Drilled Shaft Value Engineering Delivers Success to Wahoo, Nebraska Bridge

This case history illustrates how a successful "Value Engineering" redesign with slurry-drilled shafts and an O-Cell test saved considerable costs and expedited early completion of a large bridge project for the Nebraska Department of Roads (NDOR). The paper first describes the original project and its geologic setting. It then relates the inception, development and verification of the redesign concept and its implementation via NDOR's "Value Engineering Proposal" (VEP) standard specification provisions. The comparative advantages of drilled shafts versus driven piles relative to the site geology, some benefits of using polymer drilling slurry and the practicality of foundation verification with an O-Cell test and cross-hole sonic logging (CSL) are discussed. The lack of redundancy in drilled shafts and the increased importance of having an experienced contractor using appropriate equipment and procedures under an effective quality control program are also emphasized. The paper concludes with a discussion of the overall impact of the VEP redesign on the project cost and schedule, as well as on NDOR's subsequent bridge design and construction practices.