Cross-Town Tunnel Rehabilitation

The cast-in-place, concrete-lined Cross-Town Tunnel delivers drinking water from the Dalecarlia Water Treatment Plant to the northwest urban part of Washington DC. In December 2008, leakage from the tunnel was detected along a major parkway. Jacobs Associates was contracted by the District of Columbia Water and Sewer Authority to investigate the causes of the leakage and to act as prime consultant for design of rehabilitation measures. Investigation included a physical inspection of the 13,000-foot-long (3,963 m), 7-foot (2.1 m) internal diameter (ID) tunnel.

Prior to accessing the tunnel for rehabilitation, preparatory work included installation of a second isolation valve to comply with safety requirements for double isolation of tunnel facilities, and complete dewatering of the tunnel. In lieu of constructing a completely new vault for the second isolation valve, the design team developed a scheme to modify the existing valve vault and fit the approximately 19-foot-tall (5.8 m) gate valve used to shut off the flow to the tunnel. Once isolated, tunnel dewatering was accomplished using a submersible pump, with treatment occurring prior to discharge.

As the prime consultant, Jacobs Associates has been providing engineering support services for the construction of the Cross-Town Tunnel Rehabilitation Project. Approximately 800 feet (244 m) of steel pipes will be installed to control the leakage from the tunnel. To gain access to the tunnel, an existing, 26-foot-diameter (7.9 m) concrete shaft will be demolished to a depth of approximately 120 feet (37 m). This challenging construction work is being performed in an urban area with tight environmental constraints.
Jacobs Associates also provided construction schedule and cost estimating, and managed subconsultants for site civil designs, traffic control planning, permitting, geotechnical investigation, isolation valve and vault structural modification designs, noise and vibration controls, and corrosion protection design.