Consolidation of a Geosynthetic Clay Liner under Isotropic States of Stress

Transcription

1 Consolidation of a Geosynthetic Clay Liner under Isotropic States of Stress Jong-Beom Kang, Ph.D. 1 ; and Charles D. Shackelford, Ph.D. 2 Abstract: The consolidation behaior of a geosynthetic clay liner GCL was ealuated by consolidating duplicate specimens of the GCL in a flexible-wall cell to a final effectie stress,, of 241 kpa 35.0 psi. The hydraulic conductiity, k, also was at the end of each loading increment. The results indicated that the GCL was normally consolidated for alues of greater than 34.5 kpa 5.0 psi, which correlates well with limited consolidation data reported in the literature for GCLs based on confined compression using oedometers. Values of the coefficient of consolidation, c, for the GCL ranged from m 2 /s to m 2 /s, and generally decreased with increasing, albeit only slightly. Values of the k, k, for the GCL were low cm/s due to the sodium bentonite content of the GCL, and were within a factor of about two of the alues of k calculated on the basis of classic Terzaghi small-strain consolidation theory, k theory i.e., 0.5 k theory /k 2.0, suggesting that the theory is appropriate for describing the consolidation behaior of the GCL. The results also are consistent with the results of preious studies based on one-dimensional consolidation of sodium montmorillonite, suggesting that there would be little difference in the consolidation behaior of the GCL under confined compression. DOI: 161/ ASCE GT CE Database subject headings: Soil compression; Soil consolidation; Geosynthetics; Clay liners; Hydraulic conductiity. Author keywords: Compressibility; Consolidation; Geosynthetic clay liner; Hydraulic conductiity. Introduction Extensie research has been performed on both the hydraulic performance of geosynthetic clay liners GCLs to a ariety of permeant liquids e.g., Daniel et al. 1997; Shackelford et al. 2000; Rowe 2005; Shackelford 2007 and the shear strength of GCLs e.g., Fox and Stark In contrast, ery little research has been performed on the consolidation behaior of GCLs. In fact, the only study of which the writers are aware that contains consolidation results for GCLs is the dissertation by Shan Howeer, Shan 1993 did not report alues of the compression index, C c, or the coefficient of consolidation, c, because the primary purpose of the testing was to determine the times to achiee 50% consolidation for use in determining the displacement rates to be used in shear strength testing of the GCLs. Shan 1993 also performed only one-dimensional consolidation testing in oedometers. In contrast, the approach in this study was on assessing the consolidation behaior of a GCL contained within a flexible-wall cell and subjected to isotropic states of stress. 1 Geotechnical Engineer, Engineering Analytics, Inc., 1600 Specht Point Rd., Suite 209, Fort Collins, CO 80525; formerly, Graduate Research Assistant, Dept. of Ciil and Enironmental Engineering, Colorado State Uni. jkang@enganalytics.com 2 Professor, Dept. of Ciil and Enironmental Engineering, Colorado State Uni., 1372 Campus Deliery, Fort Collins, CO corresponding author. shackel@engr.colostate.edu Note. This manuscript was submitted on August 18, 2008; approed on June 17, 2009; published online on June 20, Discussion period open until June 1, 2010; separate discussions must be submitted for indiidual papers. This technical note is part of the Journal of Geotechnical and Geoenironmental Engineering, Vol. 136, No. 1, January 1, ASCE, ISSN /2010/ /$ Materials and Experimental Methods Materials The GCL ealuated in this study is the same as that tested by Malusis and Shackelford 2002 for semipermeable membrane behaior. The bentonite component of the GCL contained 71% smectite montmorillonite, 7% mixed layer illite/smectite, 15% quartz, and 7% other minerals. The liquid limit and plastic limit ASTM D4318 were reported as 478 and 39%, respectiely, and the bentonite classified as high plasticity clay CH based on the unified soil classification system ASTM D2487. Further details regarding the physical and chemical properties of the GCL bentonite are proided by Malusis and Shackelford Specimen Assembly and Preparation Duplicate specimens of the GCL i.e., and were consolidated in this study in preparation for testing for membrane behaior, the results of which are reported in Kang and Shackelford The