaks developed in the fixed-wall permeameter during organic fluid permeation. Daniel et al. (1993) permeated unsaturated GCLs with hydrocarbons (benzene, gasoline, methanol, tert-butylethylether (MTBE), trichloroethylene (TCE)) using a flexiblewall permeameter, and found that for gravimetric water contents, 50% the bentonite part of the GCL was very permeable (k 10 7 m/s). However, for gravimetric water contents greater than 100%, the hydraulic conductivity was very low (k, m/s). Petrov and Rowe (1997) and Petrov et al. (1997) used a rigid-wall permeameter to examine the hydraulic conductivity of hydrated GCLs permeated with water, salt water ( M NaCl), and ethanol (25%, 50%, 75%, 100%). Samples were hydrated with distilled de-ionized water using a hydration head pressure of 2 4 cm, and permeated using hydraulic gradients for Tests were completed using confining stresses of 3, 6, 25, 50, 75, 100, 150, 200, and 400 kpa. They found that for low concentrations of ethanol (, 50%) the hydraulic conductivity was less than that for water owing to viscosity effects, and for high concentrations (.75%) the hydraulic conductivity was higher than that of water owing to diffuse double-layer contractions caused by the ethanol. Shan and Lai (2002) hydrated GCLs for 2 to 7 days using different liquids (de-ionized distilled water, tap water, landfill leachate, ph 5.0 acid water) consecutively. They used a flexible-wall permeameter with a head difference of 13.8 kpa and effective stress of 34.5 kpa, and found that gasoline could not permeate a saturated water-permeated GCL (Bentomat 1 ST and Claymax 1, both with 3.6 kg/m 2 bentonite) at gradients of less than 150. Fernandez and Quigley (1985) used a rigid-wall permeameter with a flow rate of ml/s and found that the hydraulic conductivity of clayey soils is strongly influenced by the physicochemical properties (dielectric constant) of the permeating hydrocarbons (benzene, cyclohexane, xylene). They created several clayey soil samples, each mixed with a different liquid, and compacted to a predefined void ratio, to examine the effect of mixing the clay with fluids having a range of dielectric constants (from 2 to 80) and then permeating with the same fluid. They measured an increase of hydraulic conductivity from to m/s as the dielectric constant of the chemical decreased from 80 to 2. In addition, they found that sequential permeation of compacted water wet samples showed no change in hydraulic conductivity (k m/s) when permeated with water-insoluble hydrocarbons. Boldt-Leppin et al. (1996) examined the permeation of diesel fuel through mesh graded Ottawa sand Wyoming Na-bentonite (CS-50) samples and found that for high percentages of bentonite ( 15%), the hydraulic conductivity with respect to diesel ranged between and m/s. Yang and Lo (2004) permeated 10 cm diameter samples using an apparatus similar to a flexible-wall permeameter with a confining pressure of 70 kpa (pressure difference across the GCL 350 kpa), and reported a hydraulic conductivity of 10 8 m/s for pure bentonite compacted 2 4% wet of optimum and permeated with gasoline. Rowe et al. (2004) permeated needle-punched GCLs subjected to freeze thaw cycles with respect to Jet Fuel A-1 at room temperature (21 18C) and reported no significant impact on the hydraulic conductivity with respect to jet fuel for up to 13 freeze thaw cycles Hydrocarbon permeation at subzero temperatures: previous studies There has been very little research on the permeation of hydrocarbons through frozen bentonite. Wiggert et al. (1997) permeated pure decane (a nonaqueous phase liquid) through gravelly sands and found a linear correlation between intrinsic permeability and ice saturation, varying from m 2 at 0% ice saturation to nearly negligible levels at 100% ice saturation. With the addition of bentonite prior to freezing, hydraulic conductivity was reduced to negligible (according to Wiggert et al. 1997) levels. McCauley et al. (2000) permeated a Jet A-50 fuel mixture through organic rich silty sand and found that hydraulic conductivity decreased as ice saturation increased. The information presented above suggests that bentonite can be an effective advective barrier to hydrocarbons when sufficiently saturated prior to contact with contaminants. 3. TESTING PROGRAM A series of fixed-wall tests were performed on GCLs hydrated to different degrees of saturation and permeated with Jet Fuel A-1 at different temperatures. The methods used, apparatus, and procedures are described in the following subsections Geosynthetic clay liner (GCL) The GCL used was a nonwoven, needle-punched, scrimreinforced thermally treated product (BENTOFIX 1 FIX-

