As one of the Twin Cities’ major thoroughfares, Trunk Highway 169 runs north and south through the heavily populated west metro. In fall 2016, the Minnesota Department of Transportation kicked off four projects in a bid to improve driver safety and accessibility along a segment of TH 169 stretching between the suburbs of Hopkins, Edina, Minnetonka and St. Louis Park. One of the projects involves the demolition and replacement of a 3,300-foot-long bridge over Nine Mile Creek.
As a member of the project team led by general contractor Ames Construction, AET has been providing geotechnical engineering and construction quality management to support the construction of the new roadway. In our role, we have also worked closely with design engineer Alliant Engineering and MnDOT. This is the fifth design-build project we have teamed with Ames Construction and Alliant Engineering.
The existing bridge was demolished in January 2017 and will be replaced with a causeway. Because of the deep organic deposits that extend through the length of the project, the causeway will be supported on controlled modulus columns (CMCs). CMCs are used to improve the soils characteristics of weak ground and to reduce imposed settlements caused by the proposed structure. CMCs are installed using a specially designed auger that displaces the in situ soils laterally, introducing cementitious materials with virtually no vibration or spoils. This helps to stabilize soft soils and confine any soil contaminants.
Following the placement of the CMCs, the project team will construct the roadway embankment as well as the mechanically stabilized earth retaining walls that have been designed with storage capacity for flood water in the Nine Mile Creek Watershed. Once these items are complete, the team will place six lanes of concrete pavement and concrete shoulders.
David Rettner, PE, is president/principal engineer at AET. He can be reached at drettner@amengtest.com
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