Large-Diameter Tunnel Challenges during the Integrated Pipeline (IPL) Project: Fid-Bau Portal

Large-Diameter Tunnel Challenges during the Integrated Pipeline (IPL) Project

Shirk, Jonathan D.

Design of large diameter tunnel crossings of high traffic volume roads, railroads, and creeks or rivers requires incorporating standard tunnel design standards with multiple agency design standards, coordination with these agencies, and oftentimes requiring permitting or encroachment agreements. The design of several large diameter tunnels was required for the 150 mile integrated pipeline (IPL) project. The IPL Project is a water delivery system made possible through a partnership of the Tarrant Regional Water District and the City of Dallas. Each currently supplies water to over four million people in the Dallas Fort Worth area. IPL sections 12, 13, and 14 consist of approximately 30 miles of 108-inch pipe with a total of fourteen (14) tunnel crossings with a minimum tunnel outer diameter of 144 inches. One of the crossings is Interstate 35E which has a diameter of 168 inches. This paper will highlight the design requirements and the coordination involved for design and construction of these tunnel crossings. Each tunnel crossing was designed to meet minimum depth requirements and to minimize the tunnel shaft depths at either end of the tunnel. Settlement for each tunnel crossing was evaluated to determine appropriate tunnel diameter based on controlling agency loading requirements. Permit and operational requirements of the carrier pipe and tunnel also dictated several key design features, but the means and methods of construction were left up to the tunneling contractor. This paper will also summarize construction challenges and lessons learned during construction. Most tunnel crossings were less than 200 feet in length, but three crossings exceeded 600 feet in length. Lessons learned from the installation of a tunnel 600 feet in length led to design changes in the 805 feet Interstate 35E tunnel. All other tunnel crossings were designed with 144-inch diameter which only allowed for the carrier pipe to be welded to each pipe joint outside of the tunnel and pushed into place. Increasing the diameter of the Interstate 35E tunnel provides more flexibility for the contractor to address any issues during installation of the carrier pipe in the tunnel.