The 1 1.6 mile (18.7 km) long Hiawatha Light Rail Transit Line is the first of its kind built in Minnesota and one of the state’s largest public works projects at a cost of $676 million, second only to the multi-billion dollar expansion of the Minneapolis-St. Paul International Airport. Twin precast concrete tunnels run parallel beneath the heart of one of the nation’s busiest airports for a total distance of 7400 ft (2250 m). Formidable subsurface challenges, concern for water infiltration, and aviation related restrictions led to the selection of the $1 10 million bored precast concrete tunnel lining system. Each tunnel ring was constructed with seven bolted precast concrete segments with compression gaskets ensuring watertight connections as a backgrouting operation maintained continuous ground support. A custom-built 70,000 sq ft (6500 m2) precast production facility housed a carousel assembly production area with 13 stations, including those for welding, curing, and gasket installation.
