Landslide at a Bridge Abutment in St. Louis, Missouri

The Missouri Department of Transportation (MoDOT) is currently reconstructing Interstate 70 through the City of St. Louis. As part of the reconstruction, numerous bridges are being replaced. The O'Fallon Park Drive Overpass was nearing completion in the Spring of 2002 when movement was observed in the slope adjacent to the southern bridge abutment. A geotechnical investigation was performed to characterize the subsurface conditions and evaluate the cause of the slide. Slope mitigation measures consisted of a multi-staged approach. As an interim repair, pipe aggregate drains (similar to french drains) were installed in the slope to intercept groundwater flowing downhill toward and within the slide mass. The final repair consists of a tied-back tangent pile wall and a rock shear key. The tangent pile wall consists of drilled shafts installed to bedrock connected with a grade beam beneath the new bridge. The grade beam contains tiebacks installed into the underlying bedrock. A rock-filled shear key with a drainage pipe will be constructed in the slope east of the new bridge.