specimen preparation consisted of two stages: 1 a flushing stage and 2 a consolidation and permeation stage. The purpose of the flushing stage was to leach soluble salts from the GCL bentonite to enhance the potential for membrane behaior see Kang and Shackelford The purposes of the consolidation and permeation stage were to consolidate the specimens to a sufficiently high effectie stress to again enhance the potential for membrane behaior, and to measure the hydraulic conductiity, k, of the specimens for comparison with the alue of k based on classic small-strain Terzaghi consolidation theory. For the flushing stage, circular specimens of the GCL with JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ASCE / JANUARY 2010 / 253

2 nominal diameters of 102 mm were permeated in standard flexible-wall permeameters e.g., Daniel et al. 1985; Daniel 1994 at an rage effectie stress of 34.5 kpa 5.0 psi with deionized water DIW. After completion of the flushing stage, the GCL specimens were transferred to separate but identical flexible-wall cells for the purpose of consolidating the specimens under isotropic loading conditions. After reassembling the specimens in the flexible-wall cells, the specimens were initially consolidated back to an rage effectie stress of 34.5 kpa 5.0 psi. Thereafter, the specimens were subsequently consolidated in three 69.0 kpa 10.0 psi increments until the desired final effectie stress of 241 kpa 35.0 psi had been achieed. Volume changes V were monitored ersus time ia measuring changes in the air-water interface within the cell-water accumulator attached to the flexible-wall cell, and changes in the specimen height H were determined using a telescope sighted to markings located on the specimen membrane located within the flexible-wall cell e.g., see Daniel et al. 1985; Daniel Values for k were at the end of each incremental loading stage in general accordance with procedures in ASTM D5084 using the falling headwater and rising tailwater procedure. Howeer, DIW was used as the permeant liquid instead of the standard water specified in ASTM D5084, and the rage hydraulic gradient of 330 was greater than the maximum gradient i.e., 30 stipulated in ASTM D5084 for soils with low hydraulic conductiity k 10 7 cm/s. Hydraulic gradients ranging from 50 to 600 typically are used for measuring the k of GCLs due to the typically low k of GCLs, and the k of GCLs has been shown to be affected to a greater extent by rage effectie stress than by the magnitude of hydraulic gradient Shackelford et al Further details on these procedures are proided in Kang Results and Discussion Strain ersus Time Plots of ical strain and umetric strain ersus both logarithm of time log t and square root of time t 1/2 for each consolidation stage are shown for both specimens in Fig. 1. As indicated in Fig. 1, alues of were slightly lower than alues of at a gien time, which is consistent with smaller differences between ical deformations, H, ersus umetric deformations, V, relatie to the greater differences between initial specimen height, H o, ersus initial specimen ume, V o i.e., 8.23 mm H o 8.86 mm ersus 71,207 mm 3 V o 75,170 mm 3. In general, the umetric deformations were considered to be more reliable than the ical deformations, primarily because measurements of V based on changes in the water leel in the cell-water accumulator of the flexible-wall cell were easier and likely more accurate than were measurements of H using a telescope, due to the relatie difficulty in sighting the reference mark on the specimen membrane within the flexible-wall cell with the telescope. Stress ersus Strain Stress-ersus-strain stress-strain cures in the form of,, and oid ratio e ersus logarithm of for both GCL specimens are shown in Fig. 2. The stress-strain cure presented in terms of oid ratio Fig. 2 b is based only on umetric strains i.e., not ical strains, because the specimens were not confined to only ical deformation, although drainage was only ical and the relatiely close agreement between and suggests that any lateral deformation was relatiely minor i.e., ical deformation was predominant. Also, no distinction was made between the geotextile and bentonite portions of the GCL, such that all oid ratios represent the bulk oid ratios of the GCL. Seeral obserations are readily apparent from the stress-strain cures shown in Fig. 2. First, the stress-strain cures are all semilog