Old Neiffer Road Bridge Design

HISTORIC PRESERVATION OF A CLASSIC STONE ARCH BRIDGE IN MONTGOMERY COUNTY, PA.

Our Client’s Challenge

The Old Neiffer Road Bridge (also known as Sunrise Mill Bridge) is a historic bridge spanning Swamp Creek at Sunrise Mill in Schwenksville, Montgomery County, Pennsylvania. Originally constructed in 1845, the bridge is considered a contributing element to the National Register of Historic Places-listed Sunrise Mill complex, whose buildings date from 1767, including a dwelling, mill, and barn. Officials added the bridge to the National Historic Register in 1977.

The bridge is a four-span, closed spandrel, stone arch structure that carried the former Old Neiffer Road over Swamp Creek. The bridge is closed to vehicular traffic since the Pennsylvania Department of Transportation (PennDOT) constructed a new Neiffer Road Bridge south of the original bridge. Storm surge and age caused the asphalt-wearing surface to crack, allowing water infiltration that resulted in multiple full-depth holes in the stone arches and required old stone bridge preservation.

Our Solution

Our team provided engineering, environmental permitting, and construction consultation to save the historic structure as a pedestrian-only trail connector from the Sunrise Mill complex to the future Swamp Creek Trail.

Thoughtful bridge design and construction incorporated original character-defining features and maintained the historic bridge’s profile. Portions of the collapsed spandrel walls and arch rings required rebuilding using existing stones that had fallen into the creek, lessening the bridge’s environmental impact on the waterway.

Rehabilitating an arch bridge requires temporarily supporting the arches to dismantle and reconstruct them while preserving as much of the structure as possible. The bridge project included:

Cleaning and repointing the stone masonry.
Replacing the existing backfill with lightweight concrete fill.
Completing a full-depth bituminous pavement replacement over the bridge and the approaches.
Repointing broken mortar and repairing structural stone masonry.

Construction crews removed the asphalt pavement and filled the stone arch rings above the arches. Lightweight concrete filled the arch rings and the interior of the spandrel walls, helping stabilize the arches by locking in the stones and filling voids to prevent water from infiltrating the stone masonry.

Crews then applied an asphalt-wearing surface over the fill. Any cracked or missing stones in the piers, abutments, wing walls, spandrel walls, and arch rings required replacement with existing stone that had fallen into the creek or from a local quarry that matched the material in type and appearance.

Scour countermeasures included using riprap (Class R-6 rock) at the base of the piers and the southern downstream wing wall. The concrete-capped barriers now feature a wood railing system installed and anchored to the caps using brown powder-coated metal brackets.

The approaches had new wooden trail fencing installed, like the wood railing system installed at the bridge barrier. The railing system is a protective measure for trail users’ safety, which blends with the natural environment. The railing features 6-inch wood posts connected by 2-inch by 6-inch wood boards.

Key Features

Historic preservation of a stone arch bridge.
Creates a new pedestrian bridge connector to the proposed Swamp Creek Trail.
New grassy areas on approaches add open space for park patrons.
New railing system installed for cyclists’ and pedestrians’ safety.

Outcomes

Preserves a significant component of the historic Sunrise Mill complex.
Design and construction incorporate original character-defining features.
Conserves a prime example of a 19th-century stone arch bridge.
Arch bridge preservation contributes to Pennsylvania’s bridge preservation programs.