Geotextiles types

The use of reinforcing geosynthetics in slopes is a commonly used technique in road embankment construction and can be used to stabilise slopes of bunds or dikes. The geotextile types used for soil reinforcement are woven high strength materials or geogrid type of materials. The design with these elements is outside the scope of this Manual. 

Composite geotextiles are formed by the integral combination of two geotextile types into a single (composite) geotextile material nonwoven plus nonwoven or woven plus nonwoven. The resulting composite stmcture exhibits the positive attributes of both component parts. Fig. 20.1(c) shows the stmcture of a woven—nonwoven composite geotextile. 

Geotextile type (tCOje/t) (tCOje/t) (tCOje/t) (tCOje/t)... 

Fig. 1. Schematic drawings of five types of geotextile fibers (a) monofilament, (b) multifilament, (c) staple fibers, (d) staple yam, and (e) sHt film.

Geotextiles may be woven, nonwoven, or knitted. AH types, woven, nonwoven, or knitted, are susceptible to degradation owing to the effects of ultraviolet light and water. Thus stabilizing agents are added to the base polymeric material to lessen the effects of exposure to ultraviolet light and water. 

Separation. In this function, the geotextile serves to separate two dissimilar materials (Fig. 3), eg, two different soils, landfill material and the native soil, stone material and subgrade sod, old and new pavement, foundation sods and various types of wads, or one of many other similar situations. In some instances, it is difficult to distinguish between the separation and stabilization functions because in both situations the geotextde is serving as a separator. However, in stabilization some additional phenomena occur. 

Moisture Barrier. When impregnated with an asphaltic emulsion, geotextiles become impermeable and can then be used as moisture barriers. The primary appHcation for this type of geotextile is in pavement rehabiHtation (Fig. 8). 

Soil Clay is the primary construction material for settling basins and waste treatment evaporation ponds. Since there is no single type of clay even within a given geographic area, the shrinkage, porosity absorption characteristics, and chemical resistance must be checked for each application. Geotextiles can be incorporated into basin and pond clay construction to improve the performance of the structure. 

In nonwoven geotextiles, the fibers are much thinner but far more numerous. The various types are needle-punched, resin-bond, and melt-bond. All contain a labyrinth of randomly oriented fibers that cross one another so that there is no direct line of flow. The fabric must have enough open space to allow liquid to pass through, while simultaneously retaining any upstream movement of particles. The needle-punched nonwoven type is very commonly used as a filter material. 

The second part of the geotextile filter design is determining the opening size necessary for retaining the upstream soil or particulates in the leachate. It is well established that the 95% opening size is related to the particles to be retained in the following type of relationship. 

In gas-collector systems, either a granular soil layer or a needle-punched nonwoven geotextile is placed directly beneath the LML or clay of a composite cap system. Gas compatibility and air transmissivity are the design factors that must be considered. Methane, the most predominant gas, should be compatible with most types of geotextiles including PET, PP, and PE. 

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