Wet weather events in Minneapolis have at times created surcharging of the existing stormwater tunnels to the point where manhole lids are blown off by water force and causing a hazard to I-35W travelers. Recognizing the need to mitigate these occurrences, Minnesota DOT went through a series of preliminary assessments. In 2017, the team of Brierley Associates, Barr Engineering and TKDA was selected by MnDOT to design a subsurface stormwater storage facility along I-35W south of Minneapolis, that will also provide flood relief of an existing low area near 42nd street.

The final design is comprised of six 45-ft diameter by 90-ft deep somewhat circular interconnected cells to provide over 4.5 million gallons of storage. Given the limited space along I-35W, the cells will be constructed using diaphragm wall methodology.

Brierley Associates is the Engineer-of-Record for the underground design components including the six interconnected diaphragm wall cells.

Construction is scheduled to commence in 2020 and will be executed through MnDOT Construction Manager General Contractor (CMGC) project delivery.  During construction a monitoring program will be utilized to monitor in near real-time groundwater, movement, and stresses during construction and throughout the life of the structure.

Click here for a video rendering of the project (Courtesy of Barr Engineering).