Of the different modes of rock slope failures encountered along highways in the Appalachian Region of Tennessee, the wedge failure has become the most dangerous to the motoring public.
Nearly all of the wedge failures experienced by the Tennessee Department of Transportation have been located in eastern Tennessee both in the Ridge and Valley Province and the Blue Ridge Province. However, the majority of wedge failures experienced has been located in the mountainous topography of the Blue Ridge Province, particularly along Interstate 40 (1-40) in Cocke County.
Wedge failures along Tennessee highways are usually associated with hard, well indurated shale or slate lithologies which have well developed planes of weakness. Most of the wedge failures are associated with pre-Cambrian rock units, although some Cambrian, Ordovician and Mississippian units are also involved.
Rock slopes subject to wedge failures can be evaluated by steronet analysis techniques. These procedures are usually required for preventative and/or correction measures. The treatment of wedge failures in Tennessee involves both stabilization and protection methods. The concepts of drainage, removal, and restraint provide stabilization. Drainage methods involve de-watering with the use of horizontal drains. Removal concepts include mass grading operations, controlled blasting techniques and “toe” clean-out maintenance procedures. Restraint of rock wedges involves the use of buttressing concepts such as rock buttresses and concrete buttresses. Proposed, but yet untried in Tennessee, are buttressing concepts utilizing rock bolts.
Protection methods include wire meshing, catchment fences, berms, and walls.