A Quarter Century of Geotechnical Research

Appendix B - Tunneling Geotechnology

In the early 1970's, the U.S. Department of Transportation (DOT) initiated a major research program in tunneling that was divided among four DOT agencies. Most of the technical aspects were divided between the Federal Railroad Administration (FRA) and FHWA. Improved tunnel linings and excavation techniques were the responsibility of FRA; FHWA handled site investigation, tunnel instrumentation, cut-and-cover tunneling, and ground movement and prediction control. Justification for the research program was based on projected demands for transportation tunnels increasing from two to three times during the 1970's and doubling again in the 1980's and 1990's, for a total of almost $30 billion by the end of the century. It was also estimated that 50 percent of all highway tunnels would be built in an urban environment by cut-and-cover techniques. Research aimed at improving the design and construction of tunnels could reduce costs by at least 30 percent.

Overruns in cost and time were common in highway tunnel construction projects during the 1970's, mainly because of unforeseen ground conditions due to inadequate site investigations. Most of the FHWA research effort was concentrated on improving our knowledge of predicting and controlling these problems, which were obviously geotechnical in nature. The project was concluded in 1983 and a summary report was distributed in January 1985 (FHWA-RD-85-016).

That summary gives an overview of research conducted for FCP Project 5B, Tunneling Technology for Future Highways. That project was aimed at research, including state-of-the-art tunneling techniques unknown in the United States although accepted by other countries, and more experimental tunneling techniques not yet generally accepted. Specific research studies dealt with cut-and-cover tunnels, site investigation, earth movements, environmental criteria, and supporting activities (research conferences, information exchange, etc.).

The report summarized research on: costs, classical ground control techniques, slurry walls, tie backs, anchors and grouting for cut-and-cover tunnels; planning of site investigations, direct mechanical measurement (pressuremeters, cone penetrometers, vanes, piezometers) of soil properties, and indirect measurement by sensing techniques (aerial photography, acoustic, seismic, and electromagnetic systems); prediction and control of ground movements, including phenomenological study and development of lining techniques; and guidelines for the environment, including air movement and pollution, tunnel lighting, traffic operation, driver behavior, safety and fire hazards.

The report fully documents major research advances, significant design and analysis improvements, and substantially new recommendations in areas ranging from analytical modeling to soil property evaluation. The summary report also gives a comprehensive listing of the major reports that resulted from each study, some of which were and still are benchmark references for geotechnical and structural engineers today. This summary report on the U.S. DOT Tunneling Project is a must-read and must-have document for a transportation engineer's personal library.