3 Permeating partially hydrated GCLs with jet fuel at temperatures from 208C and 208C NWL), with basic properties given in Table 1. Granular sodium bentonite was encapsulated between a scrimreinforced nonwoven and a virgin staple fiber nonwoven geotextile. Other significant properties listed by the manufacturer are: a nominal hydraulic conductivity of m/s (ASTM D 5084); internal shear strength of 24 kpa (ASTM D 5321); a minimum bentonite swell index of 24 ml/2g (ASTM D 5890); and a peel strength of 66N (ASTM D 4632) Jet Fuel A-1 Jet Fuel A-1 is a colorless to pale yellow liquid, with a kerosene-like or petroleum odor, that is widely used in the northern regions. Physical data on Jet Fuel A-1 are limited, but according to its Material Safety Data Sheet (MSDS), the freezing point is below 478C, and the specific gravity at 158C ranges from to depending on the specific composition. For these tests, one type of Jet Fuel A-1 was used to eliminate this variability. Its solubility in water is approximately 5 mg/l, and its kinematic viscosity is 8.0 mm 2 /s at 208C Apparatus The hydraulic conductivity with respect to Jet Fuel A-1 testing was completed using a constant-flow, fixed-wall permeameter (also called a fixed-ring permeameter) similar to the apparatus described by Petrov and Rowe (1997). The fixed-wall apparatus was chosen for this testing because it allows testing at higher hydraulic gradients than the flexible-wall permeameter. Pore volumes can be passed through the sample more quickly, and pressure equalization can be achieved in a matter of months as opposed to years with the flexible-wall permeameter. The fixed-wall apparatus was constructed from stainless steel. Porous disks were constructed from Teflon 1, and all seals were Viton 1 rubber to avoid chemical compatibility issues and allow Jet Fuel A-1 to be used as a permeant. In order to maintain a high degree of temperature control, the test cells were placed inside a freezer retrofitted with an accurate thermostat, and the freezer was placed inside a cold room. The remainder of the apparatus was placed beside the freezer in the cold room, and the freezer and cold room were both set at the same temperature. Using this double buffer set-up, it was possible to maintain a temperature control of 0.58C as the samples were permeated. A pressure transducer was used to measure the influent pressure for each cell. The pressure transducers used could measure up to 1380 kpa (200 psi) with a precision of V (0.86 kpa). The hydraulic gradient was deduced from the known flow and hydraulic conductivity with respect to Jet Fuel A-1 using Darcy s Law. Figure 1 shows a schematic of the test set-up Sample preparation and installation Tests were performed on GCLs at a number of predetermined water contents. In order to achieve the desired water contents for each sample, the following sample preparation procedure was developed. First, the GCL was carefully cut using a 54 mm diameter steel cutting shoe. The mass of the GCL and cutter was measured and, knowing the mass of the cutter, the GCL sample mass was deduced. This mass was checked against the calculated average to ensure a high degree of consistency in the mass of samples tested. Any samples falling outside the desired range were discarded. To allow removal of the GCL from the cutter without the loss of any powdered bentonite, a small bead of water was spread around the outside diameter of the cutter. As the sample was slowly removed, the bentonite at the edges absorbed the water and created a seal around the edges of the sample. Finally, the GCL sample was placed in the fixed-wall permeameter, with a saturated stone porous disk and a dry porous Teflon disk on the bottom and top of the GCL, respectively. Filter papers were used above and below the GCL. One large central spring (spring constant 4.54 N/mm) was inserted GCL sample Scale Displacement transducer 5 cm Air bleed valve Compression spring Teflon porous disk Effluent bottle Pressure transducer Stainless steel piping Figure 1. Schematic of hydraulic conductivity test set-up Cylinder Table 1. Mass per unit area a of GCL components Specified values (g/m 2 ) Mean measured values (g/m 2 ) Cover layer 200 MARV b 237 (SD: c 33.3) Bentonite layer 3660 MARV b 4808 (SD: c 406) Carrier layer 200 MARV b 245 (SD: c 6.8) a ASTM D b Minimum Average Roll Value. c Standard deviation.

