Abstract
Rock falls and wedge failures are the predominant forms of slope movement along Interstate 77 between Canton, Ohio and Ripley, West Virginia. Plane failures, though present, are much less common. This portion of the highway passes through a number of rock cuts with near vertical benches. The rocks in these cuts are Pennsylvanian to Lower Permian in age and consist of alternating series of horizontally bedded, competent, well-jointed sandstone or limestone underlain by highly erodible shale. Because of its highly erodible nature, the shale is severely undercut in many places. This type of stratigraphy is highly conducive to rock falls and wedge failures.
Detailed line surveys were performed at nine selected sites to obtain structural geologic data regarding joint orientation, spacing, continuity, surface irregularities, nature of infilling material, and ground-water conditions. Stereographic projection techniques were used to analyze structural geologic data and identify kinematically possible modes of failure. The results indicate potential for numerous wedge failures along the Interstate. However, due to the steeply dipping nature of these wedges, they fail mostly where the shale below their lines of intersection has been undercut. Depending on their location on the slope and the extent of undercutting, many of these wedge failures are a combination of both sliding and fall and can be termed as “wedge falls.”
Laboratory tests were performed to determine densities, friction angles, and durability characteristics of rocks involved in failure. The results were used for quantitative analysis of wedge failures by the limiting equilibrium approach. Rock falls were evaluated only qualitatively. The study resulted in categorization of Interstate 77 into stable, unstable, and potentially unstable sections.