linear, such that no stress history is eident and the GCL specimens were normally consolidated. This obseration is consistent with the fact that the maximum preious effectie stress, max, of 34.5 kpa 5.0 psi was applied during the flushing stage of the specimen preparation, such that effectie stresses greater than 34.5 kpa 5.0 psi should h resulted in irgin compression of the specimens. Second, the alues of the compression ratio, = / log, and compression index, C c = e/ log, for both GCL specimens are reasonably close, with the and C c alues for specimen being slightly lower than those for specimen. For example, the ratios of for specimen to for specimen are 1.24 =0.297/0.239 based on and 1.22 =0.278/0.228 based on, whereas the ratio of C c for specimen to C c for specimen is These differences in and C c alues between the two specimens reflect, in part, the likely inherent ariability associated with the GCL specimens e.g., slightly different bentonite contents. Third, alues for based on tend to be slightly greater than those based on for both GCL specimens. This difference in is consistent with being slightly greater than as preiously noted. Coefficients of Consolidation Values for the coefficient of consolidation, c, based on the timestrain plots in Fig. 1 are summarized in Table 1. As indicated in Table 1, the alue of c at a gien for specimen tended to be greater than that for specimen. For example, the ratio of the alues of c for specimen relatie to those for specimen range from 1.1 to 1.9. Also, the ratio of the alues of c for specimen relatie to those for specimen tended to be the greatest at a final alue for of 241 kpa 35.0 psi relatie to of 103 kpa 15.0 psi or 172 kpa 25.0 psi. The alues of c based on umetric strains are plotted as a function of the rage consolidation effectie stress,, for the loading increment in Fig. 3 a. Note that is used instead of the final because alues of c calculated in accordance with the Casagrande method are based on the time to achiee 50% consolidation of the applied loading increment, t 50, such that only half of the applied loading increment has been transferred to effectie stress at t 50. As shown in Fig. 3 a, c for a gien GCL specimen decreases with increasing, albeit only slightly. This trend is consistent with that obsered by Robinson and Allam 1998 for sodium montmorillonite consolidated one dimensionally under confined compression, and can be attributed to the dominance of physicochemical factors in controlling c ersus mechanical factors as described by Olson and Mesri In addition, the range in c alues obtained in this study is similar to, albeit somewhat greater than, the range in c alues of m 2 /s c m 2 /s obtained by Robinson and Allam This relatiely good agreement in c alues 254 / JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ASCE / JANUARY 2010

3 Vertical Strain, ε or Volumetric Strain, ε σ' =103kPa(15.0psi (ε (ε (ε (ε (a Vertical Strain, ε or Volumetric Strain, ε σ' = 103 kpa (15.0 psi (b (ε (ε (ε (ε ,000 10,000 Time, t (min Time, t 1/2 (min Vertical Strain, ε (- H/H or o Volumetric Strain, ε (- V/V o σ' =172kPa(25.0psi (ε (ε (ε (ε (c Vertical Strain, ε or Volumetric Strain, ε σ' = 172 kpa (25.0 psi (d (ε (ε (ε (ε ,000 10,000 Time, t (min Time, t 1/2 (min Vertical Strain, ε r o Volumetric Strain, ε (- V/V o σ' = 241 kpa (35.0 psi (ε (ε (ε (ε (e Vertical Strain, ε r o Volumetric Strain, ε (- V/V o σ' = 241 kpa (35.0 psi (f (ε (ε (ε (ε ,000 10,000 Time, t (min Time, t 1/2 (min Fig. 1. Strain ersus time for isotropic consolidation for two specimens of a GCL; a, c, and e logarithm of time; b, d, and f square root of time between the two studies suggests that there would be little difference in the consolidation behaior of the GCL under confined compression. The alues of c based on ical strains,, relatie to those based on are plotted as a function of in Fig. 3 b. In all cases, the alues of c based on are lower than those based on 0.54 c based on /c based on 0.93, although the difference is relatiely minor 0.89 c based on /c based on 0.93 in the case of specimen based on the Taylor method of analysis. Also, as shown in Fig. 3 c, alues of c based on the Taylor method relatie to those based on the Casagrande method, or c,taylor /c,casagrande, are practically the same for both GCL specimens regardless of the alue of or whether the c alues were based on either or. Thus, the method of analysis had a