Construction Challenges with a Large Diameter Tunnel: Fid-Bau Portal

Construction Challenges with a Large Diameter Tunnel

Vazquez, Miguel / Biglen, Douglas / Haeckler, Christopher

The North Texas Municipal Water District (NTMWD) provides water and wastewater services to more than 1.7 million people. NTMWD is constructing the first new major reservoir in Texas in nearly 30 years. The 16,641-acre lake is located 40 mi northeast of the Dallas-Fort Worth (DFW) Metroplex. The project includes a new reservoir, 90-in. raw water pipeline, water treatment plant, and an 84-in. treated water pipeline. The 84-in. treated water pipeline will transport potable water from the treatment plant near Leonard approximately 24-mi to McKinney. The treated water pipeline crosses multiple creeks, rivers, highways, and wetlands. One unique aspect of the pipeline includes a 2,500 ft section that crosses a forested wetland, river, railroad, and FEMA floodway. Access challenges, cost, and constructability concerns influenced the design approach for this area. This paper will discuss the design process used in conjunction with the Construction Manager at Risk (CMAR) for the 2,500 ft, 60-ft deep tunnel including vertical shafts, soils conditions, carrier pipe installation, construction approach, and tunneling methods. The authors will discuss the construction process and challenges incurred during tunneling.