<p><p><div></p><p><figure id='attachment_3437' style='max-width:440px' class='caption aligncenter'><img class="wp-image-3437 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Location map for temporary access road at Irwin Lake, Monroe, Louisiana" width="440" height="397" /><figcaption class='caption-text'> (© 2011 Google)</figcaption></figure></p><p></div><div><h2>Project Summary/Scope:</h2>The weir dam controlling the water level of Irwin Lake near Monroe, LA, had two blow-outs that threatened to wash out the dike and drain the lake. The U.S. Army Corps of Engineers, Vicksburg, MS, required a temporary access road, approximately one mile long, to haul riprap from the main road (LA 595) into the dam area. The road was required to support 300 trucks carrying approximately 25 tons of riprap each. Six inches of ballast-type stone had previously been placed over soft spots along the existing dirt road. The stone had completely disappeared into the clay due to punching shear failure of the subgrade under traffic loads.</p><p>Subsurface Conditions: The road was to be constructed over saturated gumbo clay, which had very low bearing capacity, particularly when wetted.</p><p>The design called for a six-inch base layer, reinforced with geogrid to reduce the amount of expensive aggregate required. The project required 39 rolls of geogrid, 164-feet long by 13-feet wide, to extend over the 6,000-foot length. A single-lane road was built since traffic volumes would be relatively light. To prevent the rock from spilling out of the truck over a much wider area than the road, trucks were required to drive onto the geogrid from the advancing roadway and dump several small piles as they moved forward.<br><h2>Alternate Technologies:</h2>The following alternatives were considered:<br><ul> <li>Build a thick road section to withstand heavy truck loads at considerable costs.</li> <li>Build a thin section but maintain the road during weir repair by keeping construction equipment mobilized to add and grade base fill as required. Furthermore, a tracked vehicle would be required on site to pull out trucks that would inevitably get stuck.</li> <li>Use lighter haul trucks but pay higher costs to haul riprap.</li></ul>Reinforce a thin road base with geogrids.</p><p></div><h2>Performance Monitoring:</h2><div>The weir repair began immediately after the completion of road construction. Although the road was originally designed to support about 300 trucks carrying riprap, the actual number of trucks required was on the order of 500. Nevertheless, the road held up to the additional traffic without any significant deterioration over the course of the five weeks.</div><div></div><h2>Date Case History Prepared:</h2><div><strong> </strong>November 2012</div></p></p>