Abstract:
The Twin Ports Interchange (TPI) project is the largest and most complex ground improvement project undertaken by the Minnesota Department of Transportation. Located in Duluth, Minnesota – and locally nicknamed the “ Can of Worms” project – the interchange forms the junction of I-35 from Minneapolis/St. Paul; I-535 from Superior, Wisconsin; and TH 53 from northern Minnesota’ s Iron Range. The interchange has been redesigned to convert many of the low-profile bridges into earthen embankments alongside new overpass and flyover bridges. New embankments feature several MSE retaining walls to accommodate abrupt grade changes.
Subsurface conditions across the project generally consist of soft organic soils and lacustrine clays, dense alluvial sand, and uncontrolled industrial fill to variable depths and thicknesses. The dense alluvial sand, in particular, is not consistently present throughout the site. Groundwater is shallow. Historical industrial activities at the site have contributed to a range of environmental impacts throughout the soils and groundwater.
New roadway embankments are supported on an extensive ground improvement system to mitigate settlements and lateral deformations. The ground improvement system generally consists of rigid full displacement concrete columns supporting compacted aggregate load transfer platforms (LTP). Because of the subsurface soil variability, the wide range of MSE wall and embankment geometries, and the presence of adjacent bridges on separate driven pile foundations, the design utilized advanced 2D and 3D numerical modeling to analyze the numerous soil-structure interactions, column installation effects, and overall ground improvement performance.
The presentation will describe the complex ground conditions and project constraints, provide details of the multiple stages of numerical modeling and their impacts on design, and share geotechnical monitoring data that compares modeling predictions and construction performance.