Gasconade River Bridge Foundation Remediation

Built in 1955, the Interstate 44 Gasconade River Bridge in Laclede County, Missouri was slated for replacement. The Missouri Department of Transportation (MoDOT) had begun construction of a temporary substructure north of the existing bridge to support a new replacement bridge deck. MoDOT planned to complete the new deck, then remove the old deck and slide the new deck into place onto the existing bridge foundations. For this reason, the integrity of the existing bridge foundations was extremely important.

MoDOT contacted GeoEngineers to discuss concerns about the rock’s integrity beneath one of the bridge bent or pier foundations. MoDOT initially requested that GeoEngineers perform a geophysical exploration of the subsurface beneath the bridge bent in question. After MoDOT drilled additional borings and decided to close the bridge to traffic, the agency asked GeoEngineers to expedite the geophysical evaluation. In response, GeoEngineers mobilized to the project site and worked through the weekend to acquire and interpret the geophysical data.

GeoEngineers used geotechnical and geophysical data along with available geologic information to form a reliable characterization of the subsurface area surrounding the bridge foundation of concern. GeoEngineers concluded that hollow spaces in the subsurface appeared to be limited in size and extent and were not very large, “room-sized” voids.

Based on the evaluation of the subsurface area, the project team recommended pressure grouting to fill the voids, remediating the subsurface conditions beneath the bridge foundations. At MoDOT’s request, GeoEngineers’ staff provided construction observation, documentation and testing services through the grouting process.

Approach

• MoDOT called on GeoEngineers for its recognized expertise in geophysical, geological and geotechnical work.
• GeoEngineers obtained five electrical resistivity tomography (ERT) profiles in the immediate vicinity of the bridge’s foundation that concerned MoDOT, sending electrical current through 74 electrodes placed on the ground surface to provide a two-dimensional view of the subsurface.
• With the geotechnical information provided by MoDOT and the geophysical data, GeoEngineers provided geological consultation on the project.
• GeoEngineers provided onsite construction monitoring, including detailed daily field reports and strength and quality testing of grouting materials. This work documented the quality of the grout materials used on site, grout placement and minor lifting of the bridge during grouting operation.

Results

• GeoEngineers acted immediately to help MoDOT complete this important project in as little time as possible—addressing public safety concerns while reducing Interstate traffic delays caused by the bridge closure.
• With GeoEngineers’ geophysical exploration added to geotechnical data, MoDOT could be confident with the analysis of what lay beneath the Gasconade River Bridge foundation.
• GeoEngineers’ onsite construction observation and testing of grouting materials assured the project proceeded according to MoDOT’s plans and specifications.