relatiely minor effect on the determination of c for the GCL and test conditions ealuated in this study. This conclusion is in contrast to that based on consolidation of natural clays, where c based on the Taylor method typically is greater than c based on the Casagrande method Olson Hydraulic Conductiity The alues of the hydraulic conductiity at the end of each loading increment, k, are summarized in Table 1 and shown ersus the oid ratio, e, for each GCL specimen in Fig. 4. The alues of k reported in Table 1 are in good agreement with other alues of k for GCLs based on permeation with water, which typically are on the order of cm/s Daniel et al The resulting semilog linear trends in k ersus e shown in Fig. 4 are consistent with similar trends preiously reported for both bentonite e.g., Mesri and Olson 1971 and GCLs e.g., Shackelford et al JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ASCE / JANUARY 2010 / 255

4 Vertical Strain, ε or Volumetric Strain, ε Void Ratio, e = (r 2 = (ε (ε (ε (ε = (r 2 = Effectie Stress, σ' (kpa C c =1.57 (r 2 = Values of hydraulic conductiity based on consolidation theory, k theory, were calculated in accordance with the following expression: k theory = c m w g = c a w g 1 1+e o where m and a = alues of the coefficient of ume compressibility and the coefficient of compressibility, respectiely; e o =initial oid ratio; w =density of water; and g=acceleration due to graity. The alues of m and a used in Eq. 1 to determine k theory are shown in Fig. 5 as a function of, and are in general agreement with the range of alues for m of kpa 1 m kpa 1 reported by Robinson (a = (r 2 = =0.278 (r 2 = C c =1.31 (r 2 = Effectie Sress, σ' (kpa Fig. 2. Compression parameters for two specimens of a GCL: a compression ratios; b compression indices (b Coefficient of Consolidation, c (m 2 /s c based on ε / c based on ε c,taylor / c,casagrande Aerage Effectie Stress, σ' (psi (Casagrande (Taylor (Casagrande (Taylor Aerage Effectie Stress, σ' (kpa and Allam 1998 based on one-dimensional consolidation of sodium montmorillonite for the same range in effectie stress. The resulting alues of k theory calculated in accordance with Eq. 1 using alues of c based on the Casagrande method are plotted as a function of in Fig. 6 a and compared with the alues of k, k, in Fig. 6 b. As shown in Fig. 6 a, k theory decreases with increasing, which is consistent with the trends in both c and m or a with Figs. 3 a and 5. In addition, the range in k theory alues obtained in this study is almost identical to the range of alues for k theory of cm/s k theory cm/s reported by Robinson and Allam 1998 based on one-dimensional consolidation of sodium montmorillonite for the same range in effectie stress. (a Aerage Effectie Stress, σ' (psi 1.0 (b Casagrande- 0.4 Taylor- 0.2 Casagrande- Taylor- 0.0 Aerage Effectie Stress, σ' (kpa AerageEffectieStress, σ' (psi (from ε (c 6 (from ε (from ε (from ε 1 0 Aerage Effectie Stress, σ' (kpa Fig. 3. Coefficients of consolidation, c, for two specimens of a GCL ersus rage effectie stress: a c based on umetric strain ; b effect of type of strain; and c effect of method of analysis Table 1. Values of the Measured Hydraulic Conductiity and Coefficient of Consolidation for Two Specimens of a GCL Effectie stress a kpa psi Measured hydraulic conductiity k 10 9 cm/s Casagrande method Coefficient of consolidation, c 10 9 m 2 /s Taylor method Vertical strain Volumetric strain Vertical strain Volumetric strain a Final effectie stress at the end of consolidation and rage effectie stress during permeation. 256 / JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ASCE / JANUARY 2010

5 Measured Hydraulic Conductiity, k (cm/s 10-7 log k (cm/s = e (r 2 =0.970 log k (cm/s = e (r 2 = Void Ratio, e Measured Hydraulic Conductiity, k (m/s Fig. 4. Measured hydraulic conductiity ersus oid ratio for two specimens of a GCL permeated with DIW at the end of each loading stage Finally, as shown in Fig. 6 b, there is relatiely good agreement between k theory and k, regardless of the type of strain ersus used to calculate k theory. For example, k theory /k aries by only about a factor of two i.e., 0.5 k theory /k 2.0 for both GCL specimens. The same obserations and conclusions result when alues of k theory calculated in accordance with Eq. 1 using alues of c based on the Taylor method are considered. The relatiely good agreement between k theory and k suggests