The Mill Creek/Peaks Branch/State Thomas Drainage Relief Tunnel (Mill Creek Tunnel) reached an important milestone on July 25, when the tunnel boring machine (TBM) broke through the shaft wall to complete the excavation phase. The large-diameter TBM, nicknamed “Big Tex,” completed a 5-mile journey that included 2 miles of 37.5-ft-dia excavation and 3 miles of 32.5-ft-dia excavation. Big Tex was the largest hard-rock TBM in operation in the U.S. during the excavation phase. The next phase will start with construction of the tunnel’s concrete liner. Once complete, the Mill Creek Tunnel will include 2 miles of 35-ft-dia tunnel and 3 miles of 30-ft-dia tunnel. Halff Associates led the design effort for this $320-million drainage relief project, including the centerpiece Mill Creek Tunnel, which is being constructed at depths reaching 170 ft underground. The project team includes the owner, City of Dallas, construction manager Black & Veatch and construction contractor Southland Mole JV. Pictured are members of Halff's Mill Creek Tunnel team on July 25 after the shaft wall excavation was completed.