The New Austrian Tunneling Method (NATM) has found slow acceptance in the U.S. Washington Metropolitan Area Transportation Authority, among the first to utilize this system, found its NATM contractor for the Wheaton Station portion of its Red Line came in at $30 million below engineering estimates for this segment and a value engineering change slashed an additional $20 million. NATM takes in account equally geotechnical and structural considerations with geological formations surrounding the excavations considered as both a load exerting and load carrying ring. Steel reinforced concrete lining is eliminated with ground and the initial shotcrete support carrying loads. The initial support has to be applied on time and in tight contact with the ground. NATM achieves its maximum cost effectiveness in Europe where representatives of owner and contractor confer during excavation and agree on the encountered conditions. Anticipated conditions are described in design documents as ground types and are linked to support and excavation patterns. Because contract costs are based on unit prices, there is more risk sharing than is typical of U.S. contracting practices.

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Filing Info

  • Accession Number: 00454972
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 31 1988 12:00AM