Implementation of Conventional Tunneling in a Design-Build Contract in the US

Synopsis:

Historically, conventional tunneling also referred to as NATM and more recently SEM in the US has been executed in a design-bid-build contractual framework. With the increased use of the design-build contract for tunnel projects NATM is currently being executed under this contract form on Washington’s new Silver Line extension and is believed to be one of the first such applications in the US. The extension will provide Washington DC metro’s access to Dulles International Airport and significantly relieve traffic congestion in the Northern Virginia region located just south-west of the nation’s capital. The method, by its design philosophy, requires openness to adaptation and flexibility of support installation in the field depending on ground conditions encountered.

Experience with the design process and on-going tunnel excavation, and support during construction indicates that the design-build allows for a more efficient application of the method mainly because designer and contractor work closely together starting early in the design stage and continuing through execution. The proposed paper will report on the status of this important infrastructure project and concentrate on the on-going tunneling which features shallow NATM in soft ground at city environment below streets with a series of pre-support methods and will contrast advantages and disadvantages of design-bid-build vs. design-build for conventional tunneling.

Implementation of Conventional Tunneling in a Design-Build Contract in the US
2010 World Tunnel Congress and 36th ITA General Assembly Proceedings
May 14-20, 2010
Vancouver, British Columbia, Canada