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IDOT Pontoon Road, High Speed Rail Grade Separation

Owner/Client: Illinois Department of Transportation (IDOT)
Location: Granite City, Illinois
Services: Geotechnical, Construction Materials Testing

Geotechnology provided geotechnical and construction observation services for preliminary and final design phases for single- and multi-span bridges that provide a grade separation at Nameoki Road and a four-rail, at-grade crossing in Granite City, Illinois.

The high-speed rail grade-crossing project included design and construction to replace a four-rail, at-grade crossing with a grade separation that includes a single-span bridge carrying Pontoon Road over Nameoki Road to meet the elevation of a multi-span bridge over the rails. One of the four rails carries Amtrak and will include the St. Louis to Chicago high speed rail tracks.

Bridge foundations are supported on end-bearing H-piles. Mechanically-stabilized earth (MSE) walls support both sides of the approach embankment east of the single-span bridge and between the single and multi-span bridges. Special concern from a geotechnical vantage was the soft soil conditions in the embankment and MSE retaining wall foundation areas. Recommendations addressing soft subgrade soil conditions included:

  • A geogrid-reinforced aggregate mat below the east approach embankment and between Nameoki Road and the railroad tracks
  • Wick drains
  • Partial removal and replacement of soft subgrade soil
  • Staged construction under various portions of approach embankments

Services during construction included vibration monitoring during pile and sheet pile driving, and fill control and field density measurements during embankment placement. Pre-construction services included environmental surveys on properties that were purchased during right-of-way acquisition and asbestos surveys of 50 residences and commercial structures that were demolished.