US Highway 421

Location: Harlan County, Kentucky

Geotechincal Consultant: Wayne Karem

Dr. Karem, while at another firm was retained by Brighton
Engineering Company of as the geotechnical engineering
consultant for a new highway located in southeastern
Kentucky in Harlan County. The alignment crosses through
rugged mountainous terrain with steeply sloping hillsides and
narrow, long valleys. The project is located just north of Cumberland Mountain and is affected by the regional overthrust fault system. The bedrock dips steeply to the north between 15 and 35 degrees on the eastern half of the alignment. The dip flattens to the west. This area has also been extensively deep and strip mined. Deep box cuts occur consistently through the new alignment. The exploration program was unique compared to typical KYTC projects and consisted of drilling 3 to 4 cores in each stability section to define the geologic section in the steeply dipping portion. Extensive measurement of strike and dip preceded drilling to help finalize the boring plan. Five drill rigs were used to complete the accelerated project schedule. The rigs included all-terrain, truck-mounted, and skid rigs.

Structural features such as joints and faults control the cut slope design. The rock dips steeply into the roadway along the south side of the alignment. Dr. Karem designed cut slopes to reduce the risk of rock fall into the roadway. Over 7000 linear feet of rock cores were collected and over 1000 Slake Durability tests were performed for this project.