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SAK/Quest Completes Austin’s Downtown Wastewater Tunnel
Far beneath the surface of Austin’s Lady Bird Lake ‒ a 416-acre water reservoir that provides recreational opportunities as well as flood control ‒ years of intense “dirty work” took place, largely unnoticed by local citizens, as crews labored to create a huge wastewater tunnel that ran as deep as 80 feet underground.
The technological and safety challenges of excavating a four mile, downward-sloping tunnel along a path that runs parallel to a river and underneath a lake at three different locations were considerable. But the need for a gravity-powered wastewater system to accommodate Austin’s growing population well into the future was apparent to city of Austin planners. To tackle the job, the city brought in the joint venture team of SAK/Quest, consisting of St. Louis area-based SAK Construction and Quest Civil Constructors Inc. of Phoenix, along with Parsons Engineering. The tunnel, which was recently completed, is expected to last with minimal maintenance for at least a century ‒ twice as long as the antiquated system it replaced.
Construction on the $40 million tunnel began in early 2010. The project included approximately 20,554 linear feet of tunnel and utilized 121-inch and 84-inch diameter tunnel boring machines. In addition, SAK/Quest lined the tunnel with pipeline using the materials designed for long life and low maintenance. The Downtown Wastewater Tunnel is managed by the City of Austin Public Works Department.
Challenges to project team
How to perform deep excavation on the tunnel ‒ which closely parallels the Colorado River for much of its length as well as crossing underneath the lake ‒ was the major challenge for the SAK/Quest team. To allow tunnel construction access from five surface locations for the initial segment of the tunnel, SAK/Quest crews constructed four shafts to depths of 75 to 80 feet. In addition, the team set up bypass sewerage pumping to allow an existing lift station to be cleaned and converted into a fifth shaft.