During construction of the southbound lanes of I 65, Stations 120+00 to 218+00, in Hardin County, Kentucky, near Elizabethtown, large deformations were observed when dense-graded aggregate (DGA) base courses were loaded with construction traffic. Rutting and cracking of the DGA also was noticeable. A study was performed to determine the causes of the unstable subgrade and base, recommend remedial actions, and evaluate the effectiveness of the remedial measures. The stability, or bearing capacity, of the unstable pavement was determined for different construction stages and combinations of pavement layer thicknesses using a relatively new stability model HOPK-I. The stability of the pavement during early construction stages also was analyzed using Vesic’s bearing capacity equations; results were compared to those obtained from the ROPK-I stability model. Initially, a geotextile fabric had been placed on the clay subgrade in an attempt to stabilize the subgrade. Remedial action consisted of mixing the top 6 to 9 inches of DGA with 7 to 10 percent of portland cement. A 3-inch layer of DGA was placed between the cement-DGA mixture and asphaltic concrete to minimize reflective cracking. Remedial actions were analyzed using the HOPK-1 model and evaluated using the Road Rater. Based on stability analyses, the failure of the granular base was a result of a bearing capacity failure in the clay subgrade; the original design vas inadequate. Stability analyses and Road Rater results showed that the remedial action vastly improved the structural behavior of the pavement. Results indicate that the HOPK-I model may be a good analysis tool. The study also emphasizes the need to determine and analyze the constructability of pavement designs.

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