Presentation is loading. Please wait.

Presentation is loading. Please wait.

Barrier Layers 1. Design considerations Selection of landfill barrier components Cost Slope stability concerns Selection of barrier materials, slope,

Similar presentations


Presentation on theme: "Barrier Layers 1. Design considerations Selection of landfill barrier components Cost Slope stability concerns Selection of barrier materials, slope,"— Presentation transcript:

1 Barrier Layers 1

2 Design considerations Selection of landfill barrier components Cost Slope stability concerns Selection of barrier materials, slope, and thickness Long-term durability Estimation of leachate generation Estimation of permeability Main design consideration: minimize migration of leachate from landfills and remove leachate efficiently 2

3  Clay: low permeability; availability; compaction  Existing soils: existence of fractures and root holes; amend the existing soils with bentonite, fly ash, or cementing materials  Geomembranes/flexible membrane liners (FMLs): polyethylene and polyvinyl chloride; used on their own or as part of a composite system Native material Low permeability liner Drainage layer Leachate mound Refuse Filter fabric (optional) Collection drain Clay liner 3

4 4

5 5 Primary composite liner Secondary composite liner 3 ft compacted clay layer Geomembrane Geonet Geotextile 1.5 to 2 ft compacted clay layer Geomembrane Geonet Geotextile filter 2 ft protective soil layer Waste 2 to 3 ft compacted clay layer 1 ft sand drainage layer Geosynthetic clay liner 1 ft sand or gravel drainage layer Geotextile Geomembrane 1.5 to 2 ft protective soil layer Waste

6 6 1 ft compacted clay layer 6 in sand layer 2 ft compacted clay layer 60 mil geomembrane 4 in leachate collection pipe (placed directly on geomembrane 2 ft sand Waste 2 to 4 ft compacted clay layer 40 to 80 mil geomembra ne 1 ft sand leakage protection layer 40 to 80 mil geomembran e 1 ft sand or gravel leachate collection layer (without and with leachate collection pipes) Geotextile 2 ft soil layer Waste

7 Types of Clay MontmorilloniteMontmorillonite, kaolinite, and illitekaoliniteillite Crystalline Structure of a Clay Silicate tetrahedron (SiO 4 ) and octahedron consisting of aluminum (Al 2 (OH) 6 ) or magnesium (Mg 2 (OH) 6 ) Clay groupsCEC (meq/100 g)Specific surface (m 2 /g)Expansion indexCEC Kaolinite 3 ~ 510 ~ 20 Sodium0.20 Calcium0.06 Illite 10 ~ 4065 ~ 100 Sodium0.15 Calcium0.21 Montmorillonite 80 ~ ~ 840 Sodium2.5 Calcium0.80 There is a tendency for Ca to replace Na in the montmorillonite structure causing shrinkage and the development of cracks. 7

8 8  If a soil contains low plasticity index (≤ 10%), the soil will possess insufficient clay to develop low hydraulic conductivity.plasticity index  A soil with high plasticity index (≥ 30~40%) tends to form hard clods when dried and stick clods when wet.  Recommended PI: 10% ≤ PI ≤ 40% High PI  clay, low PI  silt

9 9  Fine content: Fines are defined as the fraction of soil on a dry weight bases that passes through the openings of No. 200 sieve (0.075 mm).  Maximum particle size: Large particles can interfere with compaction and damage the geomembrane if it is placed on top of a compacted soil linter.  Recommended particle size: < 1~2 inches (~5 mm, No. 4 sieve)

10 10  Bentonite-soil admixture: Bentonite may be added to clay-deficient soils in order to provide a material with low hydraulic conductivity (< 1 × cm/sec).  Recommended bentonite content: 4~6%

