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r :•Sac. 1.1 Basic Description of Geosynthetics <br />Thus the two-pronged thrust of this opening section is to establish the major <br />targets for which synthetic fabrics are aimed. This is to do the intended job better (e.g., <br />no deterioration of material) and to do it less expensively (i.e., either in initial cost or in <br />longer life and less maintenance). <br />I call the general area “geosynthetics," recognizing that the materials are used in <br />soil and are synthetic (usually made from hydrocarbons). The specific families of <br />geosynthetics on which we will focus are the following; <br />Geotextiles <br />Geogrids <br />Geomembranes <br />Geocomposites <br />which are shown for comparative purposes in Figure 1.1. <br />1.1.1 Geotextiles <br />Geotextiles form the largest group of geosynthetics that will be discussed in this book. <br />Their rise in growth during the past 10 years has been nothing short of awesome. They <br />are indeed textiles in a traditional sense, but consist of synthetic fibers rather than natu ­ <br />ral ones like cotton, wool, and silk. Thus biodegradation is not a problem. The fibers <br />are made into a flexible, porous fabric by standard weaving machinery or are matted <br />together in a random, or nonwoven. manner. Some are also knit. The major point is that <br />they are porous to water flow across their manufactured plane and also within their <br />plane, but to a widely varying degree. There are at least 80 specific application areas for <br />geotextiles tiiat have been developed; however, the fabric always performs at least one <br />of five discrete functions: <br />1. Separation <br />2. Reinforcement <br />3. Filtration <br />4. Drainage <br />5. Moisture barrier (when impregnated) <br />Geotextiles, with an orientation toward these functions, form the basis of Chapter 2. <br />1.1.2 Geogrids <br />Geogrids represent a small, but rapidly growing, segment of the geosynthetics area. <br />Rather than being a woven, nonwoven or knit textile (or even a textilelike) fabric, <br />geogrids are plastics formed into a very open netlike configuration. Often they are <br />stretched in one or two directions for improved physical properties. By themselves, <br />there are at least 25 application areas, and they function in two ways: <br />1. Separation (occasionally) <br />2. Reinforcement (usually) <br />Geogrids form the basis of Chapter 3. <br />• <br />’»-• <br />:s, <br />J <br />.a <br />1