Lemay Pump Station No.1 Redundant Force Main Tunnel

Summary

Kaskaskia Engineering Group, LLC (KEG), as a sub-consultant to Shannon & Wilson, Inc., provided a senior geotechnical engineer as a Resident Project Representative (RPR) and Administrative Staff to the Construction Management Team (CMT) for this Metropolitan St. Louis Sewer District (MSD) project.

Project

The project consisted of the construction of the Lemay Pump Station No. 1 Redundant Force Main, which was a 96-inch diameter force main, approximately 0.62 miles long constructed up to 175 feet below surface grades in a carrier tunnel.  The carrier tunnel required the construction of a 30-foot diameter vertical entry shaft approximately 175 feet below ground and a 25-foot diameter vertical exit shaft approximately 130 feet below ground.  The tunnel alignment passed below an existing active force main tunnel and below the River Des Peres near its confluence with the Mississippi River.

The carrier tunnel was an 11.25-foot diameter tunnel, up to 175 feet deep, bored through hard limestone bedrock using a tunnel boring machine (TBM).  KEG’s RPR provided a construction QA/QC downhole on the TBM while the carrier tunnel was advanced.  KEG’s RPR logged an estimated rock and groundwater conditions, including any jointing or fracturing in the rock which could impact the stability of the tunnel.

KEG’s RPR also observed the installation and testing of rock bolts in the crown of the tunnel for roof support and provided recommendations for the installation of additional rock bolting or roof support as the tunnel was advanced.  The carrier tunnel was successfully completed with no lost-time accidents or significant impacts to the construction schedule due to bedrock or groundwater conditions.