Twin Light Rail Transit Tunnel & Underground Lindbergh Terminal Station Minneapolis-St. Paul Metropolitan Airport

The Hiawatha Light Rail project represents the first LRT line to be developed in Minnesota. Upon completion, the 12-mile Hiawatha Line will link three major areas within the Twin Cities: downtown Minneapolis, the Minneapolis-St. Paul International Airport, and the Mall of America in Bloomington.

The airport segment consists of bored running tunnels, cross passages, and the Lindbergh Terminal Station at the Minneapolis-St. Paul International Airport for the Metropolitan Airports Commission.

The overall lengths of the tunnels are 7400 ft each, with 10 cross passages, nine of which are tunneled and one is cut-and-cover. The tunnels pass under active runways and taxiways and were mined without disruption to air service. Ground conditions are comprised of fills over a limestone cap underlain by a shale band, which is underlain by soft sandstone. The sandstone is a peculiar material with a tendency to “peak” above the crown of a circular tunnel. A buried valley filled with water bearing glacial deposits intersects the bored tunnels along the alignment, immediately underneath the airport. Soft ground is also present at the north and south portals.

The bored tunnels are 18 ft 10 in internal diameter with a 10 in thick precast concrete bolted segmental lining. Construction was carried out using an EPB machine with foam conditioners. The station is a large cavern approximately 54 ft wide x 36 ft high, excavated beneath the limestone cap. Rockbolting of the limestone is all that was required for support, but a precast lining was installed for waterproofing and as an architectural finish. The overall station length including ancillary space is 530 ft, with a platform length of 280 ft.

HMM was responsible for the design of the bored tunnels, including the lining, settlement analysis, design of cross passages, and the tunnel ventilation system. We performed an advisory and peer review role for station planning and fire/life/safety, including fire protection and exiting, risk assessment, and provided advice on contractual issues for underground works, including General Conditions, DRB, GBR, etc. HMM also developed the cost estimate for the bored tunnel and cross passages.

Project Highlights:

• Advisory role on transit planning
•  Planning construction work within a busy airport environment
• Tunneling in difficult ground conditions