11 Clay Liners  Properly select soil in terms of clay content  Use thicker liners to compensate for construction variability  Carefully supervise construction methods and quality control testing  Establish an effective monitoring program to reveal construction flaws before serious problems occur  Use lysimeters in the field to monitor performance Factors affecting compaction  Type of compaction, compactive effort, size of clods, bonding between lifts, moisture contents Optimum water content: saturation between 0.8 to 0.9; 0 to 3% wet of optimum and at compactions equivalent to 95% Standard Proctor (ASTM D698) or 90% modified American Society of State Highway Transportation Organization (ASSHTO T99) Proctor A wet-side compaction: low K because the soil particles are arranged in a dispersed pattern A dry-side compaction: a flocculated pattern, which offers better paths for the flow of water and consequently high K 11

12 12 Sharp decrease in K

13 Plastic clay: more difficult to break and compact in the field, more sensitive, and less time to dry Higher plasticity index: less permeable  Use clay with a plasticity index < 20 for ease of installation and acceptable permeabilityplasticity index Desiccation: causes significant increase in K  Avoid by adding cover soil (> 0.3 to 1 m) or keeping the soil moist by applying water during the periods in which it is exposed;  A clay with a high liquid limit develops more desiccation cracks (  30 ~ 50%)liquid limit Freezing/thawing: causes irreversible increase in K; avoid by adding cover soil or refuse in excess of the frost depth Hydraulic conductivity measurements: in the lab vs. field; exacerbated by the spatial variability of soil properties and placement methods in the field. Liquid limit measurement: 13

14 Ridged-wall permeameter If the structure of the clay changes during permeation, shrinkage, cracking, and/or piping can occur, this can result in increased flow. Flexible-wall permeameter The confining pressure provided in a flexible-wall permeameter can cause the clay to heal despite the structural changes. As a result, little change in K is observed. 14

15 Use landfill leachate. If no leachate exists, use 0.01 N CaSO 4 - added synthetic leachate. If leachate-soil compatibility is not expected to be a problem, the use of flexible wall permeameters with confining pressures similar to those expected in the field is preferred. Field-scale measurement Measure seepage in the field using lysimeters; constructed in and below the liner or in a trial linerlysimeters Double-ring infiltrometers may be employed during construction. 15 Lysimeter

16 16  Construct the liner as a series of layers  Place individual layers in 15 cm (6 in.) lifts at 2 to 3% wet of optimum moisture content to create a 0.7 to 1.3 m (2 to 4 ft) overall thickness in a total of four to eight lifts  Compact each of the 15 cm lifts by a heavy-footed roller (30 tons) making several passes on each lift  Use the roller feet be sufficiently long to work the layer being placed into the layer below to ensure good bonding between the lifts of soil to minimize the formation of lateral flow channels between the lifts. If lateral flow occurs, significant increases in hydraulic conductivity will result.  In situ liner K >> one to two orders of magnitude greater than lab measured K  Total liner thickness: sufficiently thick to avoid construction irregularities (e.g., a min. of 0.75 m)  Commonly use composite liners with a geomembrane over a barrier of natural material (i.e., compacted clay liner)

17 17

18 18 Dumping clayey soil for compaction Soil compaction (steel wheel compactor)

19  Diffusion is more dominant than advection. Diffusionadvection  Diffusion may transport contaminants at rates greater than permeability-dependent advective flow.  Barriers may retard contaminants through the processes of sorption, precipitation, biodegradation, and filtration.  Even though exposure of clay materials to landfill leachates tends to increase permeability, permeability decreases because of the biomass and precipitate accumulation at the clay surface.  Carbonate Dissolution: likely to be modest  Cation Removal: by ion exchange, heavy metals are attenuated (CEC value – important)  Anion Removal: some are poorly attenuated  Other Inorganic Contaminants: no adverse effect on K  Attenuation of Biodegradable Organics: normally removed 19

20  Concentrated organic solvents could alter the structure of clay soils and increase their K’s 100- to 1000-fold but not diluted organic solvents.  Concentrated organic solvents cause shrinkage and cracking of clay soils.  Volatile organic compounds (VOCs) tend to breakthrough quickly. Organic liquid GroupRepresentative liquidsComments on potential interaction Organic acids Acetic acidsMultiple potential attack mechanisms Poor adsorption Organic basesAnilineRapid adsorption onto clays Neutral polarAcetone, methanolCompete with H 2 O ethylene glycol to wet clay Reduce fluid viscosity Adsorption inversely proportional to solubility Neutral nonpolarXylene, heptaneDon’t compete with H 2 O to wet clay Adsorb poorly onto clay 20

