Wilmington Rail Viaduct - Physical Description

Physical Description

The viaduct extends from Vandever Avenue, on its east end (a location on the railroad known as LANDLITH interlocking), across the Brandywine Creek and then roughly parallel to the Christina River through Wilmington Station. The west end of the viaduct is adjacent to the Alban Park neighborhood of Wilmington, an area also known as West Yard.

The bulk of the viaduct, from Vandever Avenue to Lower Linden Street, consists of earthen fill (derived from the construction excavation for the viaduct) held between heavy ashlar sandstone retaining walls resting on concrete foundations. Some of the northern sections of the viaduct have fill enclosed in timber cribbing on one side of the right-of-way, but generally the fill is contained with retaining walls on both sides. The ashlar also forms the abutments for the overpasses carrying the railroad tracks across city streets, which are steel plate through girder or deck girder bridges. The fill carries three tracks for much of its length; sidings, some now abandoned, descend to street level by ramps at various points. It was topped with 4 feet (1.2 m) of ballast before tracks were laid.

The west end of the viaduct, below Lower Linden Street, was constructed as an arched viaduct when the underlying soil was found to be too soft to support the fill carrying the remainder of the line. Originally designed in stone, shortages of sandstone led to the construction of the 41-foot (12 m) arches in brick, instead. Twelve arches carry the line from Lower Linden Street to the (stone) Beech Street underpass, and twenty arches continue southwest from Beech Street to the former Baltimore and Ohio and Wilmington and Northern underpass. The remainder of the structure to its West Yard end is again of retaining wall and fill construction.

The bridge over the Brandywine Creek near the east end of the viaduct had to be replaced to accommodate the newly elevated track level. At the time, this part of the Brandywine was considered navigable water, though rarely used, and the railroad had to construct a moveable bridge to accommodate navigation. The railroad chose to use a swing bridge, and began construction of the center pivot pier in the winter of 1903. The first caisson sunk there was damaged by ice and swept away in a flood. A new caisson was built resumed after the winter passed and a stone-faced concrete pier, 35 feet (11 m) in diameter, successfully constructed. A second pier was built in the stream to the southwest, leaving two 59-foot (18 m) channels between the pivot pier and the bank and the pivot and second piers. Icebreakers were built on either side of the pivot pier. (The tidal nature of the Brandywine required them to be bidirectional.)

The superstructure of the bridge was manufactured by the Phoenix Bridge Company. It consisted of a 78-foot (24 m) plate girder from the southwest bank to a fixed pier, and a 158-foot (48 m) fishbelly girder from that pier to the northeast bank, turning on the pivot pier. It carries three tracks. Two buildings were erected on the bridge, one for a watchman and the signal levers that protected and operated the bridge, and one to house the gasoline engine that turned it. The interlocking levers on the swing bridge were placed in service on March 4, 1906; this was the first electro-mechanical interlocking using small levers (rather than the rod-linked armstrong levers typical at the time) on the Pennsylvania Railroad system.

The structure has undergone relatively little modification since its construction. A 1920s electrification program to Wilmington added support structures to string catenary wires along the length of the viaduct. During the early 20th century, the swing bridge over the Brandywine was fixed in place and the engine and control buildings removed. In 1955, the construction of the Walnut Street Bridge required an undergrade bridge to be built to carry a new, wider alignment of Walnut Street slightly to the east of its original course. The new bridge is of plate girder construction over concrete abutments and piers. In 1983, Amtrak replaced the superstructure of the Poplar Street bridge and refurbished the piers and abutments.