4 336 Rowe et al. into the cell to provide a confining stress of approximately 14 kpa. Because the sample thickness affected the spring force applied, and hence the confining stress applied, the value of 14 kpa was approximate. In actuality, confining stress varied from around 12 kpa (for a dry sample) to 16 kpa (for a fully water-saturated sample). It is not expected that these small changes would have a significant effect on the results presented. Knowing the mass of the GCL sample and the mass of water used in sample preparation, the amount of de-ionized distilled water needed to reach the target water content was calculated and added. Given the hydrophobic nature of the cover and carrier geotextile, and the high swelling capacity of the bentonite, it was assumed that any added water contributed to the bentonite water content. Furthermore, by measuring the thickness of the GCL and using relationships developed by Petrov and Rowe (1997), it was possible to correlate the bulk void ratio and degree of saturation. After a prescribed time of 24 h the cell was opened, and the stone porous disk replaced with another Teflon porous disk so as to stop the further uptake of water from the porous disk into the GCL. The cell was resealed and the sample allowed to equilibrate for 7 days at either 58C or 208C before testing began Scanning electron microscope (SEM) sample preparation The process used was based on Goldstein et al. (1992). To prepare the bentonite samples for SEM analysis, a small (1 cm 3 1 cm) square was cut from a GCL and a utility knife blade was inserted a few millimeters into the bentonite. A cup filled with pentane (freezing point 1278C) was cooled using a liquid nitrogen bath. The sample was freeze-dried in the pentane and the utility blade tapped with a hammer to create a fracture in the bentonite. Finally, the sample was put into a strong vacuum for 24 h to sublime and remove the frozen water and Jet Fuel A-1, leaving the sample dry. It was assumed that the fracture created was as close to the undisturbed pore structure as possible, and was where the SEM images were taken from Testing procedure When samples were ready for testing, the cells were filled with the permeant, and all lines were flushed to remove all air. The cells were closed and permeation began at a typical constant flow rate of 2.88 ml/day ( m 3 / m 2 /s). The flow rate was chosen because it allowed tests to complete in a reasonable amount of time. Furthermore, Mukunoki et al. (2003) used a similar flow rate, and so the same flow rate allowed comparison and validation of data between these two research programs. Tests were run until the pressure equalized (assumed chemical equilibrium), which typically took 2 5 months depending on the permeant. Table 2 summarizes the gradients observed during the tests. 4. RESULTS Tests were conducted at 58C, 208C, 58C and 208C for a range of controlled GCL water contents (Table 3). Although care was taken to select GCL samples with a mass per unit area that fell within a predetermined range, there is considerable variability in the mass of bentonite, although the manufacturer s specified minimum value (3,660 g/m 2 ) was always exceeded (Table 1), and the mean was more than 1000 g/m 2 above the specified value (with a standard deviation of 406 g/m 2 ) Hydraulic conductivity of Jet Fuel A-1 at nonfreezing temperatures One objective of this research was to estimate the minimum degree of saturation required for the GCLs to perform well as an advective barrier to Jet Fuel A-1. Following completion of a test, the samples were carefully removed from the cells and a qualitative evaluation of the seal between the sample and the cell wall was performed. The samples were carefully cut in half to examine the texture of the bentonite and water distribution. Table 4 summarizes the observations for samples with different initial degrees of saturation. In addition, Figure 2 and Figure 3 show the typical texture