21  Compacted clay liners failed to exhibit field values of K of < cm/sec due to inadequate design and installation procedures.  In Wisconsin, K < cm/sec has been achieved through strict design, installation, and quality assurance guidelines.  In metropolitan Toronto, K < cm/sec was achieved.  Heavy metals were retained within the upper 15 cm of a clay liner, with Fe, Zn, Cu, and Pb at background levels beyond the 15 cm depth.  Diffusional transport of Cl - and Na + reached 1.5 m into the clay in 15 years.  Leakage rates of 10 L/1000 m 2 /day, from full-scale landfills with 1.2 to 1.5 m thick clay liners have been reported.  Imcompatibility between MSW landfill leachate and the compacted clay liners has not been a problem.  Liner K often decreased in the field because of sealing due to precipitate formation, solids accumulation, and biomass growth along the upper face of the liner and into cracks and fissures. 21

22 22 Piezometer installed as landfill is being completed or after landfill is completed Landfill Double composite liner Single composite liner Ma

23  In 1982, the U.S. EPA banned reliance on clay liners alone for hazardous waste sites and stated that landfill should have a liner that “prevents migration of leachate during its active life.”  The EPA came to the conclusion that a synthetic membrane leads to “virtually 100% removal efficiency” and therefore specified use of single or double liners using “impermeable” synthetic membranes.  Synthetic membranes = impermeable ??? (permeable to organic compounds)  No synthetic membrane is suitable for all wastes.  Geosynthetic includes:  Geonets: for drainage  Geogrids: for slope stability  Geomembranes: for isolation  Geotextiles: for reinforcement, separation, filtration, and drainage  Geomats: for prevention of erosion of exposed slopes such as landfill caps 23

24  Used for lateral drainage by providing a medium through which the planar flow of fluids can occur.  The geonet has minimal depth, but the grid like character provides extensive flow opportunity. Sand 30 cm Geonet Equivalent hydraulic transmissivity 4.5 mm 24 K = 0.2 m/sec, Thickness = 4.5  m K = m/sec, Thickness = 0.3 m Transmissivities? T= 0.2 × 4.5  = m 2 /sec T= × 0.3 = m 2 /sec

25  Employed in the landfill as filters to prevent the movement of soil fines into drainage systems, to provide planar flow for drainage, or to act as a cushion to protect geomembanes.  Typical K: to cm/sec  comparable to sand and gravels  Leachate drainage pipes should not be wrapped directly in a geotextile because of potential clogging.  Should geotextiles be used on top of the drainage media or as underlay or drainage underblanket? Ref. Laboratory studies of clogging of landfill leachate collection and drainage systems by Fleming and Rowe  Ensure that the initial lifts of waste being placed on top of the leachate collection system have a low fines content.  Sensitive to ultraviolet light 25

26  Very low-permeability membrane liners used with any geotechnical engineering materials so as to minimize fluid flow across them.  Intended to limit the movement of leachate  Thicknesses: 0.75 mm (30 mil) to 3.00 mm (120 mil)  Due to failure of some smooth-surface membranes along the shear plane, textured geomembranes are used to minimize slippage of the geomembrane /soil interface. 26

27  Polymers  Filters  Plasticizers  Carbon black  Additives  Scrim reinforcement 27

28  Thermoplastics  Soften upon heating and can be molded  e.g.: polyvinyl chloride (PVC), thermoplastic nitrile (TN-PVC)  Crystalline thermoplastics  Polymeric chains folded in a crystal lattice, forming lamellae (plate-like crystals)  e.g.: low-density polyethylene (LDPE), very low- density polyethylene (VLDPE), high-density polyethylene (HDPE), polypropylene, and elasticized polyolefin 28  Non-crystaline tie-molecules connect lamellae:  More tie-molecules: flexibility

