Design, Construction and Materials Illinois Department of Transportation PTA-D6 (Eff. 03/1998, Rev. 02/2005) Bureau of Materials and Physical Research

PAVEMENT TECHNOLOGY ADVISORY - GEOSYNTHETICS - PTA-D6

WHAT ARE GEOSYNTHETICS? drains. Wick (strip) drains, used to expedite drainage of deep, compressible The term “geosynthetics” refers to all deposits, have also been included in fabricated synthetic (usually polymeric) the geocomposite category. The core materials used in various geotechnical material could be HDPE, polypropylene, applications such as drainage, reinforce- polyvinyl chloride (PVC), high impact ment, , and lightweight fill. polystyrene, or a combination of two There are many potential uses for polymers. geosynthetics in highway projects. This document describes various geosynthetic refers to low-density cellular materials that are potentially useful in foam, either molded expanded highway construction applications. polystyrene blocks or extruded polystyrene sheets. Geofoam is used as GEOSYNTHETIC TYPES AND a super lightweight fill, with 1.5 to 3.0 APPLICATIONS pounds per cubic foot (pcf) density, compared to other lightweight materials The following is an alphabetical list of with densities ranging from 50 to 70 pcf. various geosynthetic types and some Geofoam's light weight makes it a viable potential uses of each: option for repair, and for Geocells are designed to protect slopes embankments on soft, compressible against erosion, stabilize steep slope deposits. Geofoam is also used for surfaces, provide protective linings for thermal insulation of pavements and channels, support heavy construction foundations. Geofoam, however, requires traffic on weak , and special design considerations with regards provide multi-layered earth-retaining to buoyancy, fungus attack, and the structures. Geocells are typically con- presence of petroleum products (asphalt, structed of high-density oil, or gasoline). (HDPE). The cells in the three- are used for soil reinforcements dimensional panels are opened and filled in embankments and walls, subgrade with granular material, which adds weight stabilization, and base to make the multi-layer system act as a reinforcement. Geogrids are charac- gravity . terized by integrally connected elements, Geocomposites are designed to replace with in-plane apertures (openings) aggregate and/or perforated pipe uniformly distributed between the subsurface drainage systems. A geo- elements. The apertures allow the soil to composite consists of a deformed, fill the space between the elements, perforated, or slotted plastic core and a thereby increasing soil interaction with the (filter) fabric wrap. Geocom- and ensuring unrestricted vertical posites include geonets, pavement edge drainage. The geogrids vary in drains (drainage mats), and sheet (wall) manufacturing process, polymer type, PTA-D6 (Eff. 03/1998, Rev. 02/2005) Page 2 coating, density, aperture dimensions, and The IDOT Standard Specifications for tensile strength and modulus. Depending and Bridge Construction addresses on the brand name and material, the several including: Fabric geogrid could be made of polypropylene, Envelope for Pipe Underdrains; Geotextile , polyethylene, or fiberglass. The Fabric, for ground stabilization and material coating, if needed, could be PVC, filter fence; Filter Fabric For Use With polyester, bitumen, elastomeric polymer, ; Fabric For Fabric Formed or latex. Concrete Revetment Mats; Geotechnical Fabric For French Drains; and Fiber Mat, serve as hydraulic for ditch lining. Additionally, the Standard barriers. Geonets are horizontal drainage Specifications address Geocomposite mats, often used in conjunction with Wall Drains and Drainage Mat geomembranes in applications. Underdrains. Acceptance of geosynthetic Geomembranes and geonets have materials is primarily based on limited uses for highway projects. They manufacturer’s certification. Some geo- are mostly used for containment of spills, synthetic materials and manufacturers leaking under-ground storage tanks, or have not been approved for a variety of other hazardous materials within the right- reasons. of-way. If use of a geosynthetic material is Geotextiles typically provide one of the warranted, and it is not covered by the following functions: separation/filtration; Standard Specifications, a Special reinforcement; drainage; or hydraulic Provision must be developed to specify barrier. They can be classified as woven, material properties, transportation, nonwoven, or knitted. Woven fabrics storage, construction installation method, exhibit high tensile strength, high and any required short-term or long-term modulus, and low strains, while nonwoven protection. fabrics have high permeability and high strain characteristics. Geotextiles are Note: The State Geotechnical Engineer manufactured in a variety of geometric should be contacted for current geo- and polymeric compositions to meet a synthetic practice and for review of number of different applications. Many district special provisions to ensure geotextiles are made of polypropylene. uniform statewide practice. Fabric formed concrete revetment mats, silt filter fences, erosion control blankets, ADDITIONAL INFORMATION and fabric envelopes for pipe or mat underdrains are examples of common IDOT is working to update and expand its geotextile applications. Geotechnical Manual, which contains a A geotextile's long-term performance is a discussion on geosynthetics. An Order function of the durability and creep Form for those who wish to purchase the characteristics of the polymer structure. Geotechnical Manual is available in the The effects of ground, weather, sunlight, “Doing Business” section of the IDOT and aging conditions must be considered website at www.dot.il.gov. when specifying a geotextile for a permanent application. If you have any questions, or for more information, please contact: USAGE BY IDOT State Geotechnical Engineer The uses and types of geosynthetics are Bureau of Bridges and Structures expanding rapidly. Some of the above- 2300 S. Dirksen Parkway mentioned geosynthetic types are used by Springfield, IL 62764 the Illinois Department of Transportation 217/782-7773 (IDOT) in various applications.