<p><p><figure id='attachment_2590' style='max-width:807px' class='caption aligncenter'><img class="wp-image-2590" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing a drum roller compacting fill over a geogrid and geosynthetic placed in a roadway system." width="807" height="539" /><figcaption class='caption-text'> (Courtesy of National Highway Institute)</figcaption></figure></p><p><figure id='attachment_2591' style='max-width:810px' class='caption aligncenter'><img class="wp-image-2591" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of geosynthetic being placed in a roadway." width="810" height="608" /><figcaption class='caption-text'> (Courtesy of Kansas Department of Transportation)</figcaption></figure><h2>Basic Function:</h2>Geosynthetics (as reinforcement in pavement systems) are used to increase bearing capacity, reduce rutting, fatigue cracking, cracking due to heaving, and reflective racking.<br><h2>Advantages:<em> </em></h2><ul> <li>Relatively fast and easy placement</li> <li>Improvement of pavement performance</li> <li>Reduces the risk of subgrade support problems</li> <li>Prevents aggregate penetration of subgrade</li> <li>Geosynthetics are not significantly affected by moisture</li></ul><h2>General Description:</h2>Geosynthetics can be used in pavement systems between the subgrade and the base layer to improve and restrain the subgrade. They can be use within the base layer to increase the base stiffness. Design of the geosynthetic reinforcement is based on concepts of stiffened base course layers by confinement of geosynthetics. Methods are being adopted to use geosynthetics as base reinforcement to reduce the required base thickness and prolong pavement design life. A mechanistic-empirical design method, which incorporates the benefits of geosynthetics, is still being developed by AASHTO, FHWA, and the geosynthetic industry. Placement of the geosynthetic between the subgrade and base layers is relatively fast and easy and the benefits are immediate.<br><h2><strong>Geologic Applicability:</strong></h2><ul> <li>Applicable soil types of subgrades include silty sand, soft silt, clay with organic inclusions, silty clay, rounded sand, clay, and fine sand mixed with peat.</li> <li>Commonly used in subgrade with CBR less than 3. There is noticeable benefit when the subgrade has a CBR value of 3 to 8.</li> <li>Improves expansive soils when geosynthetic reinforcement is placed above the subgrade.</li></ul><h2>Construction Methods:</h2>The ground is prepared by removing stumps, boulders, and filling depressions. The Geosynthetic is rolled out overlapped as required and inspected for excessive damage such as holes rips and tears. The aggregate layer above the geosynthetic is back dumped and spread without driving directly on the geosynthetic. Compact the aggregate over the geosynthetic. See Holtz (2008) <em>Geosynthetic Design and Construction Guidelines</em> for more information.<br><h2>Additional Information:</h2>Current design methods of the geosynthetic reinforcement are empirical and semi-empirical. Very few states consider the use of geosynthetics for base reinforcement as standard practice but many are considering it on an experimental basis. Research is needed to demonstrate the life-cycle benefits of geosynthetics and to verify the results of physical model tests on long-term performance. Quality control during the installation of the geosynthetic layer is crucial to the performance.<br><h2>SHRP2 Applications:</h2><ul> <li>Stabilization of Pavement Working Platforms</li></ul><h2>Example Successful Applications:</h2><ul> <li>Evaluation of geogrid-reinforced granular base in an experimental project – Wyoming</li> <li>Base reinforcement with biaxial geogrid, long term performance – Georgia</li> <li>Field evaluation of geosynthetically-stabilized pavements – Virginia</li></ul><h2>Complementary Technologies:</h2>Geogrid reinforcement has been used with nonwoven geotextiles when subgrade is soft, or with geocomposites when drainage is needed.<br><h2>Alternate Technologies:</h2>Chemical stabilization of subgrades and base courses, excavation and replacement, use of high-quality base materials, additional aggregate with geosynthetic separator.<br><h2>Potential Disadvantages:</h2><ul> <li>Lack of an acceptable method to evaluate the difference between geosynthetic products</li> <li>Lack of a reliable AASHTO design method</li> <li>Lack of demonstration of life cycle cost benefits</li> <li>Not cost benefit in areas where base and subbase materials are inexpensive and of good material</li></ul><h2>Key References for this technology:</h2>Christopher, B.R., Berg, R.R., and Perkins, S.W. (2001). <em>Geosynthetic Reinforcements in Roadway Sections</em>. National Cooperative Highway Research Program, NCHRP Project 20-7, Task 112, FY2000, Transportation Research Board, Washington, D.C.</p><p>Berg, R.B., Christopher, B. R., and Perkins, S. (2000). <em>Geosynthetic Reinforcement of the Aggregate Base/Subbase Courses of Pavement Structures</em>, prepared for American Association of Highway and Transportation Officials Committee 4E, Prepared by the Geosynthetic Materials Association, 176 p.</p></p>