29  Thermoplastic elastomers  Can be molded  e.g.: chlorinated polyethylene (CPE), chlorosulfonated polyethylene (CSPE or Hypalon), and thermoplastic ethylene- propylene diene monomer (T-EPDM)  Elastomers  e.g.: butyl rubber or isoprene isobutene rubber, ethylene propylene diene monomer (EPDM), neoprene, and polychloroprene 29

30 A Geomembrane-Lined Landfill for Special Hazardous Waste (over 3 Million ft 2 of Textured 80 mil HDPE) 30

31  Ultraviolet degradation  UV radiation breaks polymer chains, make membrane brittle  Swelling  Exposure to liquids causes polymers to swell  Oxidative degradation (aging)  Oxygen reacts with polymers, makes membrane brittle rather than flexible  Note: This takes 100’s of years, accelerated by heat  Delamination  Separation of polymer layers  Extractive degradation  Extraction of particular component (such as plasticizer) from polymer  Chemical degradation  Reaction of leachate components or organic chemicals with liner 31

32  Fillers: used to reduce the cost and increase the stiffness without altering the permeability - mineral particles, metallic oxides, fibers, and reclaimed polymers (1~200  m)  Processing aids: used to reinforce or soften the compound during the manufacturing process  Plasticizers: used to impart flexibility to the compounds, although some plasticizers attract microorganism attack  Carbon black: used to impart a black color to the compound which retards aging by ultraviolet light from the sun and increases the stiffness of elastomeric compounds  Fungicides and biocides: used to prevent fungi and bacteria from attacking the polymer  Antioxidants: used to reduce the aging effect of ultraviolet light and ozone  Scrim reinforcement: used to increase the strength and improve tear and puncture resistance; typically nylon or polyester 32

33  Semi-crystalline thermoplastic  Typical content  97% polyethylene  3% carbon black (for UV protection)  Traces (up to 1%) of stabilizers and antioxidant  Extruded  Properties  Most chemical resistant liner material  Low permeability  UV resistant (especially with carbon black and antioxidant)  30~140 mil-thick  Most widely used geomembrane 33

34  Semi-cystalline thermoplastic  Also called very flexible polyethylene (VFPE)  More flexible than HDPE – used for non-uniform surfaces such as lagoons, pond liners, and landfill caps  Extruded  Properties  Withstands tension, high elongation capability  Puncture and stress-crack resistant  Good chemical resistance  Low permeability  Good UV resistance  40~100 mil-thick 34

35  10~20% of thickness from HDPE – for chemical resistance  LLDPE for flexibility  Molten polyethylene bonds at molecular level: not a laminate  Applications  White/black coextrusion for exposed geomembranes (white side to sun to reduce temperature) 35 HDPE LLDPE

36  High/low carbon co-extrusion: high-carbon layer can carry an electrical current 36 Brass wand Electrical charge is applied to high-carbon layer on underside – brass wand brushed on surface will spark at any holes.

37  Usually scrim-reinforced for high tensile strength (fPP-R)  36 or 45 mil-thick  Used for floating covers on surface impoundments, other high stress applications  Good chemical, UV resistance 37

38  One of the earliest geomembranes  Typical mix  35% resin, 30% plasticizer, 25% filler, 5~10% pigment, 2~3% additives  Properties  Good puncture resistance  Good chemical resistance (for non-polar compounds only)  Excellent flexibility  Easiest material to install, easier seam formation using solvents  Low cost 38

39  Thermoplastic elastomer: polymers cross-linked with sulfur compounds  Always scrim reinforced (CSPE-R)  Also an early geomembrane  Used for exposed conditions like floating covers and uncovered waste liners due to UV resistance  Thermoplastic initially: polymers crosslink over time and become thermosetthermoset  Properties  Very good chemical resistance (except aromatic hydrocarbons)  Excellent UV and temperature resistance  Fair to good tear, puncture resistance  Solvent or thermal seam  36 or 45 mil-thick 39

40  Good resistance to UV and oxidation  Good temperature performance  Low strength: butyl rubber  High strength: EPDM  Poor chemical resistance  Difficult to seam  Applications  Roofing  Impoundments 40 Butyl rubber EPDM

