The I-94 and Sargent Road Interchange is a key transportation route for this area – especially when Michigan International Speedway is holding a race or the University of Michigan is hosting a football game. When MDOT began considering a major reconstruction of this area, the team understood careful planning would be required to keep traffic flowing. What was not so apparent was how subsurface conditions would increase project complexity.
The project included replacement of the Sargent Road Bridge over I-94, replacement and/or realignment of the ramps to and from I-94, and realignment of 3,200 feet of Sargent Road.
- The realigned segment of Sargent Road and portions of the realigned ramps (with embankments up to 24 feet high) were to be constructed through significant wetland areas with up to 6 feet of peat, muck and organic silt at the surface, underlain by up to 39 feet of loose granular soils. Construction could not proceed without treating these soils.
- G2 performed extensive engineering analyses to identify methods to accelerate and monitor embankment settlement while maintaining stability. The soft and organic soils were too deep and widespread to be cost effectively removed by conventional undercutting or rolling surcharge methods.
- G2 developed a staged embankment construction plan incorporating a drainage/stabilization blanket and wick drains to accelerate consolidation of the compressible soils. Instrumentation systems were installed to record how much settlement was occurring during embankment construction to avoid causing slope instability by overstressing the underlying weak soils.
- G2 recommended additional surcharge fill over the embankment fill to further accelerate settlement and over-consolidate the soils to facilitate earlier construction. G2 prepared all the Special Provisions related to subgrade undercutting embankment and surcharge construction, wick drain installation and geotechnical instrumentation.
Embankments were constructed in less than 3 months, enabling the remainder of construction to proceed on schedule with minimal disruption to I-94.