Page 363 - Materials Chemistry, Second Edition

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334 Waste Management Practices: Municipal, Hazardous, and Industrial
Geotextiles (Figure 10.23b) are manufactured from synthetic polymers such as polypropylene,
polyester polyethylene, and nylon. Approximately 75% of all geotextiles are made of polypropylene
resin, 20% are polyester, and the remainder are nylon (U.S. EPA, 1993c; Oweis and Khera, 1998). The
polymers are formed into fibers and then into a woven or nonwoven fabric. When placed in the ground
these fabrics are termed geotextiles. They are porous to liquid flow across their planes and also within
their thickness, but to widely varying degrees. There are at least 100 specific application areas for geo-
textiles; however, they always perform at least one of five discrete functions (Koerner, 1998):

● Separation
● Reinforcement
● Filtration
● Drainage
● Containment (barrier, when impregnated)

Since geotextiles are composed of synthetic fibers rather than natural ones such as cotton, wool,
or silk, biodegradation is not a concern.
Geogrids (Figure 10.23c) are designed to function as reinforcement materials. Koerner (1998)
defines a geogrid as:

a geosynthetic material consisting of connected parallel sets of tensile ribs with apertures of sufficient
size to allow strike-through of surrounding soil, stone, or other geotechnical material.
Geogrids are plastics formed into a very open, grid-like configuration. Geogrids contain large
open spaces called apertures, which are typically 10 to 100 mm between the ribs. The ribs them-
selves can be manufactured from a number of different materials. The primary function of geogrids
is reinforcement. There are many application areas.
Geosynthetic clay liners (Figure 10.23d) are used as a composite component beneath a
geomembrane or by themselves in environmental and containment applications as well as in trans-
portation, geotechnical, and hydraulic applications (Koerner, 1998).
Geocomposites consist of various combinations of geotextiles, geogrids, geonets, geomem-
branes, and other materials. The major functions embrace the entire range of functions listed above
for geosynthetics: separation, reinforcement, filtration, drainage, and containment. The general
reason for the existence of geocomposites is the higher performance attained by combining the
characteristics of two or more materials.
Geomembranes are discussed earlier in this chapter and shown in Figure 10.4. The materials
themselves are ‘impervious’ polymeric materials used primarily for linings and for covers of liquid
or solid storage facilities. Thus, the primary function in containment is as a liquid or vapor barrier.
The range of applications, however, is broad. According to ASTM D4439, a geomembrane is
defined as

A very low permeability synthetic membrane liner or barrier used with any geotechnical engineering
related material so as to control fluid migration in a himan-made project, structure, or system.

Geomembranes are manufactured from continuous polymeric sheets, but they can also be made
from the impregnation of geotextiles with asphalt or elastomer sprays or as multilayered bitumen
geocomposites (Koerner, 1998).

10.4.25 COLLECTION LATERALS
According to the U.S. EPA (1994), the regulatory limit of a 30 cm maximum liquid head above the
liner cannot be achieved using an area collector alone; therefore, collection laterals are needed.
Collection laterals are perforated pipes that direct leachate to sumps for removal. During landfill