On August 14. 1989. the Kentucky Transportation Cabinet requested the Kentucky Transportation Center (KTC) to investigate an apparent drainage problem on the Western Kentucky Parkway. The area of concern was a rehabilitation project starting at Milepost 83 and ending at Milepost 90. The old PCC pavement was being broken and seated and was being overlayed with approximately five inches of asphaltic concrete. Longitudinal edge drains (Hydraway brand) were installed in 1988, but the PCC pavement was not broken until July, 1989. Two inches of asphaltic concrete base were placed over the old broken pavement, and were used as a driving surface for a short period. During that time, several heavy rains occurred. After the rains, it was evident that a large amount of silt had been "pumped " up through the two inches of new base and deposited on the shoulder. The source of water and the silt was not immediately evident.

Field inspection and laboratory permeability tests indicated the drains were performing, but on several occasions, more water was seeping through the new asphalt overlay and the old broken slab than the drains had capacity to carry. This was causing water to backup in the drains and flow upwards through the new overlay and exit onto the shoulder.

It is recommended that the outlet headwalls be spaced no farther than 450 apart on two percent grades or greater, and 200 to 250 feet apart on grades less than two percent. It is also recommended that riding surface be a Class I or a Class A surface mixture. This will reduce the amount of water that seeps into the pavement.

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The contents of this report reflect the views of the author who is responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, nor the Kentucky Transportation Cabinet. This report does not constitute a standard, specification, or regulation. The inclusion of manufacturer names and tradenames are for identification purposes only and are not to be considered as endorsements.