Minneapolis and adjoining Saint Paul make up the “Twin Cities”, but were you aware of the fantastic world that lies under them? Mike Heuer, a geotechnical engineer says "You go down 30 feet and it's an entirely different world." The vice president of Mortenson Construction, Dan Mehls says "The Vikings stadium is sitting on very, very stable soil." He also says that the Target Field and the Target Center are the engineering marvel.
Ancient river beds run under the area and there are valleys formed by the glaciers 12,000 years ago. Everything now is filled with unstable soil.
Mehls and Heuer worked on all three of the professional stadiums in Minneapolis.
Heuer admits that Target Center is his favorite due to the fact that the building stands on three different formations, including an ancient subterranean cliff. "It's very unique. In fact, I don't know of any other building in Minneapolis, in Minnesota that has three different foundation systems." he said.
The geology of the Twin Cities and Minnesota looks like a layer cake. Tom Hickson, professor at University of St. Thomas describes "If you could pull away all that overlying geology, it would be like you were standing at the edge of a canyon looking down at a river canyon there."
Under the Target Field there is a river bed, which is bigger and wider than the Mississippi River. This means that thousands of pipes into the ground were needed for supporting the outdoor stadium. "Target Field itself sits on over 4,000 pipe piles, 10 inch diameter pipes that are driven over 100 feet into the ground because the area there was an old river bed deeper and wider than the Mississippi River." said Mehls.
The geologist Greg Brick said "I think people would be completely amazed to know there is this very interesting geological feature right under their feet. It is so large that a reporter that went down there in 1939 called it the 'Lost World'."
Source: KARE 11