Waller Creek Tunnel
Downtown Austin has suffered from severe flooding for years. When completed the Waller Creek Tunnel will provide flood relief for much of the downtown area. The tunnel will run upstream from its outlet at Lady Bird Lake along Waller Creek and will terminate at Waterloo Park. The primary geology along the alignment is Austin Chalk with Eagle Ford Shale present at both the upstream and downstream ends. The tunnels will be excavated using multiple roadheaders and will eventually receive a cast-in-place final concrete lining.
The sole shaft on the project is located at 4th Street, and is a 70-ft deep, 30-ft diameter work shaft, which will eventually become the 4th Street Inlet Structure. The main tunnel is a 5,200-ft long conveyance/storage tunnel comprised of three different cross-sectional diameters of 26.5 ft, 22.5 ft, and 20.5 ft respectively. In addition, two large span connection chambers are located at the 4th Street and 8th Street Inlet locations.
Lachel’s work on the project began during the bid phase, where we performed a complete project takeoff and check estimate in support of S.J. Louis Construction of Texas (SJL), who eventually won the bid for the project. The contractor-style check estimate was performed utilizing Heavy Bid software.
Following project award, Lachel designed the initial support for the work shaft and tail tunnel, the two connection chambers, and the three different diameters of conveyance/storage tunnel. During design, particular attention was paid to the arch capacity of the chalk in the large connection chamber spans, which were over 60 ft in length, and to the swell potential of the Eagle Ford Shale. The designs utilized both traditional empirical calculations and numerical analysis using Plaxis, and resulted in the development of four ground support categories for each diameter of tunnel. Lachel was also tasked to evaluate the merits of substituting poly propylene fibers for steel fibers for use in their shotcrete mix, and to evaluate substituting friction-anchored Omega bolts for traditionally grouted Dywidag rock dowels. In both cases, the submittals developed by Lachel provided analysis and supporting calculations which allowed the substitutions to be accepted by the Owner.