Introduction:
The application of geosynthetics in civil engineering construction dates back to the 1970s. These are fabric-like materials made from polymers such as polyester, polyethylene, polypropylene, polyvinyl chloride (PVC), nylon, chlorinated polyethylene, etc. Their increasing use in civil engineering construction relates to concern for waste management and sustainability together with their amenability to recycling.
Geosynthetics is a broad term that incorporates geotextiles, geofoam, geopipes, geosynthetic clay liners, geomembranes, geonets, geogrids, and geocomposites that are made from synthetic materials (polymers or hydrocarbon chains). The function of geosynthetics can be summarized into five namely: separation, reinforcement, filtration, drainage, and moisture barrier.
Major Types of Geosynthetics
Geotextiles
Geotextiles are textiles whose fabric are made not from natural fabrics that have the capacity to decay easily but from petroleum products such as polyester, polyethylene, and polypropylene or from fiberglass. In preparation, they may be woven, knitted, or nonwoven and finally bonded using either chemical bonding (glue, rubber, latex, etc), thermal bonding (heating, melting, and bonding), or mechanical bonding (needle punching) depending on the purpose. Geotextiles are applied in erosion control works (drainage), filtration, and separation in soil especially in road construction works and reinforcement due to their tensile strength (see image below).
Geomembranes
These are impermeable liquid or vapor barriers made primarily from continuous polymeric sheets that are flexible. The type of polymeric material used for geomembranes may be thermoplastic or thermoset. Thermoplastic polymers include PVC, polyethylene, chlorinated polyethylene, and polyamide. The thermoset polymers include ethylene vinyl acetate, polychloroprene, and isoprene-isobutylene. The most important aspect of construction with geomembranes is the preparation of seams. Otherwise, the basic reason for using geomembranes as a liquid or vapor barrier will be defeated. Geomembrane sheets generally are seamed together in the factory to prepare larger sheets. These larger sheets are field seamed into their final position (see image below). There are several types of seams which may include:
- Lap Seam with Adhesive
- Lap Seam with Gum Tape
- Tongue-and-Groove Splice
- Extrusion Weld Lap Seam
- Fillet Weld Lap Seam
- Double Hot Air or Wedge Seam
Geonets
Geonets are formed by the continuous extrusion of polymeric ribs at acute angles to each other. They have large openings in a netlike configuration. The primary function of geonets is drainage. Most geonets currently available are made of medium-density and high-density polyethylene. They are available in rolls with widths of 1.8 to 2.1 m (≈ 6 to 7 ft) and lengths of 30 to 90 m (≈ 100 to 300 ft). The approximate aperture sizes vary from 30 mm x 30 mm (≈ 1.2 in. x 1.2 in.) to about 6 mm x 6 mm (≈ 0.25 in. x 2.5 in.). The thickness of geonets available commercially can vary from 3.8 to 7.6 mm (≈ 0.15 to 0.3 in.). Seaming of geonets is somewhat more difficult. For this purpose, staples, threaded loops, and wire sometimes are used (see the image below).
Geogrids
A geogrid is referred to as a geosynthetic material made of interconnected parallel sets of tensile ribs with perforations large enough to allow the surrounding soil, stone, or other geotechnical material to be struck through them. When used with appropriately sized aggregate fillings, geogrids offer reinforcement, stabilization, and even filtration. They are frequently utilized in civil engineering applications and are made from polymers like polyester, polypropylene, and polyethylene. Common types of geogrids are uniaxial, biaxial, triaxial and geogrid-geotextile composites. Each is designed and manufactured for specific construction applications with various geometric and structural index properties (see image below).
Geocomposites
Geocomposites are typically combinations of drainage (and sometimes barrier) material with two or more geosynthetic filter materials such as geotextiles, geogrids, geonets, and/or geomembranes. They are commonly used to prevent soil migration into the drainage system and also perform the entire function of geosynthetics which includes separation, reinforcement, filtration, drainage, and containment (see image below).
