Barr worked with the City of Minneapolis to evaluate the pressure within its tunnel system and prevent the explosive release of air-water mixture at the dropshaft. We developed models to simulate the tunnel system’s hydraulics and evaluated transient flows (also known as pressure surges) within the tunnel system and the release of large air pockets—both of which can cause a geyser. The model was calibrated using pressure readings in the tunnel during three storm events.
After the model was calibrated, Barr used it to develop hydraulic design criteria for a deflector plate at the top of the dropshaft that would redirect a geyser into a surge chamber located below the street. The model was also used to size the surge chamber. In addition, Barr completed an on-site inspection, utility locate, and civil and structural design services.