Hanging Lake and Reverse Curve Tunnels; I-70 Glenwood Canyon, Colorado, USA
Tasks Performed: Consultant responsible for conducting the feasibility study and preliminary design of the Hanging Lake Twin Tunnels and the Single Bore Reverse Curve Tunnel of the final segment of Interstate Highway 70 in Glenwood Canyon, CO. The work consisted of detailed surface geological mapping of several proposed alignments, including preparation of geological maps and cross-sections, fracture mapping and rock mass characterization, rock testing, determination of support requirements, and the development of preliminary designs and construction cost estimates for all tunnels. Preparation of comprehensive report.
In his recent publication “BUILDING I-70,” Dick Prosence, P. E., former District Engineer of CDOT (2003) writes: “Construction activities from 1981 until the dedication of the completed segment on October 8, 1992, could be the subject of an additional book. Incredibly difficult construction problems were faced and solved. Hanging Lake and Reverse Curve Tunnels were completed almost routinely due in large part to intensive geological investigation and analysis completed by Horst Ueblacker and supplemented later by Woodward Clyde.”
The detailed geological investigations, rock mechanics studies, and cost analyses performed during the preliminary design phase of this project have greatly reduced the risks of encountering changed conditions during construction of the tunnels which are frequently the cause of delays and cost overruns on the contracts, and litigation. The tunnels were completed ahead of schedule and below budget for a total cost of $75 million.
Duration: 1978-1979 (8 months)
Description: The Hanging Lake Tunnels (maximum length 1,115 meters), located approximately 80 kilometers west of Vail, Colorado, constructed between 1989 and 1991, represent the final link of Interstate Highway 70 completed. These four tunnels, along with the 191 meter-long Reverse Curve Tunnel (all located in Glenwood Canyon), are owned and operated by the Colorado Department of Transportation (CDOT). These tunnels were the first federally funded highway tunnels to implement the reinforced rock arch concept of the New Austrian Tunneling Method (NATM) for primary support design (see Ueblacker, Horst, “Feasibility Study and Preliminary Design, Hanging Lake and Reverse Curve Tunnels, Glenwood Canyon, Colorado”, Proceedings: International Symposium on Unique Underground Structures, Denver, Colorado, USA, June 12-15, 1990, pp 30-1 to 30-20).