MSE walls aide in tunnel reconstruction in Washington D.C.

Sept. 6, 2019

From 2016 until the fall of 2018, the Virginia Avenue Tunnel underwent improvements structurally and functionally. Originally built in the late 1800s, the tunnel has helped heavy freight railway traffic to pass through downtown Washington D.C. A major reason for the upgrade was to increase the height of the tunnel to accommodate double-stacked intermodal freight trains, which are now common throughout the industry. The new replacement tunnel was designed with two parallel concrete boxes.

At the eastern portal, where I-695 turns north/south near the Anacostia River, new retaining walls were required to build the embankment back up to the required grade of the street above the tunnel and serve as a headwall for the entrance.

The design-build joint venture of Clark and Parsons used mechanically stabilized earth (MSE) retaining walls.

One MSE wall serves as the face of the dual concrete tunnel, filling between the two tunnels, and extending north to the face of an existing MSE wall and cast-in-place wall. A benefit of the modular MSE wall system on this project was that it allowed for a simple method for filling in the roadway embankment in between the two concrete tunnels. The facing panels were easily designed prefabricated to fit in between the tunnels, as well as in between a tunnel and existing retaining wall.

The second MSE wall—on the south side of the tunnel entrance—serves as a wing wall parallel to the tracks. To protect pedestrians from the tracks below, the MSE wing wall included precast coping secured to the top panels with steel plates, to ensure that any load or impact applied to the anchored fence will not cause it to shift out of place.

Building the MSE walls in between the tunnels, and adjacent to existing structures required considerations for differential settlement between structures with different foundation types. Slip joint covers were used at three locations to ensure that any movement between different parts of the structures—during construction and service life—do not create localized separation or stress in the facing.

Both walls have a large ashlar stone finish and include two panels with a decorative CSX logo. A cast-in-place coping with guide rail was installed atop the face of the tunnel entrance.

The MSE wall system proved to be a simple and effective solution for filling the end of the new Virginia Avenue Tunnel, considering the geometric and geotechnical constraints.

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