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March 27, 2019Follow Us: NTH Consultants
2019 ESD/MWRA 29th Annual Solid Waste Technical Conference
Lansing, MI
PRESENTED BY:
David R. Lutz, P.E.
Back to Basics:Landfill Liner and Cover Systems
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What Will We Cover?
2
• Brief Background and History of Liners
• Types of Liners and Engineering Considerations– Composite System
– Drainage Layer
– Base Liner
– Final Cover
• Technological Advances
• Additional Resources/Questions
3
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BACKGROUND AND HISTORY• Liner System: An engineered barrier to
limit migration of contaminants to the environment
• Subtitle C (40 CFR 264) - 1982: Type I hazardous landfill (MI-Part 111)
• Subtitle D (40 CFR 258) – 1991: Type II non-hazardous landfill (MI-Part 115)
• Double Liner Vs. Single Liner
• Composite System = Drainage + Synthetics + Low Permeability Barrier (natural or synthetic) + Native
Liner Systems
5
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Liner Systems: Overview
Native Soil
Base LinerFinal Cover
6
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Liner Systems: Base System Overview
Single Liner Double Liner
7
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Liner Systems:Drainage Layer
• Function– Drain Leachate to Sump for Removal
– Maintain Less than 12” of Head on Liner – Mounding Calculation
– Protective Cushion over Liner
• Materials– Sand or Stone – Silica Based, Natural
– Synthetic• Geonet, Geocomposite
– Combination
– Alternatives: Tire Shred, Auto Fluff, Blast Furnace Slag, other…
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Liner Systems:Drainage Layer
8
• Considerations– Permeability/Transmissivity
– Availability
– Natural Materials• Fines (<#200)
• Carbonate Content – Leaching
– Synthetic Materials• Interface Friction/Slope Stability
• Factoring in Biologic/Chemical clogging, impingement, core creep reduction
• UV Degradation
• Seaming
9
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Liner Systems:Base Liner
• Function– “Impermeable” Barrier to Leachate
– Composite• Synthetics
• Installed Low-Permeability Layer
• Native Low-Permeability Layer
• Materials– Synthetics
• HDPE, LLDPE, PVC, EPDM, Others…
• Textured, Smooth, Reinforced
• Seamed
– Low-Permeability Layer• Geosynthetic Clay Liner
• Re-compacted Clay Soil9
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Liner Systems:Base Liner - Synthetics
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• Considerations– Chemical Compatibility with
Leachate
– Interface Friction/Slope Stability
– Differential Settlement Tolerance
– High Temperature Tolerance
– Exposure – UV Degradation
– Proper Installation (QA/QC)
– Protection during In-Service
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Liner Systems:Base Liner – Low Permeability Layer
11
• Considerations– Geosynthetic Clay Liner (GCL)
• Chemical Compatibility with Leachate
– Polymer-enhanced Bentonite
• Exposure – Seam Separation– Appropriate Overlap
– Loose Bentonite Augmentation
• Interface Friction/Slope Stability– Carrier Fabric
– Internal Shear Strength
» Method of Construction
– System Stability
– Compacted Clay Liner (CCL)• Availability/Quality
• Moisture Conditioning/ Desiccation– Desiccation = Increased Permeability
• Differential Settlement– Fissures = Increased Permeability
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Liner Systems: Cover System Overview
Type III(Mono/C&D) Type II (Municipal)
Type I (Hazardous)
• Composite System (Typically)– Multiple Material Variations
and Configurations
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Liner Systems:Final Cover
13
Veneer Slope Stability
Uniform Cover Soil Thickness with the Incorporation of Equipment Loads
Calculation of FSActive Wedge:
Wa= 369.6 kN
Na= 350.7 kN
Passive Wedge:Wp= 7.3 kN
a= 191.8
b= -404
c= 22.0
FS= 2.05
thickness of cover soil = h = 0.46 msoil slope angle beneath the geomembrane = b = 18.4 ° = 0.32 (rad.)
finished cover soil slope angle = w = 18.4 ° = 0.32 (rad.)length of slope measured along the geomembrane = L = 40.2 m
unit weight of the cover soil = g = 20.9 kN/m^3friction angle of the cover soil = f = 15.0 ° = 0.26 (rad.)
cohesion of the cover soil = c = 95.4 kN/m^2 C= 138 kN
interface friction angle betw een cover soil and geomembrane = d = 10.3 ° = 0.18 (rad.)
adhesion between cover soil and geomembrane = ca = 3.9 kN/m^2 Ca= 150 kN
thickness of cover soil = h = 0.46 m b/h= 1.8
equipment ground pressure (= tire pressure) = q = 400.0 kN/m^2 We=qwI= 270.8
length of each equipment tire = w = 0.7 m Ne=Wecos b = 257.0
width of each equipment tire = b = 0.8 m Fe=We (a/g) = 0.0
influence factor* at geomembrane interface = I = 0.97acceleration/deceleration of the scraper = a = 0.00 g
Note: numbers in boxes are input values
numbers in Italics are calculated values
FS = -b + b2 - 4ac2a
W
b
A
NA
h
E PEA
NP
C
Passive Wedge
WP
N ta nfp
GM
We
Ne
Fe
L
Ac tive Wedge
Cover SoilThickness
Equipment Track Width
Very Wide Wide Standard
² 300 mm 1.00 0.97 0.94
300-1000 mm 0.97 0.92 0.70
³ 1000 mm 0.95 0.75 0.30
*Influence Factor Default Values
• Function– Environmental Barrier
– Limit Precipitation Infiltration
• Materials– Composite System – Similar To Base
Liner
• Considerations– Interface Friction/Slope Stability
– Gas Venting
– Internal Drainage
– Stormwater Management/ Erosion Control
– Differential Settlement: Material Selection
– Construction Technique: Equipment Direction
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Liner Systems:Final Cover – Veneer Stability
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Liner Systems:Final Cover Considerations
• Management of Water– Internal Drainage
• Limit Excessive Pore Pressure Buildup -> Stable Slope
– Stormwater Management• 25-Year/24-Hr Storm
• Manage Runoff
– Erosion Control• Soil Loss < 2 Tons/Ac
– Diversion Berms/ Swales
• Erosion Control Products– Rip-Rap
– TRM/Blankets
– Seed Mixture Selection
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Technological Advances
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Liner Systems:Technology Advances
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• “System” Products– Closure Turf
• Synthetic Grass
– Super Gripnet• Combined Geomembrane/Geonet
– DrainTube• Geocomposite/Drainage Layer
• Gas and/or Liquid
– Permeable Caps• Multi-Layer
• Evapo-transpiration
• Climate Dependent
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Liner Systems:Technology Advances
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• Liner Products– Leak Detection Geomembranes
• Conductive Layer for Spark Testing (D7240)
– Exposed Geomembrane Covers• Eliminate Protective Cover Layers
• UV Degradation, Stormwater Control and Uplift Considerations
– Solar Panel Integration
– Erosion Control Products
– Specially formulated stabilizers/ polymers/ enhancers for site-specific considerations of different materials
References/Questions
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References/Questions
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• Resources– GRI: Geosynthetic Research Institute
• https://geosynthetic-institute.org/
– FGI: Fabricated Geomembrane Institute• https://www.fabricatedgeomembrane.com/
• Free Webinars
– Manufacturers
– Books• Geotechnical Aspects of Landfill Design and
Construction, (2002), Koerner et. al.
• Designing With Geosynthetics 6th Ed., (2012), Koerner
• Questions?