of the bentonite inside the GCL at test completion. These observations suggest that a minimum degree of saturation of 0.77 is needed for the GCLs to perform well as an advective barrier to Jet Fuel A-1. The results of tests conducted at 208C are shown in Figure 4. It can be seen that the hydraulic conductivity with respect to Jet Fuel A-1 decreases as water content increases. As the water content increases from 60% to 120% there is more water present in the sample, more swelling during hydration, and a lower hydraulic conductivity with respect to Jet Fuel A-1. The four samples with a hydraulic conductivity of the order of 10 8 m/s all had an intact side wall (and hence no leakage) at test completion, but during the test very little pressure developed in the system (so little that it could not be accurately measured), indicating a high hydraulic conductivity. To get a lower bound to the hydraulic conductivity with respect to Jet Fuel A-1, the value of approximately m/s was calculated based on the sample thickness and the minimum pressure that the data acquisition could accurately measure. Tests were conducted to examine the effects of applied Table 2. Final gradients across GCL samples Degree of saturation Range in final hydraulic gradients, i Test temperature 0.60, S r, to 50 58C and 208C S r to C and 208C 0.60, S r, to C

5 Permeating partially hydrated GCLs with jet fuel at temperatures from 208C and 208C 337 Table 3. Summary of tests conducted Test series Temperature, T (8C) No. of samples Gravimetric water content (%) Degree of saturation, S r Sequence of test events Samples permeated with water at 208C , 0.70, 0.81, Samples permeated with Jet Fuel A-1 at 208C , 0.74, 0.89, , 0.64, , 0.73, , 1 1. Samples permeated with Jet Fuel A-1 at 208C and and , 119, 124, 124, 126, 131, 142, 154 a Sidewall leakage during testing, data point disregarded. b Maximum pressure developed during testing (k, m/s). c Cell plugged with ice, data point disregarded. d Hydraulic lock, sample did not hydrate, data point disregarded a, 0.64 c, , 0.75, b, 10 b 0.61, 0.63, , 0.92, , 1 d 1. Samples permeated with Jet Fuel A-1 at 58C 1. Samples permeated with Jet Fuel A-1 at 58C at high flow rate. 2. Samples permeated with Jet Fuel A-1 at 58C at normal flow rate. 3. Samples permeated with Jet Fuel A-1 at 58C at normal flow rate Samples permeated with water at 58C until equilibrium 2. Samples permeated with Jet Fuel A-1 at 58C until equilibrium 3. Samples permeated with Jet Fuel A-1 at 58C until equilibrium 4. Samples permeated with Jet Fuel A-1 at 58C until equilibrium Table 4. Unfrozen sample observations for different degrees of saturation (S r ) Degree of saturation S r < 0.70 Observations Intact sidewall, but very little pressure in system, granular-looking bentonite (see Figure 2) k m/s 0.70, S r, 0.77 Bentonite was partially hydrated and partially granular S r > 0.77 Sidewall sealed to cell wall, hydrated bentonite (see Figure 3) k, 10 9 m/s Figure 2. Typical unfrozen GCL with a degree of saturation less than 70% (S r, 0.7) Figure 3. Typical unfrozen GCL with a degree of saturation greater than 77% (S r. 0.77) hydraulic gradient on hydraulic conductivity with respect to Jet Fuel A-1. Samples were permeated until equilibrium, and the hydraulic conductivity with respect to Jet Fuel A-1 was inferred. At this point, the hydraulic gradient was increased and the test repeated. In total, three separate flow rates (3 ml/s, 19 ml and 38 ml/s) and associated gradients (20 40, and 60 70, respectively) were used. For unfrozen saturated GCL samples, it

