Maryland SHA Sideling Hill
In the 1980s, a section of the Western Maryland mountains was blasted away to create room for Interstate 68. The cut through Sideling Hill consists of a pair of slopes that are 1,200 feet long and 360 feet tall. Differences in how the layered rock mass is weathering advanced to the point where rockfall posed a serious risk to the traveling public. Schnabel provided services to assess and help remediate this hazard.
The massive excavation to create the interstate revealed folded rock formations, creating the largest highway rock slopes in Maryland and one of the most iconic rock exposures in the Eastern U.S. Under a contract with Maryland’s State Highway Administration (SHA), we provided a rock slope hazard assessment and developed remediation concepts to identify risks and strategies to help SHA prioritize mitigation alternatives. To aid the decision process, we presented alternative rockfall hazard mitigation concepts and cost estimates, including various combinations of scaling, bench cleaning, vegetation removal, rockfall barriers, draped and/or anchored mesh, spot treatment with rock bolting, and shotcrete surface protection with drainage.
During the final design phase, we identified options for a flexible rockfall barrier. Among our recommendations were three fence height options based on a statistical analysis of rockfall modeling results; two conceptual design details that featured a flexible mesh and cabling system using proprietary rockfall fence materials and connections; and a rigid custom fence system involving additional steel posts and lateral cabling. We based our final design plans and specifications on the proprietary system, which proved to be the most cost effective for achieving SHA’s hazard reduction objectives.
As an innovative approach, we performed a high-resolution LiDAR survey to create a photorealistic, 3-D terrain model allowing rock structure mapping of otherwise inaccessible portions of the slopes and much more accurate hazard identification. We performed an overlapping LiDAR survey during final design for change detection analysis to assess weathering rates and identify specific high-risk rockfall source areas.