Improved Subway Construction for the 21st Century

Abstract

Despite many innovations and advances in technology, subway construction remains a challenging and taxing proposition, even under the best of circumstances. Given the enormous cost of subway construction and the impact of construction activity on overlying neighborhoods and communities, subway projects can attract adverse publicity and the associated negative public perception of the mass-transit industry. Major cost and schedule overruns are not uncommon. Witness, for example, the bad press that the Los Angeles Metro's subway construction recently attracted in the local and the national press. Against this backdrop, there is a clear need for reviewing the state of the art and for examining the range of options available to owners for minimizing the trials and tribulations of subway construction activity. Drawing upon experience from major subway system construction projects in the United States, particularly the Washington Metropolitan Area Transit Authority (WMATA), and from elsewhere, this study sets out to achieve this objective. Various tunneling methods, including the two-pass, single-pass, the New Austrian Tunneling Method, and the like, are discussed and strong and weak points evaluated. Also discussed are the selection of tunnel boring machines, ground modification techniques, mitigation of environmental impacts, contract format and payment methods, and risk management strategy from the owner's viewpoint. Recommendations are made for developing tactics and strategies to better manage and control the subway construction process. In sum, the paper provides timely information on an important issue typically involving high visibility mega-dollar construction projects.