41 HDPE: High density polyethylene VLDPE: Very low density polyethylene PVCPVC: Polyvinyl chloride CSPE-R: Chlorosulfonated polyethylene with fabric reinforcement Type Resin % Plasticizer % Filler % Carbon black or pigment % Additives % Density g/cm 3 Width Thickness mil HDPE VLDPE PVC CSPE 95~98 94~96 50~70 40~ ~35 0 0~10 40~50 2~3 2~5 5~ ~1 1~4 2~5 5~ ~ ~ min ’ or 30’ 15’ 40’~80’ 30~140 30~100 10~60 Properties of Geomembranes Market share:  HDPE & Very Flexible PE (VFPE) (60 mil): 60~65%  PVC (30 mil): 35~40% 41

42  Extrusion  Molten polymer is extruded in a non- reinforced sheet  Spreading  Coating of fabric with polymer  Calendering  Heated polymer passed through series of rollers  Sometimes with two sheets or with scrims 42 Extrusion

43  Variety of physical and chemical tests to evaluate materials  ASTM methods for:  Tensile strength (ASTM D638)  Tear resistance (ASTM D1004)  Puncture resistance (ASTM D4833)  Low-temperature brittleness (ASTM D746)  Stress crack resistance (ASTM D1693)  Permeability  Carbon black content and diffusion (ASTM D1603 and D2663)  Accelerated heat aging (ASTM D573, D1349)  Density (ASTM D1505 or D792)  Melt flow index (ASTM D1238)  Thickness (ASTM D5199)  Ply adhesion (ASTM D413) 43

44 Source: U.S. EPA, Seminar Publication: Design, Operation, and Closure of Municipal Solid Waste Landfills. Report Number EPA/625/R-94/008, Center for Environmental Research Information, U.S. Environmental Protection Agency, Cincinnati, Ohio. September (http://www.epa.gov/ORD/NRMR L/Pubs/1994/625R94008.pdf )http://www.epa.gov/ORD/NRMR L/Pubs/1994/625R94008.pdf 44 Multi-axial stress vs. strain for five geomembrane materials (Frobel, 1991).

45  Critical factor for minimizing leakage  Required durability/polymeric properties: UV stability, chemical stability, freeze-thaw stability, biological stability, specific gravity, color, and water sorption  Required mechanical properties: tensile modulus, ultimate tensile strength, ultimate elongation, burst strength, puncture strength, and creep strength  Methods  Thermal seaming  Chemical seaming  Extrusion or fusion welding  Mechanical methods 45

46  Works with thermoplastic geomembranes only (including crystalline thermoplastic)  Techniques  Hot wedge (or knife)  Used for long seams  Requires 4~6 inch overlap  Traveling vehicle moves along seam, heating top and bottom membrane  Hot air bonding  Dielectric bonding (not a field technique) 46 Air pocket For non-destructive testing

47 For thinner, more flexible geomembrane such as 40-mil thick PVC 47

48 Step 1  Membrane is welded in first pass using heat from hand weld hot air device and pressure with the hand 48 Step 2  The weld continues in the mid- portion of the overlap in a manner similar to that in Step 1. Step 3  The weld is finalized by continuing application of heat and sealing edge with roller.

49  Requires that the channel between the two welds be sealed at both ends and inflated to 30 psi (2 bar)  Test results are positive when the pressure does not fall more than 5 psi (.33 bar) in 10 minutes.  The pressure in the channel stresses the weld providing evidence of its integrity. 49

50  Use with HDPE  Welder extrudes a ribbon of melted HDPE (extrudated)  Used for patches  Usually pre-heat pieces to be joined so that membrane will also melt and fuse with extrudate 50

51 51 Lap seam Lap seam with gum tape Tongue and groove splice Extrusion weld lap seam Fillet weld lap seamDouble hot air or wedge seam

52  Fishmouths:  Wrinkles perpendicular to seam  Should be cut along wrinkle ridge, welded, and then patched over  Cold weather and hot weather  Compromises seam quality  Rain or fog  Seams should be free of moisture and clean 52 Reference website for chemical resistance and mechanical properties of various geomembranes:

53  Trial welds  Welding of scrap pieces of geomembrane followed by destructive testing of three 1-inch wide samples  Field tests  Seam tests  Vacuum tests  Destructive tests 53

54 Shear test 54 Peel test

55  Used on double-track welds  Seal both ends with air injection needle welded in  Pressurize void between dual-track welds to 24 to 35 psi  Pressure should remain stable, indicating no leaks  Cut end opposite needle: void should depressurize, demonstrating no blockage of channel 55 Reference for seam tests: See

56  Vacuum box with gasket, viewing window  Soapy solution applied to seam  Vacuum box placed on top, depressurized to reach 3~5 psi  For a period of approx. 15 seconds, examine the geomembrane through the viewing window for the presence of animated soap bubbles  If seam leaks, bubbles will be apparent 56 ASTM D (2006) Standard Practice for Geomembrane Seam Evaluation by Vacuum Chamber See

57  Approximately one test per 500 ft of seam  Patch of seam cut out, ten 1-inch samples created  Five samples for shear strength and five for peel strength. To be acceptable, four out of five specimens must pass.  Keep number of tests to minimum: locations of samples must be patched 57 See 13.2

58  Layer of clay between two geotextiles or glued to geomembrane  Manufactured with bentonite  Bentonite clay [sodium bentonite in the U.S. {5 kg/m 2 (  1 lb/ft 2 ) sodium bentonite}; calcium bentonite elsewhere]  Bentonite has a thick double layers and high swelling capacity  Water is adsorbed until crystal sheets dissociate and form a gel with thixotropic (becoming liquid when disturbed) properties  K = cm/sec  Produced in 4~5 meter (13~16 ft) panels, 20~60 meters (66~197 ft) long 58

59  Geotextile encased: sandwich of geotextile:clay:geotextile  Adhesive bonded: clay is mixture of clay and adhesive to hold sandwich together  Example: Claymax 200R, Claymax 600CL  Stitch-bonded: held together with parallel rows of stitches  Example: Claymax 500SP  Needle-punch: held together with fibers punched through, sometimes bonded to geotextile  Example: Bentomat, Bentofix  Geomembrane-supported – sandwich of clay and geomembrane  Held together by adhesive mixed into clay  Example: Gundseal  Bentonite swelling seals GCLs  Many types self-seal at overlaps; for some types, extra bentonite is applied to overlap  GCLs need to be covered quickly to prevent rapid hydration and uneven swelling and self-sealing 59

60  Increase with increasing compression (up to order of magnitude  Dessication increases K: K recovers upon rehydration  K relatively insensitive to freeze-thaw  If permeated by organic liquid prior to hydration, bentonite does not hydrate and swell and therefore does not achieve low K. 60

61  Easier and faster to construct, with lightweight equipment  Simpler quality assurance (QA)  Comparable in cost to clay liner  Clay: $0.50 to $5.00 per ft 2  GCL: $0.42 to $0.60 per ft 2  Small thickness conserves landfill space  Better freeze-thaw, desiccation resistance  Withstand differential settlement better than clay liners 61

62 62 Potential failure surfaces 1.Interface between upper surface of GCL and overlying material 2.Internal failure within GCL (can be within bentonite or at the internal interface between bentonite and a geosysthetic 3.Interface between lower surface of GCL and overlying material

63  Less shear strength  Less attenuation capacity  Faster diffusive breakthrough  Thin GCL more subject to puncture  Limited experience 63 Currently, GCLs are generally well accepted for use in landfill covers and are gaining acceptance for use as containment liners.

