CNA has been designing new tunnels and tunnel rehabilitation projects since 1979. We have been involved in almost every deep tunnel constructed in the Minneapolis-St. Paul area and have extensive experience with projects around the country. Our engineers are tunnel experts with vast knowledge of construction techniques and equipment for both new construction and rehabilitation projects. Nearly all of these projects involved design of associated shafts. CNA can respond to any circumstance in underground facilities that may be presented.
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Rehabilitating aging underground infrastructure is one of CNA's key areas of expertise. We routinely design repairs involving deficiencies such as concrete liner replacement, void filling, crack sealing, cure-in-place lining, grouting and settlement repairs.
Tunnels & Shafts
Sanitary Sewer Tunnel
CNA designed and provided construction observations for a 7500-ft-long sanitary sewer tunnel and three tunnel crossings. A 60-inch reinforced concrete pipe was installed inside a ringbeam and lagging tunnel. We also designed numerous shafts for construction access and ongoing maintenance. The short tunnel segments were constructed under active railroad tracks
Utility Tunnels
CNA provided engineering and construction administration services for the steam utility tunnels and shafts of this project. Three tunnels were designed, the 1450-ft-long deep tunnel is arch shaped and was constructed in sandstone.
The shallow tunnels were constructed in soil. Two shafts were designed and constructed and included an elevator, utility lines and stairs.
Storm Sewer Tunnel
The existing storm sewer tunnel system consists of 4 miles of storm tunnel in a metropolitan area. CNA designed a new 4200-ft long parallel tunnel to relieve the existing system of surcharge. The tunnel cross sections were designed to take advantage of the bedrock geology. The chosen rectangular and cathedral shaped cross sections required less ground support than other shapes. A large outlet structure in the river, multiple junction structures, and large access shafts were also part of the design.
Sanitary Sewer Rehabilitation
This 8000-ft-long, 6-ft-diameter fiberglass reinforced polymer mortar pipe had cracked sections leaking groundwater. CNA was retained by the client to inspect and design repairs, and construction administration services..
During inspection, CNA discovered that the space between the pipe and ringbeam and lagging initial support was not fully filled with grout, which combined with the water table elevation, led to the fractured sections of pipe.
The cracked tunnel sections were repaired at the same time as the annular space was grouted.
