Evaluating Mitigation Measures to Prevent Geyser Events in the City of Minneapolis Tunnel System

Nels Nelson Memorial Award Ceremony: 

Award Winner: Vinicius Taguchi, Masters Student in Civil, Environmental, and Geo- Engineering

 

Keynote Speaker: Christian Frias, PhD, PE; Barr Engineering

Geysers in stormwater tunnel systems have been observed in many cities, including Edmonton, Chicago, Manitou Springs, Minneapolis, Montreal and Pittsburgh. Research indicates that the geysers are caused by a violent release of air-water mixtures coming from trapped air pockets in tunnel systems. Over the past few decades, there have been many efforts to predict geyser events and to design mitigation measures to prevent or control them.

Two-phase flow (air/water) computational fluid dynamics (CFD) models were developed to simulate observed geyser events and to evaluate design alternatives for geyser mitigation measures on a tunnel segment in the City of Minneapolis, MN.  Both open source and commercial software were used to develop these models. The CFD models were validated using observed data such as pressure, geyser height and manhole maintenance records. The observed data was complemented with results from precursor hydrology models (i.e. velocities and pressure values for different locations in the tunnel). The model results allowed an informed decision on geyser mitigation alternatives based on parameters such as geyser height, force on the manhole cover and volume of water expelled per geyser event. Finally, three design alternatives were evaluated. The goal was to either contain the water expelled by the geyser (using a surge chamber and an oversized manhole) or to avoid the violent release of air-water mixture (using a modified tunnel connection).