6th Street Siphon at the Virginia Avenue Tunnel Reconstruction
The 6th Street Sewer Relocation and Siphon is an element of the Virginia Avenue Tunnel Reconstruction project in Washington, DC. This project is a design-build contract between CSX Transportation, Inc. and Clark/Parsons, a joint venture between Clark Construction and Parsons Transportation Group.
The project scope includes the replacement of an existing 4-foot brick and concrete combined public sewer operated by DC Water. The team also will replace a special drop manhole, which connects to a storm drainage system and a sanitary sewer as well as two break-in connections from the existing rail road tunnel drainage system.
The team will demolish the current sewer crossing to accommodate the reconstructed Virginia Avenue Tunnel and construct a three-pipe, inverted siphon. The new inverted siphon system consists of an upstream structure, one 8-inch ductile iron pipe encased in a 24-inch steel pipe to convey the dry weather (sanitary) flow, two 36-inch PVC pipes encased in 54-inch steel pipes to convey the combined sewer flow to a downstream structure. The piping system will function as inverted siphons with flow driven by a hydraulic head and a downstream structure. The encasement pipes were installed under the existing rail road tunnel by jack and bore method.
During the construction of the north and south siphon structures, Clark designed, installed, and maintained a by-pass system to mitigate any disruption to the existing combined sewer flow.