GCL Design Guide - The Geosynthetic Institute

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Criterion Hydraulic Conductivity - GCL - Seam Long-term stability - Geotextile - Geofilm or Geomembrane - Bentonite Intimate contact Contaminant flow Landfill Covers 1 1 1 1 1 3 3 Table 1 – Subjective Ratings for Importance of Various Criteria of Common GCL Applications Landfill Base Seals 1 2 1 1 1 1 1 Dams/Dykes (GCL only) 1 1 1 1 1 4 4 Waterways (GCL only) 1 1 1 1 1 4 4 Surface Impoundments (GCL only) 1 1 1 1 1 4 4 Environmental Protection 1 1 1 1 1 GCL only: 4; Comp: 1 GCL only: 4; Comp:1 Secondary Containment 1 1 1 1 1 GCL only: 4; Comp: 1 GCL only: 4; Comp:1 Diffusion 3 1 4 4 4 2 GCL only: 4 4 Comp: 2 Settlement 1 2 3 3 2 3 2 1 Behavior - Freeze/thaw 2 1 1 1 2 1 1 - Dry/wet Shear - Internal 1 - Interface 1 Puncture Resistance - Fine cover 3 - Sandy gravel 2 - Coarse cover 1 Internal Erosion - GT < 250 g/m 2 4 - GT > 270 g/m 2 4 Bearing behavior (installation) 30/60/90 cm Cover 1 4 (1 if not frost protected) 4 (2 if not protected against dry/wet cycles) 1 1 Normally covered with geomembrane 3 3 1 1 1 3 2 1 1 2 3 1 1 3 2 1 1 2 1/2/3 Normally GM covered 1/2/3 1/2/3 1/2/3 1/2/3 1/2/3 1/2/3 Soil thickness Root penetration 1 4 2 2 2 1 1 1 1 – important 2 – project dependent requirement 3 – rarely required 4 – not relevant GM – geomembrane GT – geotextile [Comp = Composite GM/GCL liners] 2 1 1 3 2 1 1 2 2 1 1 3 2 1 1 2 1 1 1 3 2 1 1 2 Waste Covers 1 1 1 1 1 1 1 1 3 2 1 1 2 GCL5 - 6 of 34 Rev. 1: 1/9/13
5. Major GCL Applications 5.1 This guide describes the major issues, as well as selected related design issues, and the various types of GCL tests for the following applications. Note 4: Note 5: Multicomponent GCLs might improve the performance over a standard GCLs in a specific application. However, they might only be suitable for short- or mid-term use. A geomembrane overlying a GCL, i.e., a GM/GCL composite, is always an alternative for long-term use in most applications. 5.1.1 Landfill Covers (or Caps) and Remediation Barriers—GCLs are used to inhibit the ingress of water and the escape of fluids and/or gases in the construction of solid or industrial waste facility cover or to cap contaminated soil. The typical confining stress is in the range of 10 and 50 kN/m 2 . Hydraulic gradients are typically less than 50. 5.1.2 Landfill Base (or Bottom) Liners—GCLs are used to limit the escape of landfill leachate or gases in the construction of solid waste storage, heap leach pads, and disposal site base liners and to inhibit the ingress of groundwater. Confining stresses vary greatly, e.g., 100 and 1000 kN/m 2 . The hydraulic head acting on the GCL in a well performing landfill base liner is usually regulated to be less than 300 mm. Thus, for a typical GCL thickness of 7 to 10 mm, the hydraulic gradient is typically less than 50. That said, conditions vary widely. 5.1.3 Canals, Streams, or Waterways Liners and Surface Impoundments or Ponds—In applications in which a significant water head is maintained, GCLs are generally used in combination with an existing soil barrier or in combination with a geomembrane, i.e., a GM/GCL composite. Under certain conditions they can be used alone. In all cases, the function of the GCL is to reduce seepage through the system thereby reducing water loss from the waterway or storage impoundment. The typical soil stress is less than 50 kN/m 2 , however, the head acting on the GCL invariably exceeds 1 m. As a result, the hydraulic gradient is then higher than 100 and can even be 1000, or more, depending on site specific conditions. 5.1.4 Environmental Protection—The function of the GCL in these applications is to inhibit hazardous liquids or constituents resulting from vehicle, railway, or airline incidents from entering a sensitive location in the local environment. A GCL as the sole hydraulic barrier or a GM/GCL composite will often be used. The typical confining stress is in the range of 50 kN/m 2 and the hydraulic gradient is often less than 50. 5.1.5 Secondary Containment—The function of the GCL in this application is to inhibit hazardous liquids or constituents stored in storage tanks, silos or GCL5 - 7 of 34 Rev. 1: 1/9/13
Page 1 and 2: Geosynthetic Institute 475 Kedron A
Page 3 and 4: 2.3 ISO Standards 3. Terminology IS
Page 5: etween geotextiles (occasionally a
Page 9 and 10: landfill cover (cap) applications i
Page 11 and 12: 6.7 Covers for Mine Wastes, Tailing
Page 13 and 14: 8.2.2 Internal Reinforcement Streng
Page 15 and 16: against or within the bentonite. As
Page 17 and 18: 10.1.1 GCL Barrier—The flow rate
Page 19 and 20: 10.2.4 ASTM D 6766 is used to deter
Page 21 and 22: found essentially no change in the
Page 23 and 24: Longitudinal slope tensioning of GC
Page 25 and 26: Gilbert, R. G., Fernandez, F. and H
Page 27 and 28: Rowe, B. T. and Daniel, D. E. (1996
Page 29 and 30: Fig. 1 - Solid Waste Containment Sy
Page 31 and 32: Fig. 5 - Examples of Exposed Mine W
Page 33 and 34: Fig. 8 - Variation of Hydraulic Con

GCL Design Guide - The Geosynthetic Institute

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