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The relative improvement of the diffusive barrier function of high density polyethylene (HDPE) geomembranes to volatile organic compounds (VOCs) when subjected to surface fluorination is experimentally examined. The surface fluorination consisted of applying elemental fluorine, which exchanged with hydrogen along polymer chains at the surface of a polyolefin substrate. Sorption and diffusion tests were performed on both traditional 'untreated' and 'fluorinated' 1.5 mm HDPE geomembranes using dilute aqueous organic contaminants commonly found in municipal solid waste leachate. The partitioning coefficient is shown to remain essential the same after the surface fluorination; however, the surface fluorination resulted in a reduction in both the diffusion and the permeation coefficients by factors ranging between 1.5 and 4.5, depending on the hydrocarbon examined. Modeling of VOC diffusion through a geomembrane/compacted clay composite liner indicated that contaminant impacts were about 1.7-2.9 times lower when a fluorinated geomembrane is used. To achieve the same level of protection as provided by the fluorinated geomembrane underlain by 0.60 m of compacted clay, one would need an additional 0.4-0.9 m of compacted clay in conjunction with a conventional (untreated) geomembrane. The importance of the thickness of the treated layer is highlighted. CE Database subject headings: Geomembranes; Diffusion; Sorption; Volatile organic chemicals; Fluoridation.

The effect of mechanical deformation on the permeation of methylene chloride (MEC), trichloroethylene (TCE) as well as mixtures thereof through linear low-density polyethylene (LLDPE) geomembranes was studied using a new experimental technique. A total of fifty experimental conditions involving five different deformations, five different concentrations and two types of LLDPE geomembranes were evaluated following a full factorial experimental design. Mixtures of TCE and MEC (0.66, 0.50, and 0.34 volumetric fraction) were tested through geomembranes elongated uniaxially (10% and 20%) as well as in the biaxial mode (10% x 10% and 20% x 20%). The breakthrough times for the permeation of TCE and MEC decreased with elongation for both types of geomembranes. A reduction in breakthrough times between 38 and 45% was observed for the permeation of MEC and TCE though geomembranes elongated 20% x 20% in the biaxial mode compared to the nonelongated specimens. Evidence of stress-enhanced transport was also observed as the steady-state permeation rates of MEC increased between 200 and 300% where geomembranes were elongated 20% x 20% in the biaxial mode compared to the nonelongated samples. Enhanced transport of MEC was also noted during the permeation of the MEC-TCE mixtures. DOI: 10.1061/(ASCE)0733-9372(2004)130:12(1468) CE Database subject headings: Geomembranes; Permeability tests; Polyelectrolytes; Solvents; Organic matter; TCE; Experimentation.

An experimental study was conducted to evaluate factors affecting flow rates past soil-bentonite (SB), geomembrane (GM), and composite geomembrane-soil (CGS) vertical cutoff walls. Intact walls and walls containing defects (inadequate keys, windows, and poor joint seals) were studied. For intact cutoff walls, CGS walls had the lowest flow rate, followed by SB and GM walls. CGS walls typically had flow rates as much as 100 times lower than comparable GM walls. Flow rates increased by a factor of 2-160 when the GM walls contained defective joints or the SB walls contained permeable windows. For all wall types, an effective key was required to achieve low flow rate past the wall. For GM walls, under seepage was not effectively controlled when the GM was placed in direct contact with the aquitard. Flow rates for GM walls placed in direct contact with the aquitard were nearly equal to the aquifer flow rate without a wall. Better control of underseepage was possible with SB and CGS walls placed in direct contact with the aquitard because the soft bentonitic backfill conformed to the surface of the aquitard. Hydraulic conductivity of unsealed joints in GM walls was estimated from flow rates past GM walls where a portion of the joint was unsealed. These hydraulic conductivities ranged between 1.8 x 10(super -4) and 5.6 x 10(super -3) cm/s.

The transport properties of aqueous solutions of benzene, dichloromethane, and trichloroethylene through extended polyvinyl chloride and high-density polyethylene geomembranes are investigated. It is found that extension enhances the permeation rates of the penetrants through polyvinyl chloride geomembranes, and the opposite effect is found in the case of high-density polyethylene. This difference in response is attributed to the type of structural change, which occurred as a result of the extension. The diffusivities of a mixture of the three organic solvents through the geomembranes are also determined.