6 338 Rowe et al Hydraulic conductivity, k (m/s) Four points plotted Gravimetric water content, w c (%) Figure 4. Hydraulic conductivity of GCLs permeated with Jet Fuel A-1 against gravimetric water content at 208C Hydraulic conductivity, k (m/s) S r Bulk void ratio, e B Figure 6. Hydraulic conductivity of GCLs (permeated with Jet Fuel A-1 after initial high hydraulic gradient permeation) against bulk void ratio was observed that as hydraulic gradient increased the hydraulic conductivity with respect to Jet Fuel A-1 also increased. It is hypothesized that this trend arises from the opening of an increased number of flow paths through the GCL owing to the increase in pressure associated with the increased flow rate. Figure 5 summarizes the results for three different applied hydraulic gradients. To observe the effects of an initial high hydraulic gradient on permeation of Jet Fuel A-1, the samples were permeated again at the typical constant flow rate of 2.88 ml/day ( m 3 /m 2 /s) used for other tests. Figure 6 shows the hydraulic conductivity of GCLs permeated at high gradients until equilibrium and then permeated at a lower gradient. Upon test completion, samples were carefully removed and no evidence of hydraulic fracturing had occurred. At higher gradients, flow paths are opened and remain open, so that at lower gradients, the hydraulic conductivity does not significantly depend on bulk void ratio. To further investigate this effect, a scanning electron microscope (SEM) was used to examine the pore structure of the bentonite in GCLs. Figure 7 shows the pore structure magnified 100 times of a water-saturated sample before permeation with water or Jet Fuel A-1, and Figure 8 shows the pore structure magnified 100 times of a different water-saturated sample after permeation with Jet Fuel A-1 at a high hydraulic gradient ( 780). The flow paths created from the high gradient permeation can be seen as cracks (pointed to by arrows in the figure) in the bentonite. These cracks are relatively large, having a max width of approximately 7.6 ìm, which is about 2,500 times larger than the particle size of the bentonite (0.003 ìm for montmorillonite). The density of Jet Fuel A-1 increases as temperature decreases (hence volume decreases for a given mass), and so it is unlikely that the freezing Jet Fuel A-1 caused the cracks Hydraulic conductivity of Jet Fuel A-1 at subzero temperatures Using a constant-head apparatus in the cold room at 58C, with an air-dry sample (water content 8%) GCL thickness 8.5 mm k i ; R for 273, i, 695 GCL thickness 9.0 mm k i ; R for 381, i, Hydraulic conductivity, k (m/s) Gradient Figure 5. Hydraulic conductivity of saturated GCLs permeated with Jet Fuel A-1 against increasing gradient at 208C Figure 7. Pore structure of hydrated bentonite before permeation (initial condition, uncracked bentonite)

7 Permeating partially hydrated GCLs with jet fuel at temperatures from 208C and 208C 339 Table 5. Sample observations for different degrees of saturation at subzero temperatures Degree of saturation range Observations S r < 0.60 Leakage between cell wall and sample Bentonite had a granular texture 0.70, S r,0. 85 Sidewall sealed to cell wall Bentonite had clayey texture S r > 0.85 Essentially impermeable, k, m/s Bentonite had clayey texture Figure 8. Pore structure of hydrated bentonite after high gradient permeation with Jet Fuel A-1 showing cracks developed consolidated under 14 kpa for 24 h (with no uptake of water), but tested under zero stress, the hydraulic conductivity to Jet Fuel A-1 was found to be m/s. This represents an upper bound to hydraulic conductivity with respect to Jet Fuel A-1, and should decrease with increasing degree of saturation. Observations made following tests with different initial degrees of saturation at subzero temperatures are given in Table 5. Figure 9 and Figure 10 show the bentonite along the edge of GCLs at subzero temperatures for a degree of saturation of greater than 0.70 and less than 0.60 respectively. Figure 11 shows the variation in hydraulic conductivity of GCLs at subzero temperatures with respect to Jet Fuel A-1 as a function of bulk void ratio at two different gravimetric water contents. For a given water content, the hydraulic conductivity with respect to Jet Fuel A-1 decreases as bulk void ratio decreases. This is considered