that classic small-strain Terzaghi consolidation theory is appropriate for describing the consolidation behaior of the GCL e.g., Olson Coefficient of Volume Compressibility, m (kpa -1 Coefficient of Compressibility, a (kpa Aerage Effectie Stress, σ' (psi (from ε (from ε (from ε (from ε (a Aerage Effectie Stress, σ' (kpa Aerage Effectie Stress, σ' (psi (from ε (from ε (from ε (from ε Aerage Effectie Stress, σ' (kpa Fig. 5. Compressibility based on ical strain and umetric strain for two specimens of a GCL as function of rage effectie stress: a coefficient of ume compressibility; b coefficient of compressibility (b 10-1 Compressibility, m (psi -1 Coefficient of Compressibility, a (psi -1 Coefficient of Volume Theoretical Hydraulic Conductiity, k (cm/s theory Secondary Compression Values of the secondary compression ratio, R, and the secondary compression index, C, based on both and are summarized in Table 2 and plotted ersus final in Figs. 7 a and b, respectiely, where R and C are defined as follows: and Theoretical Hydraulic Conductiity, k theory (cm/s Aerage Effectie Stress, σ' (psi (from ε (from ε (from ε (from ε Aerage Effectie Stress, σ' (kpa R, = log t ;R, = log t C, = e log t = R, 1+e o ;C, = e log t = R, 1+e o where e and e =changes in oid ratios corresponding to the changes in and, respectiely. The alues of R and C for specimen at a gien are always slightly greater than the corresponding alues for specimen. In addition, the alues of R and C for both GCL specimens decrease essentially linearly with increasing. Finally, as shown in Fig. 7 c, alues of R, /R, =C, /C, also tended to decrease approximately linearly as increases from 103 kpa 15.0 psi to 241 kpa 35.0 psi, although the correlation for specimen is not as good as that for specimen. (a Measured Hydraulic Conductiity, k (m/s k theory /k =2.0 (b (from ε (from ε (from ε (from ε Measured Hydraulic Conductiity, k (cm/s Theoretical Hydraulic Conductiity, k theory (m/s Theoretical Hydraulic Conductiity, k (m/s theory Fig. 6. Theoretical hydraulic conductiity, k theory, calculated using c by Casagrande method and m from ical strain or umetric strain for two specimens of a GCL: a k theory ersus rage effectie stress; b comparison of theoretical ersus hydraulic conductiity JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ASCE / JANUARY 2010 / 257

6 Table 2. Values of the Secondary Compression Ratio R and Secondary Compression Index C for Two Specimens of a GCL R 10 2 C 10 2 Effectie stress Vertical strain, R, Volumetric strain, R, Vertical strain, C, Volumetric strain, C, kpa psi Conclusions The stress-ersus-strain cures for duplicate specimens of the GCL ealuated in this study were semilog linear, such that the GCL specimens were normally consolidated for alues of greater than 34.5 kpa 5.0 psi. This obseration is consistent with limited published results based on confined compression using Secondary Compression Ratio with Respect to Vertical Strain, R, α, Secondary Compression Index with Respect to Vertical Strains, C, α, Ratio of Secondary Compression Ratios, R /R (= C /C α, α, α, α, or Volumetric Strain, R α, or Volumetric Strain, C α, Effectie Stress, σ' (psi R = x σ' (kpa (r 2 =0.978 α, (a R = x σ' (kpa α, 0.01 (r 2 =0.987 R α, = x σ' (kpa (r 2 =0.987 R = x σ' (kpa (r 2 =0.997 α, Effectie Stress, σ' (kpa Effectie Stress, σ' (psi C = x σ' (kpa (r 2 =0.978 α, (b C = x σ' (kpa α, 0.05 (r 2 = C α, = x σ' (kpa, (r 2 =0.987 C = x σ' (kpa (r 2 =0.997 α, Effectie Stress, σ' (kpa Effectie Stress, σ' (psi R /R = x σ' (kpa (c α, α, 1 (r 2 =0.907 R α, /R α, = x σ' (kpa (r 2 = Effectie Stress, σ' (kpa Fig. 7. Secondary compression based on ical strain and umetric strain for two specimens of a GCL ersus effectie stress: a secondary compression ratio; b secondary compression index; and c ratio of secondary compression ratios conentional oedometers of four different GCLs indicating alues for max of 38.3 kpa 5.6 psi for all four GCLs and 34.5 kpa 5.0 psi for three of the four GCLs. The coefficients of consolidation, c, for the two GCL specimens ranged from m 2 /s to m 2 /s, and are consistent with preiously published results based on onedimensional consolidation of sodium montmorillonite for the same range in effectie stress. This consistency in c alues suggests that there would be little difference in the consolidation behaior of the GCL under confined compression. In addition, c for a gien GCL specimen