The Cumberland Gap Twin highway tunnels are currently under construction. In 1986 a pilot tunnel was excavated at the crown of the southbound tunnel to investigate the geologic conditions along the 4,200 ft length of the twin tunnels. This paper describes the evolution of the instrumentation program associated with the excavation of the pilot tunnel. The instrumentation program as initially conceived had research as a primary objective. The initial program was reduced to a moderate number of extensometers, convergence points, strain gauges on steel sets, piezometers, and groundwater flow weirs for the bid documents for the pilot tunnel excavation. After about 15% of the tunnel had been excavated, the instrumentation program was again reduced substantially because the initial data indicated that the scope of the program could be reduced while still providing sufficient data for designing support of the main tunnels. The paper presents the results of the instrumentation program and concludes with recommendations regarding instrumentation programs for pilot tunnels. This paper appears in Transportation Research Record No. 1277, Modern geotechnical methods: instrumentation and vibratory hammers 1990.
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