to be because, at lower bulk ratios, the flow paths are smaller, and at subzero temperatures the expanding water further decreases the size of the flow paths, resulting in a lower hydraulic conductivity with respect to Jet Fuel A-1. For the analysis of hydraulic conductivity with respect to Jet Fuel A-1 at subzero temperatures, it was assumed that most of the water in the bentonite was frozen. However, it may be anticipated that there will be small amounts of unfrozen water in the sample (e.g. water with impurities or water tightly bound to the clay particles), especially at 58C, and that this could influence the results of hydraulic conductivity with respect to Jet Fuel A Hydraulic conductivity of Jet Fuel A-1 at changing temperatures Table 6 shows the hydraulic conductivity of GCL with respect to Jet Fuel A-1 before and after freezing for a range of saturation values. In these tests, samples were sequentially permeated with Jet Fuel A-1 at 58C and 58C. For each sample there is a decrease in hydraulic conductivity at 58C. Furthermore, in general the more water in the sample prior to permeation, the larger the decrease of hydraulic conductivity with respect to Jet Fuel A-1 at 58C. The negligible flow noted from previous tests with highly saturated samples at subzero temperature conditions did not occur in these tests, and no samples had a hydraulic conductivity less than m/s. Figure 9. Edge of GCL sample with a degree of saturation greater than 0.70 after permeation with Jet Fuel A-1 at 58C Figure 10. Edge of GCL sample with a degree of saturation less than 0.60 after permeation with Jet Fuel A-1 at 58C

8 340 Rowe et al. Hydraulic conductivity, k (m/s) C 25 C Regression w c 5 60%; log k e B ; R for 1.84, e B, 2.03 w c 5 90%; log k e B ; R for 2.49, e B, 2.66 w c 5 60% w c 5 90% Bulk void ratio, e B Figure 11. Hydraulic conductivity of GCLs against bulk void ratio at subzero temperatures Table 7 summarizes the hydraulic conductivity of saturated GCLs permeated with water and Jet Fuel A-1 at 58C, Jet Fuel A-1 at 58C, and Jet Fuel A-1 at 58C. When the samples were permeated with Jet Fuel A-1 at 58C, the hydraulic conductivity increased, although the k values were still low (average k m/s). When the samples were permeated with Jet Fuel A-1 at 58C, the pressure in the cells reached the maximum permissible value quickly, indicating that there was essentially no flow and very low hydraulic conductivities. When the samples were thawed to 58C and permeated with Jet Fuel A-1, the hydraulic conductivity with respect to Jet Fuel A-1 increased approximately one order of magnitude to an average value of m/s compared with an average of m/s for water. Given the variability in the mass of bentonite between samples, one way of minimizing the effect of the variables is to present the data in terms of permittivity (i.e. hydraulic conductivity with respect to Jet Fuel A-1 divided by GCL thickness). Figures 12 and 13 show the variation in permittivity with temperature based on data collected from all tests. These calculations do not take into account fluid density or viscosity. The variation in GCL intrinsic permeability with temperature is shown in Figure 14 for three different groupings of degree of saturations. For a given degree of saturation (or water content), the intrinsic permeability decreases as temperature decreases and saturation increases. This finding is interesting, as the effects of fluid viscosity and density are both accounted for in calculation of the intrinsic permeability shown in this plot, and suggests a possible pore structure change in the unfrozen bentonite compared with frozen bentonite. It may be hypothesized that the difference is due to expanding water during freezing reducing the available flow paths available (Rowe et al. 2005). More research is required to better understand this finding. The effect of temperature on fluid density (and therefore viscosity) was obtained from the relationship defined by Lewis and Squires (1934). 