CNA Engineer s provided design team engineering for the Lafayette Bluff Highway Tunnel project in Two Harbors, Minnesota. The Lafayette Bluff highway tunnel is located on the environmentally and aesthetically sensitive North Shore of Lake Superior and opened to traffic in the fall of 1991. The tunnel was part of an eighteen year, $104 million program to upgrade US Route 61 in northeastern Minnesota.
The existing highway was threatened by steep, unstable cliffs and contained tight curves not meeting current design standards.

This project consisted of open cut rock slopes for the approaches, 197 feet of portal structure or cut-and-cover tunnel and 652 feet of mined rock tunnel. The sharp four-degree curve of the new alignment required additional tunnel width to provide sight distance and resulted in a 61 foot wide excavation, making Lafayette Bluff among the widest hard-rock highway tunnels in the United States.

The tunnel was constructed in a closely-jointed, variable-weathered diabase rock mass. Rock cover above the tunnel crown ranged from about 13 feet to about 89 feet. For approximately 60% of the tunnel length, the cover was less than the tunnel width. A tunnel project was chosen rather than an open cut project due to environmental, economic and right-of-way reasons. Rock support and lining consisted of external portal beams, rockbolts and reinforced shotcrete. A final concrete lining provided structural support for the rock mass and the membrane waterproofing system.

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Starting in 2002, four cut and cover tunnels were constructed for the Metropolitan Airports Commission  at the MSP International Airport. Our engineers designed and performed field quality assurance observations for the waterproofing systems. A total of 1 million square feet of waterproofing was installed.
Four tunnels were constructed below the water table. Zero leakage was required to prevent ice buildup during the long winters. A double waterproofing layer with internal drainage was designed. CNA Engineers performed quality assurance observations for three tunnels and was the Quality Control Manager for all aspects of construction of the fourth.

CNA Engineers provided design and construction services from 1999 through 2004 for the Minneapolis / St. Paul Light Rail Transit (LRT) Station and Tunnels project. The project included a 7,400-foot-long, 21-foot-diameter bored tunnel, and a 540-foot-long, 60-foot-wide by 40-foot-tall mined transit station under the Minneapolis International Airport. CNA provided: feasibility study, Geotechnical Exploration Program, Data Report and Baseline Report, mined tunnel and cross passage tunnel initial and final support, mined station initial support, final lining and waterproofing, tunnel and station instrumentation, tunnel portal structures. During construction, our firm provided observation and coordination as well as construction engineering and project administration.

We were the prime design consultant for the Silver Creek Cliff Highway Tunnel project that was completed in July, 1994. The Silver Creek Cliff highway tunnel was part of a $104 million program to upgrade US Route 61 in northeastern Minnesota.

The Federal Highway Administration awarded both the 2002 Excellence in Highway Design Award and the Rural Highways Merit Award to CNA Engineers for their participation in this project.

The tunnel was constructed in a closely-jointed diabase rock mass, with numerous thick infilled seams intersecting the tunnel. The arch-shaped tunnel was excavated 53 feet wide by 36 feet high and finished 46 feet wide and 31 feet high. Tunnel excavation was by controlled blasting, with multiple top headings and benches. Rock support and lining consisted of external portal beams, rockbolts and reinforced shotcrete.