The design of section e-5 tunnels of the washington metro using the new austrian tunneling method (natm) is described. The twin-boretunnel section, approximately 1, 000 ft long, runs directly beneath fort totten park in washington, d.c., west of the district's border with prince george's county, maryland. In addition to a conventionaltunnel design, metro engineers directed an alternate design using natm. Although this type of design is used extensively in europe, this will be one of the first natm applications to soft-ground tunnels in the united states. The natm is a method whereby the rock or soil formations surrounding a tunnel are integrated into an overall ringlike support structure; thus the formations become part of the support system. The two main support elements are a reinforced shotcrete initial lining and an unreinforced final concrete lining. The tunnelswill pass entirely through a cretaceous formation of stiff, silty clays and clayey sands. Natm appears to be a suitable method of constructing these tunnels because the soils apparently possess good standup time, the groundwater table is low, and the tunnels are relatively short. Even though these tunnels have not yet been constructed, it is believed that the design concepts presented will be useful to tunnel designers. This paper appeared in transportation research record no. 1150, tunneling. For covering abstract see irrd no 818446.
Samenvatting