Austin Clean Water Program
The Austin Clean Water Program (ACWP) was created in 2001 to comply with the U.S. Environmental Protection Agency’s order to eliminate sanitary sewer overflows from the City’s wastewater interceptor system. Many of the projects administered by the ACWP contain tunnel sections, and three of the most significant include the Barton Creek Lift Station Relief Tunnel, the Shoal Creek 29th to 34th Street Tunnel, and the Little Walnut South Tunnel. For each of these projects, Lachel provided construction management services including resident engineering and inspection, contract administration and contractor submittal review. Project details were as follows:
The Barton Creek Lift Station Relief Tunnels, Section 1 and 2 were constructed utilizing mechanical excavation methods. Section 1 consisted of 1,700 ft of 91-inch excavated diameter tunnel driven through Colorado River Terrace alluvial material using a digger shield with ribs and boards for support. Section 2 consisted of 1,530 ft of 97-inch excavated diameter tunnel driven through the Del Rio (clay) and Georgetown (limestone) formations using a shielded TBM with ribs and boards for support. Both tunnels were pipe-in-tunnel completions with 33-inch diameter FRPM (Hobas) pipe. The project also included excavation of two deep shafts to depths of 75 and 78 ft respectively, in order to provide for construction of a temporary lift station and a vortex drop structure.
The Shoal Creek Tunnel project consisted of approximately 3,400 ft of 102-inch excavated diameter tunnel driven through the Del Rio and Georgetown formations with a Lovat TBM and supported using ribs and boards. The pipe-in-tunnel section was completed with 66-inch diameter FRPM (Hobas) pipe and cellular concrete backfill. The project included associated shaft construction for vortex drop structures and system tie-in work. The 29th Street shaft was roadheader excavation and utilized steel ribs and liner plate for support.
The Little Walnut South Tunnel project consisted of roughly 9,600 ft of 101-inch excavated diameter tunnel driven through the Taylor (claystone) and Austin (limestone) formations using a Dosco shielded TBM. It also included a separate interstate highway crossing and 540 ft of 108-inch tunnel excavated using a main beam TBM. The two tunnel segments were completed with 48-inch and 60-inch FRPM (Hobas) pipe and cellular concrete backfill. The work also included associated shaft construction and tie-in work.