Metropolitan St. Louis Sewer District (MSD) St Louis, Missouri, United States

Improving urban wastewater management through precision tunnel boring

Baumgartner Tunnel tunneling

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.

Baumgartner Tunnel large shafts

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.

Baumgartner Tunnel shaft

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.

Baumgartner Tunnel safe shaft excavation

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.