5. DISCUSSION The hydraulic conductivity of the tested GCL with respect to Jet Fuel A-1 decreased as the degree of saturation increased and as temperature decreased. The data obtained at a confining pressure of 14 kpa suggests that for GCLs to perform well as an advective barrier against Jet Fuel A-1 they should be saturated to a degree of saturation of Table 6. Hydraulic conductivity of unsaturated GCLs permeated with Jet Fuel A-1 before and after freezing Degree of saturation, S r Gravimetric water content, w c (%) Hydraulic conductivity, k, at +58C (m/s) Hydraulic conductivity, k, at 58C (m/s) % decrease of hydraulic conductivity, k Table 7. Hydraulic conductivity of saturated GCLs permeated with Jet Fuel A-1 before and after freezing Mass of bentonite (kg/m 2 ) Hydraulic conductivity with water at 58C (m/s) Hydraulic conductivity, k, with Jet Fuel A-1 at 58C (m/s) Hydraulic conductivity, k, with Jet Fuel A-1 at 58C (m/s) Hydraulic conductivity, k, with Jet Fuel A-1 at 58C after one freeze (m/s) , , , , , , , Data acquisition error ,

9 Permeating partially hydrated GCLs with jet fuel at temperatures from 208C and 208C Regression 0.60, S r, 0.70: log ø T ; R for 220, T, , S r, 0.85: log ø T ; R for 220, T, 20 S r. 0.85: log ø T ; R for 25, T, Regression 0.60, S r, 0.70: log k T ; R for 220, T, , S r, 0.85: log k T ; R for 220, T, 20 S r. 0.85: log k T ; R for 25, T, 20 Permittivity, ø (1/s) Intrinsic permeability, k (m 2 ) Temperature, T ( C) Temperature, T ( C) Figure 12. Change in permittivity of GCL permeated with Jet Fuel A-1 with temperature for three ranges of degree of saturation Figure 14. Variation in intrinsic permeability of GCL permeated with Jet Fuel A-1 with temperature for three ranges of degree of saturation Permittivity, ø (1/s) Regression w c 5 060%: log ø T ; R for 220, T, 20 w c 5 090%: log ø T ; R for 220, T, 20 w c 5 120%: log ø T ; R for 25, T, Temperature, T ( C) Figure 13. Change in permittivity of GCL permeated with Jet Fuel A-1 with temperature at three gravimetric water contents greater than 0.77 for unfrozen conditions and 0.70 for subzero temperatures. In terms of water contents, the data suggest that, for subzero temperatures, GCLs with water contents greater than 60% should achieve a hydraulic conductivity of k < m/s with respect to Jet Fuel A-1. For unfrozen conditions, GCLs with water contents greater than 90% should achieve a hydraulic conductivity with respect to Jet Fuel A-1 of approximately 10 9 m/s (or less). Tables 8 and 9 summarize the hydraulic conductivities deduced from the testing completed at temperatures between 20 and +208C. Daniel et al. (1993) buried GCLs in sand with different water contents and measured the rate of wetting of the bentonite. They reported that for GCLs on sand with initial gravimetric water contents higher than 5%, the water content of the bentonite in the GCL reached approximately 100% (or higher) in the first 5 days, and % after 45 days. For sand with an initial water content of 2 3%, the water content in the bentonite of the GCL reached approximately 35 40% after 5 days and approximately 80% after 45 days. The GCLs approached their equilibrium water content in 1 3 weeks. Table 10 summarizes the findings of Daniel et al. (1993). The results of Daniel et al. (1993) combined with the results presented herein suggest that in practical situations where the GCL is placed on damp to moist soil the hydration that would occur over a few weeks would be sufficient for the GCL to have a hydraulic conductivity with respect to Jet Fuel A-1 of less than m/s at temperatures between 20 and +208C, as long as the GCL does not dry out. In a cold and dry winter it is feasible Table 8. Hydraulic conductivity of unfrozen GCLs permeated with Jet Fuel A-1 Degree of saturation Gravimetric water content, w c (%) Hydraulic conductivity, k (m/s) S r S r < S r > < S r a (SD b m/s) a Mean of 8 samples. b Standard deviation.

