<p><p><figure id='attachment_2611' style='max-width:766px' class='caption aligncenter'><img class="wp-image-2611 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing the compaction of base material over a geogrid using a rubber tired roller." width="766" height="492" /><figcaption class='caption-text'> Compaction of base material on top of the geogrid. (Photograph courtesy of North Dakota DOT)</figcaption></figure><h2>Basic Function</h2>Mechanical Stabilization of subgrades and base courses is used to improve roadway support over soft, wet subgrade and improve performance of base course materials.<br><h2>Advantages:</h2><ul> <li>Increased supporting capacity of weak, fine grained subgrades</li> <li>Improved subsurface drainage and removal of moisture under pavement</li> <li>Reduced subgrade rutting in flexible pavements</li> <li>Frost protection</li> <li>Prevention of aggregate and subgrade intermixing by geotextiles</li></ul><h2>General Description:</h2>Mechanical stabilization improves roadway support over soft wet subgrades and improves performance of the base course materials by using a compacted gravel layer or granular layer in conjunction with non biodegradable reinforcements. Non-biodegradable reinforcements include wire mesh, fibers, geotextiles, geogrids, or geocomposites.<br><h2>Geologic Applicability:</h2><ul> <li>Applicable to weak subgrades, loose sand, and for stabilizing relatively thin aggregate base course layers on subgrades with CBR &lt; 8</li> <li>Mechanical stabilization with geosynthetics is applicable under the condition that the subgrade soils have low undrained shear strength.</li> <li>Geosynthetics are applicable to stabilize saturated subgrade material on a site having a higher water table.</li></ul><h2>Construction Methods:</h2>A thick granular layer is constructed to provide a working platform. Construction of this granular layer can cause disturbance in the subgrade. Blending gravel and recycled pavement material with poorer quality soils can provide a mechanically stabilized working platform. If the saturation condition returns the gravel blend can take on the same poorer support characteristics of the subgrade. Geogrids and geotextiles can be used in combination with a quality aggregate to minimize disturbance and allow construction equipment access to sites where the construction equipment cannot be supported by the poor soil. Geogrids and<br>geotextiles allow compaction of initial lifts on sites where the compaction equipment can be difficult or impossible. Geotextiles and geogrids reduce the extent of stress on the subgrade and prevent base aggregate from penetrating the subgrade, and reduce the thickness of the aggregate required to stabilize the subgrade. Rehabilitation of the pavement should only include maintenance of surface pavement layers.<br><h2>Additional Information:</h2>The thick granular layer can avoid or reduce frost problems by protecting the underlying subgrade layers. The granular layer also improves drainage of surface infiltration water, provides weight to reduce heave, and makes the system more uniform. Using geotextiles can increase the strength of the subgrade over time. A trial installation can be completed to determine if the aggregate damages the geosynthetic during installation.<br><h2>SHRP2 Applications:</h2><ul> <li>Embankment and roadway construction over unstable soils</li> <li>Roadway and embankment widening</li> <li>Stabilization of pavement working platforms</li></ul><h2>Example Successful Applications:</h2><ul> <li>Intersection of Route 575 and 616 – VA</li> <li>Section A-10 of Interstate 70 – PA</li> <li>US Highway 52 – ND</li></ul><h2>Complementary Technologies:</h2>This technology can be used with excavation and replacement or chemical stabilization.<br><h2>Alternate Technologies:</h2>Excavation and replacement, vibratory compaction, dynamic compaction, stabilization with dewatering, and chemical stabilization.<br><h2>Potential Disadvantages:</h2><ul> <li>Benefits of the use of geosynthetics in subgrade are difficult to quantify.</li></ul><h2>Key References for this Fact Sheet:</h2>Holtz, R.D., Christopher, B.R. and Berg, R.R. (2008). “Geosynthetic Design and Construction Guidelines.” FHWANHI-07-092, National Highway Administration, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C.</p><p>Maxwell, S., Kim, W., Edil, T.B. and Benson, C.H. (2005). “Effectiveness of geosynthetics in stabilizing soft subgrades.” Rep. No. 2292-45-15, Department of Civil and Environmental Engineering, University of Wisconsin-Madison,WI.</p></p>