- Pennsylvania Department of Conservation and Natural Resources
- Advanced Construction Techniques, Ltd.
- Somerset, Pennsylvania
- Our Role
- Tunnel Inspection, Evaluation, Repair, Structural, Grouting Design, Drainage Design.
- 3,300 feet long
- Construction Cost:
- $12 million
- 3 years
- The rehabilitated tunnel is a critical link in one of the nation’s longest and most scenic rail-trails, the Great Allegheny Passage
- The trail is revitalizing local economies, once dependent of the railroad, coal mining, and steel-making
- The trail provides a free recreational resource, free from motorized vehicles.
The 3,300-foot long Big Savage Mountain Tunnel was constructed in 1911 as part of the Western Maryland Railroad line. After providing continuous rail service, it was abandoned in 1975. For the next 25 years, failure in the crown and wall of the tunnel developed due to adverse geologic conditions, significant groundwater inflows into the tunnel, and repeated freeze-thaw cycles.
The tunnel was rehabilitated to provide a critical missing link in the Great Allegheny Passage, a 334-mile long cycling and hiking trail between Pittsburgh, Pennsylvania, and Washington, D.C.
The tunnel was unsafe and in need of extensive repairs to stabilize the failing crown and walls. Seepage into the tunnel, along with freeze-thaw, caused severe distress over significant portions of the structure. Replacement of the concrete portals was also required. Our firm provided an alternate design that included more than 6,000 rock bolts, in conjunction with fiber-reinforced shotcrete, to stabilize the existing concrete tunnel liner.
In addition, voids above the crown were back-grouted with lightweight cellufoam grout. Drainage was provided using a synthetic drainage mat covering the walls and crown, which drained to a sub-base drainage pipe system. The final liner consisted of a shotcrete liner covering the drainage mat layer. The Gannett Fleming team also designed the portals to match the original portals and maintain their historical appearance.
- More than 6,000 Swellex anchors installed in tunnel walls and crown
- Lightweight cellufoam grout to fill voids behind existing tunnel liner
- Geocomposite drainage mats installed in walls and crown
- Drainage mats connected to extensive subsurface drainage pipe system
- New liner constructed of steel fiber reinforced shotcrete
- Stabilization techniques integrated with original liner.
- Today, the Allegheny Passage is one of the most well-known rail-trails in the country, providing a spectacular recreational resource, as well as an economic asset for the surrounding towns.
- Award of Merit, 2007, Association of Conservation Engineers, 14th Annual Carl V. Anderson Conservation Project Engineering Awards Competition
- Diamond Award of Excellence, 2006, American Council of Engineering Companies of Pennsylvania, Engineering Excellence Awards.