Collapse threat prompts DC Water to reinforce 140-year-old tunnel with shotcrete, geopolymer
Washington D.C. (UI) — DC Water has completed extensive repairs on a 140-year-old section of the Northwest Boundary Trunk Sewer beneath 22nd Street NW, wrapping up the second and final phase of construction ahead of schedule and under budget.
The nine-foot diameter brick tunnel, built in the 1800s, was found to be at risk of collapse after a 2023 inspection revealed a void above the structure measuring 13 feet long by 10 feet wide. The discovery led to the emergency closure of a portion of 22nd Street and prompted a months-long, two-phase repair project.
The initial phase, launched in July 2024, focused on stabilizing the soil around the void and reinforcing the tunnel. A second phase was added after inspections revealed further damage both upstream and downstream, including longitudinal cracks, missing bricks and cobblestones, and tree root intrusion.
Crews worked around the clock, often two stories below ground, while the tunnel remained in active use carrying combined stormwater and sewage. Periods of heavy rain occasionally halted work as the system became overwhelmed.
The complex repairs included stabilizing the soil through grout injection, installing rebar frames, and lining the interior tunnel walls with four to nine inches of spray-applied shotcrete and geopolymer. Materials used included:
- 139,000 linear feet of rebar
- 25,450 rebar anchors
- 28 tons of shotcrete
- 459 tons of geopolymer
In total, more than 1,200 linear feet of the tunnel was rehabilitated. Northbound lanes on 22nd Street have reopened, and southbound lanes are expected to reopen before the evening commute. Demobilization of the work zone near 22nd and Q streets is currently underway.
DC Water coordinated closely with the District Department of Transportation to manage traffic disruptions during the project and thanked the public for its patience.
“DC Water operates approximately 2,000 miles of combined, separate, and stormwater sewers. Addressing aging water and sewer infrastructure throughout the District is a critical part of the 10-year, $9.6 billion Capital Improvement Program,” the utility said in a statement. “This includes replacing or rehabilitating similar large-diameter sewer lines that have reached the end of their useful life.”
Related News
From Archive
- NTSB publishes preliminary report on fatal gas pipeline explosion in Lexington, Mo.
- 290-mile gas pipeline expansion proposed across Georgia, Alabama and South Carolina
- Ripple Fiber breaks ground on $140 million project, expanding into central Mass.
- Centuri awarded nearly $400 million for U.S. gas infrastructure work
- Water losses cost U.S. utilities $6.4 billion annually, new report says
- Gehl and Mustang offer world’s largest skid loader
- Growing Pains and Gains
- Maryland lawmakers push to curb BGE pipeline spending, citing safety and cost concerns
- Authorities investigating trench collapse that killed worker in Ashburn, Va.
- City of Albuquerque halts fiber optic construction in response to damage, complaints
Comments