Wedge failures in the Blue Ridge Province of East Tennessee : a case study of the Hartford area slides

Wedge failures are a complex and dangerous type of rock slide that have occurred often in road cuts in the Blue Ridge Province of eastern Tennessee. The stretch of Interstate 40 between Hartford, Tennessee and the North Carolina state line has experienced frequent wedge failures. These failures have led to disruption of traffic flow, expensive cleaning efforts, and extensive corrective measures. Previous studies have not critically examined the distinctive influence of meteorological events on wedge failures. This study incorporates methods used in those previous studies as well as the relationship precipitation and temperature have with wedge failures. A model has been developed from this study that can be use as a preliminary checklist for the investigation of other Southern Blue Ridge family wedge failures. Some of the methods used in this investigation were found to require special conditions and data that had not been noted before. The methods that needed special consideration include the use of the Schmidt hammer, the back-calculation of values with the program BACKPACK, and the use of the factor of safety equation. All these methods have valid uses and applications, but were of limited value in this investigation. The wedge failures near Hartford, Tennessee conform to the geometric dimensions, among other passive causes, determined to cause failure for other regions. The primary active cause of failure for the Hartford area slides is thought to be precipitation. The effects of precipitation, however are too complex, variable, and site specific to be expressed in simple cause and effect terms. Efforts to quantify the causes of wedge failures will help to clarify the conditions conducive to failure and therefore allow future road construction to avoid areas predisposed to failure.