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Civil & Marine, Water

Baumgartner Tunnel

St. Louis, Missouri

Improving urban wastewater management through precision tunnel boring


Civil & Marine


Key Services



The challenge

The construction of a four-mile-long sanitary sewer tunnel for the Metropolitan St. Louis Sewer District (MSD) presented several significant challenges. Tunneling through 21,000 feet of porous limestone and shale at depths of 200 feet required precise engineering and excavation techniques. Crossing under the Meramec River twice and interconnecting with centuries-old infrastructure beneath the streets of St. Louis demanded careful planning and coordination to ensure the tunnel’s integrity and avoid disruptions to existing infrastructure. Moreover, working in loosely packed soil posed risks of shaft collapse during excavation, demanding innovative solutions to ensure worker safety and project progress.

Key Facts

4-mile-long tunnel

200+ feet underground

100-foot-diameter shafts

Challenge met

To overcome these challenges, Alberici implemented advanced tunneling technology and construction methodologies. Lowering a tunnel boring machine down a 36-foot-wide access shaft with a launch chamber at the bottom enabled efficient excavation through the challenging limestone and shale formations. The use of drill-and-blast excavation techniques for a massive, 100-foot-wide lift shaft provided a robust foundation for tunnel construction. The installation of a rail system facilitated the precise placement of precast concrete tunnel pipe sections, forming the walls of the tunnel. To prevent shaft collapse during excavation, Alberici employed panels filled with bentonite clay slurry, creating reinforced concrete cylinders to ensure the safety of the workforce and the structural integrity of the shafts. Through meticulous planning, innovative technology, and expertise in underground construction, Alberici successfully completed the sanitary sewer tunnel project, establishing a critical connection between major wastewater treatment facilities in St. Louis.

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