At one time, the Poplar Street Bridge was one of only two U.S. bridges that carried three interstates (I-70, I-55 and I-64) across a river. In 2012, after many years of planning, a three-phase proposal was adopted to alleviate bridge safety and transportation concerns. The final phase of the project, currently underway, includes several impressive engineering feats that rely heavily upon geotechnical services provided by Geotechnology Inc.
The project entails extending a third lane of I-64 across the PSB by widening the bridge. This is being accomplished by moving four lanes of I-64 nine feet to the south side of the bridge to add the new lane. The shift is the second-largest bridge slide done in U.S. history.
Another major design change takes two separate two-girder structures and alters them into a single four-girder bridge. To support a new section of the road, the project calls for the river piers to bear the additional load, rather than installing additional foundations. Two new foundations were built on the anchor piers.
Before any of these plans could be executed, the rock and soil beneath the bridge and the Illinois approach had to be explored and evaluated to determine if conditions could bear the weight of the changes, and if not, how to meet these challenges.
In 2013, Geotechnology began engineering services which included drilling, sampling and testing the rock and soil conditions. The firm drilled 12 borings (six piers on the bridge and six piers on the Illinois approach) and used Load and Resistance Factor Design methods in their analysis.
Based upon the results and analysis of its subsurface exploration, Geotechnology made recommendations for the geotechnical aspects of the design and construction of the project including available foundation resistances of the existing foundations.
Since the two anchor pier modifications were impacting the St. Louis floodwall and the Illinois levee, Geotechnology also worked with HDR Engineering Inc., to obtain a Section 408 permit through the U.S. Army Corps of Engineers.
The design team had to prove that the changes to the flood protection structures were not injurious to the public’s interest. This required Geotechnology to perform seepage and stability analyses and generate job specific special provisions for construction.
“We are very pleased to have played a vital role in this collaborative effort that tremendously improves our region’s infrastructure,” said Craig Kaibel, P.E., Geotechnology’s specialty testing and deep foundation testing manager.