11/15




Cumberland County, PennDOT District 8-0

AEG is the prime consultant for this project-specific open-end agreement and is providing alternatives analysis, preliminary engineering, final design, and construction consultation for a rock slope protection system located on SR 11/15 at the Cumberland/Perry County line. AEG is responsible for investigating the existing condition of the cut slopes, providing comprehensive analysis of rockfall geohazards, developing and recommending remediation measures, and completing preliminary and final design and construction oversight for the recommended measures. An analysis matrix was developed for the alternatives, such as scaling and vegetation removal, mesh draping with and without rock anchors, protective ditches and/or fencing, and rock cuts for both the north and south existing cuts. The matrix was based upon field observation, site photos, existing mapping, and published literature. The matrix analysis led to selection of the preferred alternate. Our analysis included: analyzing existing low altitude black and white and infrared aerial photography, performing detailed geologic mapping of cut slopes, producing digital photographs, preparing topographic base mapping of cut slopes, and performing Colorado Rockfall Simulation Program (CRSP) and RockPac III computer-based analysis of rock slopes. Key data include: structural geology and use of stereonets, determination of rock shear and compressive strength, and the occurrence of groundwater. Rock slope planar, wedge, circular, and toppling instability were assessed to identify potential mass failure zones. The combination of existing roadway alignment direction, stereonet analyses, rock quality, degree of weathering, and presence of groundwater were evaluated as a means to determine how the structural geology will influence the rock cut slope parameters. Care was taken to evaluate the orientation of rock wedges in order to prevent cut slope instability and potential failure.