<p><p><figure id='attachment_1468' style='max-width:1014px' class='caption alignnone'><img class="wp-image-1468 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing an edge drain being placed along side a highway. The edge drain consists of a pipe inside a geosynthetic wrapping of granular materials." width="1014" height="677" /><figcaption class='caption-text'> Geotextile in pavement drainage. (Photograph courtesy of National Highway Institute).</figcaption></figure><h2>Basic Function:</h2>Geosynthetics improve pavement drainage by providing efficient drainage systems at different layers of the pavement, such as subgrade dewatering, road base drainage, and structure drainage systems.<br><h2>Advantages:<em> </em></h2><ul> <li>Rapid renewal of transportation facilities, minimal disruption of traffic</li> <li>Relatively fast and easy placement</li> <li>Enhance the system performance and life expectancy</li> <li>Prevent the saturation of underlying layers, and facilitate the lateral drain of water</li> <li>Improvement of drainage performance of pavement</li></ul><h2>General Description:</h2>Geosynthetics can be used under pavements or along edges of pavements to accelerate drainage of water away from the pavements. Geocomposite drainage layer is a successful alternative for pavement drainage systems as it quickly removes subsurface water from the pavement, provides a positive capillary break, and reduces damage from frost heave and subsequent thaw. Filtration is the core function in all drainage applications. Geotextile used as a soil filter should have a high percent open area with a controlled opening size to suit the soil being filtered. The geocomposite membranes are used as an effective water barrier component which protects underneath layers from water accumulation and moisture damage. Drainage capacity of subdrain or edge drain can be increased by wrapping the porous fill around the drain.<br><h2>Geologic Applicability:</h2><ul> <li>Geosynthetics are used for all types of soil to enhance drainage characteristics of pavements.</li></ul><h2>Construction Methods:</h2>The drainage geocomposite is placed in such a way that its roll width is perpendicular to the roadway centerline on the prepared subgrade. Aggregate subbase is end dumped onto the geocomposite and spread with a bulldozer and compacted with a smooth-drum vibratory roller to a density not less than 95 % of the maximum density. Compaction of the first lift above the geocomposite is done with a dozer initially and then with a smooth-drum roller with the vibrator turned off. Key installation issues affecting the performance of edge drain systems, such as maintaining the verticality of the drain panel (geotextile or geocomposite) in the trench, proper positioning of the drain panel within the trench, backfilling with open graded aggregate, timely installation of outlet fittings and pipes, and the use of outlet pipes with adequate pipe stiffness, should be taken into account.<br><h2>Additional Information:</h2>Drainage of water from the pavement system is important for the performance and service life of the pavements. AASHTO (1993) design guides consider drainage in the pavement design while the current AASHTO MEPDG assumes good to excellent drainage. Pavement drainage includes surface drainage, lowering of ground water, and internal drainage.<br><h2>SHRP2 Applications:</h2><ul> <li>Stabilization of Pavement Working Platforms</li></ul><h2>Example Successful Applications:</h2><ul> <li>Performance of Geocomposite Membrane As a Pavement Moisture Barrier, Virginia</li> <li>Field performance of Geosynthetic Highway Drainage System, Seventeen States of United State</li> <li> Instrumentation of Reinforcement, Separation and Drainage Geosynthetic test sections in the reconstruction of a highway in Maine, Maine</li></ul><h2>Complementary Technologies:</h2>Geotextile is often used with geonet or geomembrane to form geocomposite. Geotextile is also used with aggregate to form an edge drain system.<br><h2>Alternate Technologies:</h2>Granular drainage layers, Drainage pipes<br><h2>Potential Disadvantages:</h2><ul> <li>Limited test data for long-term performance</li> <li>Limited demonstration of life-cycle cost benefits.</li> <li>Geocomposite edge drains used in pavements are difficult to maintain</li> <li>AASHTO M-E design method does not consider the contribution of geosynthetic drainage.</li></ul><h2>Key References for This Technology:</h2>Christopher, B.R., Schwartz, C., and Boudreau, R. (2006). <em>Geotechnical Aspects of Pavements</em>. Report No. FHWA NHI-05-037. NHI, FHWA, U.S. Department of Transportation, Washington, D.C.</p><p>Christopher, B.R., Hayden, S.A., and Zhao, A. (2000). “Roadway base and subgrade geocomposite drainage layers.” <em>Testing and Performance of Geosynthetics in Subsurface Drainage, ASTM Special Publication 1390,</em> 35-51.</p><p>Koerner, G.R., Koerner, R.M., and Wilson-Fahmy, R.F. (1996). “Field performance of geosynthetic highway drainage systems.” <em>ASTM Special Technical Publication,</em> 165-181.</p></p>