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문제 정의
- The tests are conducted until complete chemical equilibrium between the influent and effluent is established, which in some cases required in excess of 2 yrs of permeation. The results of this study should improve our understanding of appropriate termination criteria to be used for compatibility testing of GCLs.
제안 방법
- Specimens of the two GCLs with nominal diameters of 102 mm were permeated using the falling-head procedure and flexible-wall permeameters in accordance with ASTM D 5084. Hydraulic conductivity tests were performed on both non-prehydrated and prehydrated specimens of the GCL with the lower bentonite quality (i.e., GCL-LQB), as well as non-prehydrated specimens for the GCL with the higher bentonite quality (i.e., GCL-HQB). Prehydration was achieved by permeating the GCL specimens with DIW.
- Hydraulic conductivity tests were performed on two geosynthetic clay liners (GCLs) containing different qualities of bentonite with or without prehydration to evaluate adequacy of a wide range of termination criteria commonly used in compatibility testing of GCLs with respect to prehydration and quality of bentonite by permeating the GCL specimens with calcium chloride (CaCh) solutions. All of the hydraulic conductivity tests are not terminated before chemical equilibrium between hydraulic conductivity has been established.
- To determine equilibrium in hydraulic conductivity, the slope of hydraulic conductivity versus number of PVF was analyzed statistically using linear regression based on the t-test at a 5% significance level as described in Peirce and Witter (1986). The statistically zero slope of hydraulic conductivity was evaluated through analyzing the slope of five successive hydraulic conductivity values in series.
- The test results based on the physical termination criteria, including volumetric flow ratio and steady hydraulic conductivity per ASTM D 5084, 2 pore volumes of flow (PVF), and constant thickness of specimen as the hydraulic conductivity ratios based on 2 PVF (i.e.s k2PVF/k/k o) are between 0.1 and 0.5 except for one test performed with the 10 mM CaCh solution. In addition, the hydraulic conductivity values based on the constant thickness of specimens (kn) are from 2X to 5X lower than the kjk~o values.
대상 데이터
- 2 mS/m) and solutions containing concentrations of calcium chloride (CaCh) ranging from 5 mM to 100 mM. The processed tap water is classified as Type IV deionized water (DIW) as per ASTM D 1193. Calcium chloride was chosen primarily because previous studies involving permeation of bentonite-based hydraulic barrier materials (e.
- Two geosynthetic clay liners (GCLs) containing bentonite with different montmorillonite contents were used in this study. Both GCLs consist of a thin layer of granular sodium bentonite sandwiched between two polypropylene geotextiles held together by needle-punched fibers.
데이터처리
- 3 yr) of permeation depending on prehydration condition and quality of bentonite in the GCLs, and then appear to stabilize. To determine equilibrium in hydraulic conductivity, the slope of hydraulic conductivity versus number of PVF was analyzed statistically using linear regression based on the t-test at a 5% significance level as described in Peirce and Witter (1986). The statistically zero slope of hydraulic conductivity was evaluated through analyzing the slope of five successive hydraulic conductivity values in series.
이론/모형
- Particle-size distributions of the bentonite portions of the two GCLs were determined using both mechanical sieve analysis of the air-dried bentonite and hydrometer analysis (ASTM D 421, D 422). For both GCLs, the air-dried bentonite consists of more than 90% by dry weight (w/w) sand-sized granules (75 to 2000 mm) based on the mechanical sieve analyses, whereas approximately 90 % of particles are clay sized (< 5 # m) based on the hydrometer analyses.
- Prehydration was achieved by permeating the GCL specimens with DIW. The specimens were trimmed and assembled in the permeameters using the method described by Daniel et al. (1997) to prevent the possibility of short circuiting through the geotextiles at the edge of the GCL specimens due to loss of bentonite and pinching of the geotextiles. Backpressure was not used so that effluent liquids could be conveniently collected for measuring pH, EC, and solute concentration.
성능/효과
- For both GCLs, the air-dried bentonite consists of more than 90% by dry weight (w/w) sand-sized granules (75 to 2000 mm) based on the mechanical sieve analyses, whereas approximately 90 % of particles are clay sized (< 5 # m) based on the hydrometer analyses. Consequently, the bentonites from both GCLs are classified as high plasticity clays (CH) according to the Unified Soil Classification System (ASTM D 2487) based on the wet analyses, whereas the results from the mechanical analyses indicate that the air-dried bentonites actually consist of assemblages or granules (i.e., clods) of individual clay particles and, therefore, are classified as poorly graded sand (SP). Shackelford et al.
- In other words, significantly more PVF (10 to 73 more) are required to achieve k/k~o than are required to meet the physical termination criteria. In fact, the overall physical termination criteria required 3 PVF, representing 40 days of permeation, for both non-prehydrated and prehydrated specimens of GCL-LQB permeated with 5, 10, and 20 mM CaCh solutions, whereas > 18 PVF for the non- prehydrated specimens and a minimum of 10 PVF for the prehydrated specimens are required to achieve the kjk-o- For the specimens permeated with 50 and 100 mM CaCh solutions, the elapsed time and PVF required to achieve each criterion as well as kjk~o generally are greater for the prehydrated specimens than for the non-prehydrated specimens.
후속연구
- As a result of the aforementioned considerations, the objective of this study is to evaluate the potential dependency of criteria commonly used to terminate laboratory compatibility tests on the prehydration and the quality of bentonite for GCLs permeated with CaCh solutions. In order to achieve this objective, hydraulic conductivity tests are performed on both non-prehydrated and prehydrated specimens of a single GCL containing relatively low quality bentonite as well as non-prehydrated specimens of a different GCL containing relatively high quality bentonite.
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