A quasi-two-dimensional partition-diffusion transport model was developed to determine the diffusion coefficient and partition coefficient for various types of geomembranes from measurements of aqueous organic compound concentrations in a confined, double-compartment apparatus with a geomembrane separating the two compartments. The geomembranes tested were high-density polyethylene (HDPE), very low-density polyethylene (VLDPE), and polyvinyl chloride (PVC) and the permeants were mixtures of methylene chloride, toluene, trichloroethylene (TCE), and m-xylene at 10-100 mg/L. The diffusion coefficient increased exponentially with aqueous concentration and decreased exponentially with geomembrane thickness. The partition coefficient was unaffected by compound concentration and membrane thickness. As HDPE geomembranes were stretched by 5% of their original length, the partition coefficient increased by 0.15-0.6 times. VLDPE had 1.8-3.3 times greater partition coefficients and 1.6-2.8 times greater diffusion coefficients than HDPE, while PVC had 6.2-8.3 times greater partition coefficients and 1-1.8 times greater diffusion coefficients than HDPE.

The transient and steady-state mass fluxes were estimated based on partition and diffusion coefficients and compared with fluxes through holes in liner systems under representative field conditions. Stretched high-density polyethylene (HDPE), unstretched very low-density polyethylene (VLDPE), and unstretched poly-vinyl chloride (PVC) had 2.0-2.5, 4.4-5.2, and 8.4-10.8 times greater permeabilities than unstretched HDPE, respectively. The maximum instantaneous mass flux decreased by more than 15 times as the initial aqueous concentration decreased from 100 to 10 mg/L and as the HDPE thickness increased from 0.76 to 2.54 min. The maximum instantaneous mass flux increased by 1.7 times when a HDPE geomembrane was stretched by 5% of its original length. The flux caused by steady-state permeation through the intact geomembrane, which has so far been neglected, was comparable to the flux through the geomembrane with large holes alone but more than three to 34 times greater than the flux through the geomembrane with small holes alone, implying that the permeation through the intact geomembrane may pose serious environmental contamination.

The acceleration and displacement properties of geosynthetic materials were tested to determine if they can be used as base isolation systems. The materials, which were subjected to shaking-table and dynamic centrifuge tests, decreased their sliding resistance with increasing excitation frequency and velocity but the reverse was true when maximum acceleration and relative displacement were reached. Although further research is needed, results of the tests proved that geosynthetic materials can be effective base-isolation systems.

A new index test method, the notched constant tensile load (NCTL) test, for evaluating high-density polyethylene (HDPE) geomembranes regarding stress-cracking resistance is presented in this paper. Eighteen commercially virgin geomembranes and 7 field-exhumed geomembranes were evaluated using the new test. Results show a wide variation in the onset of the transition time. For the 18 virgin geomembranes, the transition times range from 10 hours to 5,000 hours. In addition, all 7 field-exhumed geomembranes, where failure actually occurred, show transition times less than 100 hours. An evaluation of the test results leads to a tentative recommendation that the transition time for an acceptable HDPE geomembrane should be 100 hours or longer. A comparison between the results of NCTL test and the currently used ASTM D 1693 bent-strip test was conducted. It indicates that the bent-strip test cannot adequately evaluate stress cracking resistance, and that the NCTL test is a more critical test in the assessment of such behavior.

R.M. QUIGLEY AWARD The R.M. Quigley Award is given out each year to the best paper published in Canadian Geotechnical Journal (CGJ) in the previous year. Bob Quigley was one [...]

A study of interface shear strengths between smooth and textured high density polyethylene (HDPE) geomembranes (GMs) and a woven/nonwoven needle-punched geosynthetic clay liner (GCL) is presented. Tests were performed using a large direct shear machine capable of measuring peak and large displacement (200 mm) shear strengths. The failure surface was located at the GM/GCL interface for all tests conducted, corresponding to a normal stress range of 1-486 kPa. Small positive pore pressures were measured for all interfaces at peak shear strength. Thus, the practice of preparing failure envelopes using total normal stress, instead of effective normal stress, appears to be conservative. Interface shear strengths for textured GMs placed against the nonwoven side of the GCL were higher than those corresponding to the woven side. By comparison, differences in peak shear strength for laminated and coextruded GM interfaces were relatively less. Limited tests showed that peak and large displacement shear strengths were independent of displacement rate and dependent on the shear direction of the GM. The quantity of extruded bentonite at the interfaces generally increased with normal stress and was less for nonwoven geotextile interfaces than for woven geotextile interfaces. Implications of the findings to the testing of GM/GCL interfaces and the characterization of GM/GCL interface shear strength are discussed.