decreased with increasing, albeit only slightly. This trend in c also is consistent with preiously published results based on one-dimensional consolidation of sodium montmorillonite, and has been attributed to the dominance of physicochemical factors relatie to mechanical factors in goerning consolidation behaior of clays. Values of the hydraulic conductiity at the end of each loading increment, k, as well as those calculated on the basis of consolidation theory, k theory, generally were found to decrease with increasing, which is consistent with decreases in oid ratio with increasing. In addition, the range of alues for k was similar to that for k theory i.e., cm/s k cm/s ersus cm/s k theory cm/s, which suggests that classic small-strain Terzaghi consolidation theory is appropriate for describing the consolidation behaior of the GCL. The alues of the compression ratio,, and compression index, C c, for both GCL specimens were reasonably close. Also, the ratio of for specimen to for specimen based on was essentially the same as that based on, indicating little influence in terms of the type of strain used in the analysis. Values of the secondary compression ratio, R, based on both R, and R,, and the associated secondary compression index, C, were found to decrease essentially linearly as increased from 103 kpa 15.0 psi to 241 kpa 35.0 psi. Values of R, /R, =C, /C, also tended to decrease approximately linearly with increasing. Acknowledgments Financial support for this study was proided by the U.S. National Science Foundation NSF, Arlington, VA, under Grant Nos. CMS entitled, Membrane Behaior of Clay Soil Barrier Materials and CMS entitled, Enhanced Clay Membrane Barriers for Sustainable Waste Containment. The opinions expressed in this paper are solely those of the writers and are not necessarily consistent with the policies or opinions of the NSF. 258 / JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ASCE / JANUARY 2010

7 References Daniel, D. E State-of-the-art: Laboratory hydraulic conductiity test for saturated soils. Hydraulic conductiity and waste contaminant transport in soil, ASTM STP1142, D. E. Daniel and S. J. Trautwein, eds., ASTM, West Conshohocken, Pa., Daniel, D. E., Anderson, D. C., and Boynton, S. S Fixed-wall ersus flexible-wall permeameters. Hydraulic barriers in soil and rock, ASTM STP874, A. I. Johnson, R. K. Frobel, N. J. Caalli, and C. B. Pettersson, eds., ASTM, West Conshohocken, Pa., Daniel, D. E., Bowders, J. J., and Gilbert, R. B Laboratory hydraulic conductiity testing of GCLs in flexible-wall permeameters. Testing and acceptance criteria for geosynthetic clay liners, ASTM STP1308, L. Well, ed., ASTM, West Conshohocken, Pa., Fox, P. J., and Stark, T. D State-of-the-art: GCL shear strength and its measurement. Geosynthet. Int., 11 3, Kang, J.-B Membrane behaior of clay liner materials. Ph.D. dissertation, Colorado State Uni., Fort Collins, Colo. Kang, J.-B., and Shackelford, C. D Clay membrane testing using a flexible-wall cell under closed-system boundary conditions. Appl. Clay Sci., , Malusis, M. A., and Shackelford, C. D Chemico-osmotic efficiency of a geosynthetic clay liner. J. Geotech. Geoeniron. Eng., 128 2, Mesri, G., and Olson, R. E Mechanisms controlling the permeability of clays. Clays Clay Miner., 19 3, Olson, R. E State of the art: Consolidation testing. Consolidation of soils, testing and ealuation, ASTM STP892, R.N.YongandF. C. Townsend, eds., ASTM, West Conshohocken, Pa., Olson, R. E., and Mesri, G Mechanisms controlling the compressibility of clays. J. Soil Mech. and Found. Di., 96 SM6, Robinson, R. G., and Allam, M. A Effect of clay mineralogy on coefficient of consolidation. Clays Clay Miner., 46 5, Rowe, R. K Long-term performance of contaminant barrier systems. Geotechnique, 55 9, Shackelford, C. D Selected issues affecting the use and performance of GCLs in waste containment applications. Proc., 21st Geotechnical Engineering Conf., M. Manassero and A. Dominijanni, eds., Politecnico di Torino, Torino, Italy, Shackelford, C. D., Benson, C. H., Katsumi, T., Edil, T. B., and Lin, L Ealuating the hydraulic conductiity of GCLs permeated with non-standard liquids. Geotext. Geomembr., , Shan, H.-Y Stability of final coers placed on slopes containing geosynthetic clay liners. Ph.D. dissertation, Uni. of Texas, Austin, Tex. JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ASCE / JANUARY 2010 / 259