10 342 Rowe et al. Table 9. Hydraulic conductivity of GCLs permeated with Jet Fuel A-1 at subzero temperatures Degree of saturation Gravimetric water content, w c (%) Hydraulic conductivity (m/s) S r 0 8% (constant-head apparatus) S r < % Samples experienced sidewall leakage 0.70, S r, % to S r > 0.85 > 110% < Table 10. Approximate water contents of GCLs depending on subgrade (modified from Daniel et al. 1993) Subgrade soil Approximate water content, w c,of bentonite (%) Extremely dry soil, does not support plant growth (soil suction kpa), 50 Damp soil, supports sparse growth of plants (100 kpa < soil suction < 1500 kpa) Moist soil, supports lush vegetation (0 kpa < soil suction < 100 kpa) Wet soil (practically saturated), soil suction (0 kpa). 140 that a GCL could dry out, affecting the hydraulic performance; however, in subzero conditions most of the water in the GCL should be frozen, which would help mitigate this. Thus it would be important to ensure adequate hydration prior to subzero temperatures to help avoid this situation. As always, engineering judgment is required in assessing the appropriateness of information such as presented herein to the design of barriers involving geosynthetics (including GCLs). 6. CONCLUSIONS A constant-flow fixed-wall apparatus was used to examine the hydraulic conductivity of GCLs with respect to Jet Fuel A-1 for saturated and unsaturated conditions and a range of temperatures. For the GCLs and conditions examined it is concluded that: The hydraulic conductivity with respect to Jet Fuel A-1 of unfrozen samples decreased as the water content increased. Higher water contents corresponded to more swelling, and consequently the decrease in hydraulic conductivity with respect to Jet Fuel A-1 also corresponded to an increasing bulk void ratio that accompanies higher swelling at a given (in this case 14 kpa) stress level. If samples are first permeated with Jet Fuel A-1 at 58C and then Jet Fuel A-1 at 58C, the hydraulic conductivity with respect to Jet Fuel A-1 drops, but some of the flow paths remain open. In general, the higher the degree of saturation, the greater the decrease in hydraulic conductivity with respect to Jet Fuel A-1 at 58C. Hydraulic conductivity with respect to Jet Fuel A-1 depends on the applied hydraulic gradient for saturated unfrozen samples. It is hypothesized that higher pressures open up more flow paths than were previously available, thereby increasing the hydraulic conductivity with respect to Jet Fuel A-1. The hydraulic conductivity with respect to Jet Fuel A-1 of samples at subzero temperatures permeated with Jet Fuel A-1 decreased as the bulk void ratio decreased for a given water content. It is hypothesized that, as the bulk void ratio decreases, the size of the flow paths available decreases, and consequently, as the freezing water expands, it constricts the flows paths and results in a large decrease in hydraulic conductivity with respect to Jet Fuel A-1. There is a high variability in the hydraulic properties for samples at subzero temperatures due to different mass per unit area of bentonite and localization of ice masses. ACKNOWLEDGMENTS The research reported in this paper was funded by CRESTech, a division of Ontario Centres of Excellence Inc., Terrafix Geosynthetics Inc and NAUE GmbH & Co. KG. NOTATIONS Basic SI units are given in parentheses: e B bulk void ratio (dimensionless) i hydraulic gradient (dimensionless) k hydraulic conductivity (m/s) K intrinsic permeability (m 2 ) S r degree of saturation (dimensionless) T temperature (8C) w c gravimetric water content (dimensionless) í kinematic viscosity (m 2 /s) Ø permittivity (1/s)

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