Metropolitan St. Louis Sewer District (MSD) St Louis, Missouri, United States
Improving urban wastewater management through precision tunnel boring
Tunneling 21,000 feet through challenging subterranean soil
An Alberici joint venture constructed a four-mile long sanitary sewer tunnel for the Metropolitan St. Louis Sewer District (MSD), which served as a key connection for two major wastewater treatment facilities that combine to treat more than 300 million gallons of wastewater each day. The project required tunneling through 21,000 feet of porous limestone and shale at depths of 200 feet, crossing under the Meramec River twice and interconnecting with centuries-old infrastructure beneath the streets of St. Louis.
Multiple large-diameter shafts
To excavate and line the tunnel, Alberici lowered a tunnel boring machine down a 36-foot-wide access shaft that included a 200-foot-long launch chamber at the bottom. Alberici also constructed a massive, 100-foot-wide lift shaft using drill-and-blast excavation techniques.
Other key features and components
Additional access shafts and de-aeration chambers were constructed at five sites along the tunnel. Alberici also installed a rail system to help move 12-foot-long precast concrete tunnel pipe sections into place that formed the walls of the tunnel.
Safe, efficient shaft excavation
To prevent collapse of the shafts during excavation in the loosely packed soil, Alberici installed panels filled with bentonite clay slurry. Once the bentonite was in place, crews set reinforcing steel cages and then began placing concrete. This process created a reinforced concrete cylinder that allowed the shafts to be safely excavated.