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Onion Creek Wastewater Interceptor

In an effort to relieve aging wastewater infrastructure and eliminate sewage overflows into the surrounding waterways, the City of Austin is constructing a 42-inch wastewater pipeline that will serve as a key element of the planned wastewater infrastructure upgrades for the burgeoning southeast area of Austin.

The Onion Creek South project consists of approximately 7,520 lf of 88-in excavated diameter tunnel, three shafts ranging in depth from 55 to 75 ft deep, and a short 30-ft long stub tunnel connecting this project to the adjacent Onion Creek North project.  At depth, the tunnels will be constructed in the Austin Formation, a soft limestone.  The running tunnel will be excavated using a main beam TBM, and the short connector tunnel will be excavated using a roadheader.

Lachel was retained by the contractor to provide tunnel engineering services throughout the construction of the project.  Work has included developing initial ground support designs for the TBM access shaft, the TBM running tunnel and horseshoe-shaped TBM starter and tail tunnels, and the horseshoe-shaped stub tunnel.  To date, rock conditions different than expected have been encountered, and Lachel has worked with the contractor in the field to modify the design to address the variable rock conditions