AET Senior Geotechnical Engineer, Joe Bentler, presentation earlier this month at the 64th Annual University of Minnesota Geotechnical Engineering Conference.
His talk, titled, “Widening the Wisconsin Approach to the I-90 Dresbach Bridge over Soft Floodplain Soils” described the geotechnical design, construction, and monitoring of the Wisconsin approach embankment to the new I-90 bridge, an area of soft floodplain soils.
Four main takeaways about the project include:
1. A performance-based specification for the embankment widening required that additional subsurface investigation be performed during the construction phase. This worked analogous to a “mini” design-build process
2. With flexibility in choosing a ground-improvement method, the contractor chose to excavate the near-surface organic soils (leaving the deeper compressible clays in place), backfill with sand, construct the embankment, and surcharge for several months
3. Design assumptions were confirmed by use of extensive geotechnical instrumentation (piezometers, earth pressure cells, and ShapeAccelArray “inclinometers”), using an automated datalogger connected to a cellular modem.
4. Remote monitoring of the field instrumentation allowed AET engineers to observe stresses and displacements during embankment construction, allowing for comparison with design assumptions