64  Permeation: occur at molecular level  Major leakage for volatile organic (nonpolar) compounds (VOCs) but not for water or polar compounds  Pinholes: defined as holes with diameter < liner thickness  Originate in manufacturing  Usually negligible source of leakage  Holes: openings with diameter > liner thickness  Sources: defective seams, seam failures, punctures, and construction damage 64

65 PolymerThicknessTransmission (mm)(mil)(g/m 2 /day) PVC PVC PVC CSPE HDPE HDPE

66 SolventTransmission rate (g/m 2 /day) Water vapor0.017 Methyl alcohol0.16 Acetone0.56 Cyclohexane11.7 Xylene21.6 Chloroform

67 PropertyHDPECSPEPVC Heat resistance Microbial resistance Chemical resistance UV resistance Puncture resistance Ease of placement Cost Tensile strength Cold weather problems 67  ~       ?    ModerateHighLow  ?  -   Source: McBean, E. A., F. A. Rovers, and G. J. Farquhar, Solid Waste Landfill Engineering and Design. Prentice Hall PTR, Upper Saddle River, New Jersey.

68  Darcy’s equation for geomembrane permeability  Poiseuille’s equation for pinholes (during manufacturing)  Bernoulli’s equation for large holes (during installation) Q = ca  2gz where Q = discharge (m 3 /sec); Q/A = discharge per unit area (m/sec); z = leachate mound height (m); K = hydraulic conductivity (m/sec); T = thickness (m); d = pinhole diameter (m); a = hole surface area (m 2 );  = density of water (kg/m 3 );  = dynamic viscosity of water (kg/m·sec); g = gravity acceleration (9.81 m/sec 2 ); and c = dimensionless coefficient (= 0.6). Q z A T = K  gzd  T Q = 68 Not valid when K is low (i.e., geomembrane K  cm/sec)

69 Conditions:  1 cm 2 hole (or area) per 4000 m 2 (i.e., 1 hole per acre)  Leachate mound height z: 0.3 m 3 cm30 cm Geomembrane/clay110 Geomembrane/silt10100 Geomembrane/sand3001,500 Geomembrane/gravel or geonet6002,000 Hydraulic head Typical leakage rates through the primary liner (L/hectare/day) 69 Reference:

70 1 cm 2 pinhole/acre → m Φ pinhole × 510 hole 1 cm 2 pinhole/acre → m Φ pinhole 70

71 When a geomembrane is underlain by low permeable media for a circular defect, Q=0.976C qo [1+0.1(h/t UM ) 0.95 ]d 0.2 h 0.9 k UM 0.74 (1) C qo = dimensionless coefficient that characterizes the quality of contact between the geomembrane and the underlying medium (good = 0.21, poor = 1.15); h = leachate head, m; t UM = thickness of the low-permeability medium underlying the geomembrane. m; d = defect diameter, m; and k UM = hydraulic conductivity of the low-permeability medium underlying the geomembrane, m/sec. 71

72 72 When a geomembrane is overlain and underlain by infinitely permeable media (Bernoulli’s Equation), Q=0.6a  2gh = 0.15  d 2  2gh (2) a = defect area (m 2 ). When a geomembrane is underlain by an infinitely permeable medium, (3) Giroud, J.P., Soderman, K.L., Badu-Tweneboah, K. (1998) New Developments in Landfill Liner Leakage Evaluation.

73 Eq. 1 Eq. 2 Eq. 3 73

74 q i =rate of leachate supply rate on top of the medium overlying the geomembrane Hydraulic conductivity of the medium overlying the geomembrane 74

75 q i = leachate supply rate L = horizontal projection of the length of the leachate collection layer in the direction of the slope β = slope angle of the permeable medium L  & (  & k OM )  → Q  At a given situation defined by L, , and q i, k OM  → Q  75

76 Q = kt o 2 (19) (20) k = hydraulic conductivity of leachate collection layer, L/T t o = max. thickness of leachate in the leakage collection layer Leachate head 76

77 77 Park, J.K., Sakti, J.P., and Hoopes, J.A. “Transport of Aqueous Organic Compounds in Thermoplastic Geomembranes. II. Mass Flux Estimates and Practical Implications,” Jour. of Environ. Eng., ASCE, Vol. 122, No. 9, pp , Permeation >> LeakageOrganic compound transport:

