Review and Refinement of SDDOT's LRFD Deep Foundation Design Method

Advances in materials science and soil mechanics, as well as evolving traffic patterns and public perceptions have prompted a nationwide push to update bridge foundation/substructure design methods. In response to the Federal Highway Administration's October 1, 2007 deadline that applies to all federally funded bridge projects, the SDDOT has moved ahead with transitioning to new Load Resistance Factor Design (LRFD) Specifications. Load resistance factor design models 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. This differs from traditional allowable stress design (ASD) geotechnical engineering analysis, which is based on a global factor of safety. South Dakota Department of Transportation's (SDDOT's) current "calibration-to-fit" design parameters for deep foundations need to be reviewed and refined by determining geotechnical resistance factors for conditions specific to South Dakota. Existing data needs to be compiled and analyzed to generate the enhanced input parameters. The objectives of this research project as to: (1) assess the current status of Federal Highway Administration (FHWA) sanctioned LRFD Specifications as they pertain to SDDOT foundation design procedures; (2) recommend refinements to SDDOT's current foundation design procedures consistent with LRFD Specifications; and (3) assist SDDOT with expanded use of LRFD Specifications in an effort to optimize reliability, consistency, and efficiency. Research tasks of the project are as follows: (1) Meet with the project's technical panel to review the project scope and work plan. (2) Conduct interviews with key SDDOT stakeholders to review SDDOT deep foundation design methodology including; field testing procedures, lab testing procedures, sampling procedures, selection of pile materials, and pile driving formulas. (3) Provide detailed information on FHWA requirements for LRFD resistance values. (4) Review and evaluate approaches used by neighboring states (MN, ND, WY, NE, MT, & IA) related to LRFD implementation and identify opportunities where their application may benefit SDDOT methodology. (5) Review SDDOT's current methods for determining resistance factors used in deep foundation design and assess their application to calibration of LRFD resistance factors. (6) Meet with the Technical Panel to review and approve interim results and to confirm project direction. (7) Assemble a database of applicable field data, including load test or pile driveability analysis data, available from SDDOT, local contractors, consultants, and neighboring state transportation departments. (8) Analyze available load test data for resistance values and factors and compare to current SDDOT load capacity prediction methods. (9) Attempt probabilistic analysis of available project field data to calibrate resistance factors specific to South Dakota. This task will depend upon the amount and quality of the data obtained in Task 7 and Task 8. If the amount or quality of the data is deemed insufficient for a probabilistic analysis, recommendations will be made regarding advancing the load test and pile driveability database for calibration of resistance factors in the future. (10) Make recommendations for a specific approach for instituting LRFD and acquisition of data in support of the selected approach. (11) Meet with the technical panel to review and accept results of the investigation and proposed recommendations. Identify an appropriate project with sufficient parallel analysis to demonstrate application of LRFD principles. (12) Provide on-site technical support to SDDOT in applying LRFD resistance values and factors to deep foundation design, including a demonstration using parallel data from a suitable project to facilitate application of concepts on paper. If the probabilistic analysis for Task 9 is not possible, review of SDDOT foundation design procedures with respect to an acceptable LRFD approach will be conducted. Technical support and/or recommendations will be provided to SDDOT to implement the code specified resistance factors from an acceptable LRFD manual in lieu of resistance factors specific to South Dakota. (13) Prepare a final report and executive summary of project results, findings, conclusions, and recommendations including: opportunities for optimization of current practices; potential impacts to existing field, lab and design procedures; qualifying perceived efficiencies; and detailed proposal to assist SDDOT with application of advanced LRFD principles to deep foundation design. (14) Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.