Constructing a Stormwater Storage Facility in a Glacial Valley Using CMGC Project Delivery-Video

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Video Summary

The presentation describes the I-35W stormwater storage project in Minneapolis, built to reduce flooding at a highway low point where the existing drainage system could not handle major storms. Because the site is narrow, has high groundwater, and lies in a buried glacial valley with difficult soils and boulders, the team designed six interconnected underground storage cells, each about 42 feet wide and 84 feet deep, using diaphragm walls and top-down construction. During storms, excess water spills from the existing pipe into the cells; afterward, a pump returns it to the drainage system.<br /><br />The project used a Construction Manager/General Contractor (CMGC) approach, involving the contractor early to improve constructability, cost, schedule, and risk management. Collaboration led to design changes, including placing the weir inside a storage cell and selecting pumping over costly gravity-drainage alternatives. The team also agreed on transparent methods to document and address obstructions encountered during excavation.

Keywords

I-35W stormwater storage

Minneapolis flooding mitigation

underground storage cells

CMGC construction approach

diaphragm walls

stormwater pumping system