Austin completes waste water tunnel

Engineering firm Parsons Corporation was awarded the contract to perform design and construction support services for the project, while the 6.3km tunnel was bored by contractor SAK Construction.

The DTT project is part of the city's greater plan to improve Austin's wastewater system and support sustainability. By reducing current flows in the existing interceptors, the tunnel will make wastewater collection capacity available for future downtown development and allows for greater building and population density, Parsons Corporation stated.

"From master planning, through design and to construction completion, we are proud to have worked with the City of Austin's Water Utility on this important infrastructure project," said Virginia Grebbien, Parsons group president. "Parsons applied innovative solutions to address subterranean, surface level, and urban issues in the design and throughout the construction phase of the project, including the use of polymer concrete for constructing the tunnel drop and access manholes and vortex hydraulic drop structures to address odour and corrosion issues."

The DTT was constructed with TBMs and includes 70ft (21m) deep access shafts - 30ft (9m) diameter - that were converted to tunnel access manholes. The tunnel is 20,000ft long (6096m), and it intercepts wastewater flows from main downtown interceptors at five locations with provisions for a sixth future location. The tunnel crosses under Lady Bird Lake three times and varies from 55 - 85ft (17m - 26m) below ground or lake surface.