Keyholing and core farming: the perfect match Murv Morehead, Right-of-Way Coordinator, City of Overland Park, Kansas; Al Field, Owner, Al Field and Associates LLC, Phoenix, Arizona; members, APWA Utility and Public Right-of-Way Committee
tility repairs, which take place far too often in our public streets, are a fact of life. We can, however, minimize the detrimental effect they have on pavement. This can be accomplished by using the Keyhole, Coring and Reinstatement (KCR) process. KCR consists of core drilling through asphaltic or concrete pavement (core diameters of 6 inches to 24 inches are normally used); removing the pavement core/coupon and then using vacuum excavation to remove subgrade material until the utility in question is found. Following utility repair or other activity, the subgrade is replaced, usually with a ½-sack slurry, and the previously removed core/coupon is replaced into the core hole and secured with a bonding agent (the reinstatement step). While the KCR process has already yielded numerous benefits for various utilities and service providers, it provides other benefits to the municipality in which the process is used as well. The two most notable and noticed advantages, from the perspective of a municipal ROW Inspector/Coordinator, are:
Removed core 72 APWA Reporter
August 2012
Top hat street plate •
Reduction in impacts to the motoring public
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Reduction in excavation impacts
Benefit #1 – a reduction in impacts to the motoring public Prior to the advent of KCR, a typical excavation performed to locate and/ or repair a buried utility meant a minimum of three days of impact to traffic due to time required for setting up traffic control to saw-cut or jackhammer out the existing pavement, which is removed and hauled to a disposal or reclamation site; the activity within the exposed area takes place; backfill is placed; cold-mix is installed or a street plate is placed over the excavation; and traffic returns to normal, with
a temporary pavement patch to drive over for who knows how long. When the cold-mix temporary patch is replaced is anybody’s guess unless specified in the permit, but usually not until the number of permanent patches justifies ordering of a truckload of hot-mix, rental of a compactor and roller, another mobilization of traffic control and final restriping. The impacts manifest themselves in the form of cold-mix/ temporary pavement degradation, or lane closures during the day and the noise generated by vehicles driving over a street plate through the night. While KCR still requires a traveled lane closure, it rarely lasts more than one day with no further closures needed. If core holes need to be left open for an extended period of time (i.e., used to observe directional drill
