Evaluation of Pile Setup from Osterberg Cell Load Tests and Its Cost–Benefit Analysis

Abstract

Results are presented of Osterberg cell load tests (OCLTs) that were performed over a 2-year period to measure setup (increase in pile resistance with time) on a 30-in. prestressed concrete test pile at the Bayou Boeuf Bridge site in Louisiana. The test pile was instrumented with vibrating wire strain gauges to evaluate the load distribution along the pile length during the OCLTs. An Osterberg cell was installed at the tip of the pile. A series of dynamic load tests and five OCLTs was performed to measure the amount of setup from end of driving over a 2-year period. The load test results showed that setup was attributed mainly to the increase in side resistance with time, while the tip resistance remained almost constant. In this study, setup was analyzed for individual soil layers instead of total pile resistance; hence the effect of soil properties on setup behavior was evaluated. This long-duration setup study demonstrated the effect of consolidation and aging on setup behavior. The side resistance increased by 380% compared with the end-of-driving side resistance over the 2 years. The study showed that the long-term pile side resistance was 28% higher than the 14-day pile side resistance. A cost analysis was performed to determine the potential savings of including pile setup in the project. With use of long-term pile resistance, a 13% reduction in pile length for 566 piles could be made, yielding a cost savings of about $600,000.