78 https://www.youtube.com/watch?v=J9k98ChAisI 1. Positioning the roll of geomembrane over the deployment trailer with an excavator or loader lifting capacity min. 4,000 lbs. 2. Deployment from the base to top of slope with a block and cable from a fixed object. Overlap controlled from the base of cell and alignment. Slope angle 2.5:1 78

79 79 ASTM D Standard Guide for Mechanical Attachment of Geomembrane to Penetrations or Structures ISO 9001:2000 Geomembrane Installation Guide 1. Positioning the roll of geomem- brane over the deployment trailer with an excavator or loader lifting capacity min. 4,000 lbs. 2. Deployment from the base to top of slope with a block and cable from a fixed object. Overlap controlled from the base of cell and alignment. Slope angle 2.5:1

80 3. Membrane positioned throughout the base and slope areas. Sandbags placed to control wind uplift and expansion & contraction on site. 4. Preparation of the base /slope seam complete with a HDPE runner to assist in field welding over poor or wet soil conditions. 80

81 5. A 2" prequalification strip of membrane is taken from an extrusion weld or a wedge weld seam and is tested with a portable laboratory tensiometer. 6. After the wedge welder is qualified with test seam strip, it is placed within the seam for field welding. Technicians monitor the wedge welder's performance as it travels up the slope area. 81

82 7. Wedge welder in the butt seam placing slack wrinkle within the lining system. Control of slack and potential bridging of membrane are critical factors for field installation. 8. Non destructive testing of wedge welded field seams with central air channel. Seam is pressurized and stabilized for a 10~15 minute cycle. 9. Extrusion welder is qualified before completing any patching or "T" sections of wedge welded panels. Extrusion gun is also used for detail work and penetrations. 82

83 Welds HDPE, LDPE, TPO, PVC, XR-5 and HYPALON 83

84  Quality assurance: a planned and systematic pattern of all means and actions designed to provide adequate confidence that items or services meet contractual requirements and will perform satisfactorily in service  Quality control: those actions that provide a means to measure and regulate the characteristics of an item or service to contractual and regulatory requirements  QA/QC for placement of membrane liner  Prepare a subgrade that is firm, flat and free of sharp stones, gravel or debris  Use a qualified installation contractor  Follow manufacturer’s recommended procedures for the adhesive system and seam overlap  Conduct installation during dry and temp. between 5~40  C  Plan and implement a quality control program  Document inspection for review and record keeping 84 ttachmentII-9.pdf

85  Optional filter material: separates the bottom portion of waste from the leachate collection and drainage medium, to reduce clogging of the drainage system  Drainage layer: must have high transmissivity and resist plugging; gravel dia. > 38 mm  Protector layer: prevents materials in the drainage layer from puncturing the primary geomembrane liner; a thick needle-punched geotextile (filter fabric)  Barrier layer: frequently a geomembrane or a natural soil liner or a combination of both; geosynthetic clay liners (GCL)  Leak detection system: identifies leakage from the primary liner system and enables it to be collected and removed  Secondary barrier (geomembrane): last defense against leachate escape  Subgrade soil: native material 85

86  A min. of 2 ft thick clay (50~70% by wt passing 200 sieve and K< cm/sec) cap is frequently required above the venting and drainage layer to provide a low hydraulic conductivity barrier to percolation.  Constructed in max. 6-in. lift heights after the soil is compacted to at least 95% Standard Proctor Density with successive layers worked together by a sheepsfoot roller with at least 6+ inch feet, and then proof- rolled flat. Desirable properties of a cap material  Resist biological attack  Retard gas permeation  Be impermeable to percolated surface waters  Have sufficient friction characteristics to prevent cover soils from slipping and cracking open  Resist diminishing physical properties due to long-term soil burial  Should not impede vegetative growth  Not deteriorate under UV light if exposed for significant length of time  Retain physical properties over a broad range of temperatures  Accommodate localized settlement without rupture 86  Retard random permeation  Be critter resistant

87 87

88 88


Download ppt "Barrier Layers 1. Design considerations Selection of landfill barrier components Cost Slope stability concerns Selection of barrier materials, slope,"

Similar presentations


Ads by Google