Whether in urban or environmentally sensitive areas, CNA engineers have the design expertise and technology to utilize trenchless techniques rather than large trenches. This allows for minimum disruption of the surface area. Techniques include conventional tunneling, pipe jacking, microtunneling, and horizontal directional drilling (HDD).
Lake Minnetonka Area Tunnels and HDD
CNA was the tunnel and HDD designer for three tunnels and one HDD lake crossing for a sanitary sewer project. The HDD consisted of dual 8-inch pipes under a portion of Lake Minnetonka.
The tunnels were constructed through saturated soil and clay. The HDD consisted of dual 8-inch pipes under a portion of the lake.
The tunnel pits were designed to withstand the high groundwater table while using helical piles to help support the pit base.
Pilot Tube Microtunneling
CNA was the prime engineer for a 75 ft. long sanitary tunnel in the Twin Cities. The new 8" diameter PVC pipe runs through a myriad of soils from glacial tills to alluviums and under numerous utilities. The design entailed special methods for tunneling through the varied soils while being limited to 12 ft. diameter tunnel shafts.
Sanitary Sewer Pipe Jacking & HDD II
CNA designed two 48" steel casing pipe-jacked tunnel crossings under a highway as well as 820-ft long HDD twin forcemains.
CNA provided design, specification, a Geotechnical Baseline Report, and construction observations.
