NPS Paw Paw Tunnel

The second-oldest surviving transportation tunnel in the U.S. is the Paw Paw Tunnel. Constructed between 1836 and 1850 as part of the Chesapeake and Ohio Canal, it runs 185 miles from Culpepper, Maryland, to Washington, DC. The project involved a geologic/geotechnical assessment, design, and field construction oversight for the stabilization of a 900-ft long rock slope on the canal near Paw Paw, West Virginia.

Schnabel conducted all field investigations, geologic mapping, pull-test on rock anchors, and all on-site field engineering during construction. Slope stabilization included scaling, rock dowels/bolts, pre-cast concrete shear keys, weep holes, and rockfall protective mesh. Our initial task was to create a topographic map of the rock slope in sufficient detail to conduct design and estimate project quantities. Using a drone that provided both a 3D point cloud and video, we performed an aerial survey of the slope and derived cross-sections and profiles.

A geologic reconnaissance was made of the slope that included characterization of the primary discontinuities. Kinematic analysis was conducted to model the planar failure mode of failure along the slope. Given the remote location of the project and the need to preserve the natural conditions within the National Park, we developed a bespoke stabilization plan that minimized the visual impact by using rock bolts and pre-cast concrete shear keys to stabilize the slope; a detailed scaling plan to remove loose and unstable rock from the slope; and a rock bolt anchorage testing plan as part of the design of the stabilization system.