FHWA TRIES PERFORMANCE SPECS

The construction is described of a dangerous 4-mile section of U.S. Route 25E providing a vehicle tunnel and its approach roads. The difficult ground, the testing specifications, and the shotcrete testing are described. The details of the construction are described, in which working from a pilot tunnel, the crew woked for 3 months to stem the flow of water before tunneling reached the cavern. The cavern roof was shored, a siphon was constructed under the alignment of the tunnels, and 1,500 cu yd of concrete was pumped in to fill the cavern 15 ft beyond each side of the future tunnel. The ground support systems varied to meet the five categories of geology ranging from poor to good. It is described how the Federal Highway Administration wrote performance specifications for the reinforced shotcrete. Specifications required shotcrete strength to be demonstrated by using ASTM C 1018 standard test methods. NATM (new Austrian tunneling method) excavation with four heads is described. A more efficient firing system for blasting is also noted. These and other highlights of the construction are summarized.