On November 10, 2009, a large rockslide struck U.S. Route 64 in the Ocoee Gorge in Polk County, Tennessee, following an intense rainfall event associated with tropical storm Ida. The slide obliterated the roadway and a sidewalk, blocked access to a boat ramp, and impacted area access as well as the local economy for five months. Approximately 15,000 cubic yards of rock, soil and forest vegetation buried the roadway to a height of nearly 25 feet. An adjacent historic concrete faced timber crib dam operated by the Tennessee Valley Authority (TVA) was not impacted by the slide. An initial smaller slide occurred early in the morning closing the roadway and mobilizing maintenance, repair and television crews to site. Observation of the slope during the initial cleanup indicated a larger slide mass was failing and provided sufficient warning to evacuate workers clearing the initial rock debris before the main slide fell, avoiding potential loss of life. Television news crews on site to cover the initial smaller slide obtained rare video footage of a major rockslide occurring. Originally called the Copper Road because it was constructed to haul ore west along the Ocoee River valley to Cleveland, Tennessee, U.S. Route 64 is a vital east-west two-lane highway providing the only principal access between extreme southeast Tennessee and adjacent North Carolina. Detour routes around the area extended travel up to two extra hours. The roadway follows the winding Ocoee River, the site of the Whitewater events of the 1996 Summer Olympic Games. The roadway is also the primary route for commuters from Polk County to jobs in neighboring Bradley and Hamilton Counties, a daily commute that ranged from one to two hours for citizens on the far side before the slide occurred. The river and roadway traverse the Cherokee National Forrest, providing access to outdoor enthusiasts. The roadway also serves as the primary route for emergency and commercial vehicles serving the towns, tourist camps and Whitewater rafting outfits in the area, and is also the main east-west corridor for commercial trucking from Chattanooga and southeast Tennessee with North Carolina. The rock slope, like many within the Ocoee Gorge, has been monitored closely by the Tennessee Department of Transportation (TDOT) under their rockfall hazard program. Area TDOT maintenance workers, well aware of the issues posed by many of the rock slopes within the gorge, check the slopes and roadway for changes regularly during the winter freeze-thaw events and after significant rainfall. The rocks in the Ocoee Gorge consist of late Precambrian, complexly folded, thin to medium bedded, low-grade metasediments, including slates, phyllites and metagraywackes. Differential weathering of thin beds of slate and phyllite bounded by more competent metagraywacke can lead to planar and wedge failure of steeply dipping beds, intersecting joints and cleavage planes. Exposure of these weak beds in the toe of the slope, in conjunction with over five inches of rain over a 24-hour period, led to planar sliding failure of a portion of the rock slope. Remediation included scaling of loose rock and soil; trim blasting of remaining beds on the slope to remove the potential for further rockfall; installation of pattern rock bolts throughout the slope; and installation of drains at the toe of the slope. Due to the proximity of the TVA dam, blasting vibrations had to be monitored. Limited access along the mountainous two-lane highway hampered rock slope mitigation construction.
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