Chapter 17 Landfill Liners and Geosynthetics 연세대학교 지반공학연구실

17 Landfill Liners and Geosynthetics ▶ Waste materials can be classified into four categories : municipal waste, industrial waste, hazardous waste, and low-level radioactive waste

17 Landfill Liners and Geosynthetics ▶ Leachates are a main source of ground water pollution, therefore, they must be properly contained in all landfills, surface impoundments, and waste piles, within some type of liner system.

17.1 Landfill LinersOverview ▶ Until about 1982, Liner material used in landfill – Clay ▶ In 1984, U.S. Environmental Protection Agency’s minimum technological requirement for hazardous waste landfill design and construction by U.S. Congress in Hazardous & Solid Waste amendments - double liner system ▶ Review the general properties of the component materials involved in the system – that is clay soil and geosynthetics (given in the following sections)

17.2 Compaction of Clay Soil for Clay Liner Construction ▶ Figure 17.1 shows the results of laboratory compaction tests on a clay soil as well as the variation of hydraulic conductivity on the compacted clay specimens. From the laboratory test results shown, the following observations can be made : For a given compaction effort, the hydraulic conductivity, k, decreases with the increase in molding moisture content, reaching a minimum value at about the optimum moisture content (that is, approximately where the soil has a higher unit weight with the clay particles having a lower degree of flocculation). Beyond the optimum moisture content, the hydraulic conductivity increases slightly For similar compaction effort and dry unit weight, a soil will have a lower hydraulic conductivity when it is compacted on the wet side of the optimum moisture content

17.2 Compaction of Clay Soil for Clay Liner Construction ▶ Benson and Daniel (1990) : the magnitude of k decreases with the decrease in clod size ▶ To prevent groundwater pollution from leachates generated from solid-waste disposal sites, the contractor must ensure that the soil meets the following criteria (EPA, 1989) : The soil should have a least 20% fines (fine silt and clay-sized particles). The plasticity index (PI) should be greater than 10. Soils that have a PI greater than about 30 are difficult to work in the field. The soil should not include more than 10% gravel-sized particles. The soil should not contain any particles or chunks of rock that are larger than 25 to 50mm(1~2 in).

17.2 Compaction of Clay Soil for Clay Liner Construction  

17.2 Compaction of Clay Soil for Clay Liner Construction ▶ Bonding between successive lifts is also an important factor. As is shown schematically in Figure 17.2 Poor bonding can increase substantially the overall hydraulic conductivity of a compacted clay.

17.2 Compaction of Clay Soil for Clay Liner Construction  

17.3 Geosynthetics ▶ The term geosynthetics includes the following : Geotextiles Geomembranes Geogrids Geonets Geocomposites

17.3 Geosynthetics ▶ Five major function Separation Reinforcement Filtration Drainage Moisture barrier ▶ For further information, refer to a geosynthetics text such as that by Koerner (1994).

17.4 Geotextiles ▶ Geotextiles are textiles in the traditional sense ; - however, the fabrics are usually made from petroleum products. They may be woven(직포), knitted(편물), or nonwoven(부직포), or needle-punched nonwoven. ▶ Bonding processes : Chemical bonding Thermal bonding Mechanical bonding ▶ Geotextiles have four major uses : Drainage Filtration Separation Reinforcement

Geotextile

17.4 Geotextiles ▶ Permittivity (통수성) (17.2) where P = permittivity ( ) hydraulic conductivity for cross-plane flow ( ) t = thickness of the geotextile, (Figure 17.4) ▶ Transmissivity (전수성) (17.3) where T = transmissivity ( ) hydraulic conductivity for in-plane flow ( ) (Figure 17.5)

17.4 Geotextiles

17.4 Geotextiles ▶ Hydraulic conductivity, Kn ▶ Permittivity, P: ▶ Hydraulic conductivity, Kp: - Nonwoven: - Woven: ▶ Transmissivity, T:

17.5 Geomembranes ▶ Geomembranes are impermeable liquid or vapor barriers made from continuous polymeric sheets that are flexible – thermoplastic (열가소성)or thermoset(열경화성) ▶ Hydraulic conductivity of geomembranes : ▶ Thickness of scrim-reinforced geomembranes :

Geomembrane

17.5 Geomembranes ▶ List of tests for geomembranes Density Mass per unit area Water vapor transmission capacity Tensile behavior Tear resistance Resistance to impact Puncture resistance Stress cracking Chemical resistance Ultraviolet light resistance Thermal properties Behavior of seams

17.5 Geomembranes

17.6 Geonets ▶ Geonets are formed by the continuous extrusion of polymeric ribs at acute angles to each other. ▶ The primary function of geonets is drainage ▶ Dimension of geonet : - witdth : 1.8 to 2.1m - length : 30 to 90m - aperture size : 30mm 30mm to 6mm 6mm - thickness : 3.8 to 7.6mm

Geogrid

Geonet

Geocomposite