Technical Support for SDDOT's Pile Load Testing

In response to the Federal Highway Administration’s October 1, 2007 deadline that applies to all federally funded bridge projects, the South Dakota Department of Transportation (SDDOT) has transitioned to Load and Resistance Factor Design (LRFD) Specifications. Load and resistance factor design methods, including the American Association of State Highway & Transportation Officials (AASHTO) LRFD Specifications, are based on limit state design, which uses load and resistance factors to account for a factor of safety. They rely heavily on statistical probability and reliability theories. LRFD differs from traditional allowable stress design (ASD) analysis, which is based on a global factor of safety. Research project SD2008-08, Review and Refinement of SDDOT’s LRFD Deep Foundation Design Method, involved a comprehensive review of deep foundation design procedures at SDDOT to identify potential improvements in design efficiency and reliability. The project elevated awareness of the LRFD transition process and goals, emphasized the importance of updating current deep bridge foundation design procedures, and identified potential improvements in SDDOT’s overall design process. Researchers verified that SDDOT is in compliance with the Federal Highway Administration’s mandate regarding deep foundation design of driven H-pile sections, precast concrete, timber piles, and drilled shafts. In the course of the SD2008-08 study, it became apparent that available pile load test data is not sufficient to verify SDDOT’s current predictive design method or reliably determine resistance factors specific to conditions in South Dakota. The formal implementation plan for SD2008-08 proposes a focused, five-year program of pile load testing within regular construction projects to supplement the existing load test database. This research is necessary to provide technical support for the load testing and to analyze load test data to verify and improve accuracy of resistance factors and predictions of pile drivability and bearing capacity. The research objectives are to: (1) Support pile load testing, data analysis, verification of pile driveability and bearing capacity formulas, and recalibration of resistance factors for deep foundation design. (2) Recommend further refinements to SDDOT’s current foundation design procedures consistent with LRFD Specifications. (3) Assist SDDOT with expanded use of LRFD Specifications to optimize reliability, consistency, and efficiency of deep foundation designs.