Union Canal Tunnel
The oldest surviving transportation tunnel in the United States is the Union Canal Tunnel in Pennsylvania. At the time of the tunnel’s construction in 1826, it was considered an engineering marvel for this country. The historic significance of the tunnel was recognized in 1994 by being designated a National Historic Landmark. Originally 728 feet long, the construction of the tunnel required excavation through a ridge of mixed sedimentary rocks utilizing an early form of drill-and-blast excavation techniques. The interior of the tunnel was unlined with only the portals and approaches being lined with dressed stone masonry. The tunnel was later reduced in length to 620 feet as part of a canal enlarging project in 1858; and the canal and tunnel served as a primary transportation link until 1885.
Over time, the retaining walls of the approaches were overloaded due to an accumulation of debris, eventually causing a massive failure of one of the approach walls. Due the significance of the structure, all rehabilitation alternatives were required to maintain the architectural and historical integrity of the tunnel. Working on the Hickey Architects-led team, Lachel assessed the stability of the tunnel, portals, approaches, and the surrounding slopes. Lachel was specifically tasked with investigating the safety of the unlined tunnel for use by the public. Lachel mapped the tunnel walls documenting visible structural features. Additionally, Lachel designed a slope stabilization system for the approaches consisting of shotcrete and soil nails, and produced drawing details and specifications for implementation of the slope stabilization efforts. The overall rehabilitation program included brick and mortar restoration of the portals and approaches, complete reconstruction of the failed approach retaining walls, and slope stabilization.