<p><p><figure id='attachment_3513' style='max-width:794px' class='caption aligncenter'><img class="wp-image-3513 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing grading of the rock cap aggregate on a roadway." width="794" height="539" /><figcaption class='caption-text'> Grading of rock cap aggregate. From Uhlmeyer, J., L. Pierce, J. Lovejoy, M. Gribner, J. Mahoney, and G. Olson. Design and Construction of Rock Cap Roadways: Case Study in Northeast Washington State. In Transportation Research Record: Journal of the Transportation Research Board, No. 1821, Figure 5 (c), p. 45. Copyright, National Academy of Sciences, Washington, D.C., 2003. Reproduced with permission of the Transportation Research Board.</figcaption></figure><h2>Project Summary/Scope:</h2>Reconstruction of State Route 20 in Washington used a rock cap layer to solve frost heaving and thawing problems in pavement. There was a possibility that car tires might be punctured by the shape of the rocks used for the rock cap and that trucks hauling rock material might get stuck during dumping.</p><p>Subsurface Conditions: The base course consisted of crushed stone and a borrowed subbase layer. The crushed stone base contained silty gravel material approximately 60 mm thick. The subgrade contained silty sand with gravel and cobbles. The water table was shallow and the natural moisture content ranged from 3.3 to 12.0%.</p><p>The 660 mm thick pavement was designed to have an 80 MPa resilient modulus and 500,000 equivalent single-axle loads. The design service life was 20 years. The pavement system consisted of a hot-mix asphalt layer of 100 mm, a crushed stone base of 100 mm, and rock cap of 460 mm.</p><p>The rock material was placed over a subgrade using a belly dump truck, and then graded. This process continued until a 90 by 150 m area had a lift of 150 to 200 mm. Next, the rock cap was compacted and another lift was added to the previously compacted area. A crushed stone base was placed directly on top to confine the rock cap. A bituminous surface treatment was place on the crushed stone base before the final asphalt.</p><p><img class="aligncenter size-full wp-image-3515" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic representation of Rock cap overlaid with crushed stone sub-base. The rock cap was compacted and another lift was added to the previously compacted area. A crushed stone base was placed directly on top to confine the rock cap. A bituminous surface treatment was place on the crushed stone base before the final asphalt." width="607" height="562" /></p><p>&nbsp;</p><p><img class="aligncenter wp-image-3516 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing the placement of rock cap on a roadway using belly dump trucks." width="877" height="590" /><h2>Performance Monitoring:</h2>The measured subgrade resilient modulus values were 60 to 3,210 MPa. The FWD deflection measurements showed that the rock cap sections performed well during the period from May 1999 to April 2002. No maintenance was required and the road was in service for a whole year.<br><h2>Project Technical Paper:</h2>Uhlmeyer, J.S., Pierce, L.M., Lovejoy, J.S., Gribner, M.R., Mahoney, J. P., and Olson, G.D. (2003). “Design and Construction of Rock Cap Roadways: Case Study in Northeast Washington State.” Transportation Research Record, 1821, 39-46.<br><h2>Date Case History Prepared:</h2>November 2012</p></p>