BACKGROUND: Current methods for predicting local scour at bridge piers, including those described in Hydraulic Engineering Circular No. 18 (Publication No. FHWA NHI 01-001, "Evaluating Scour at Bridges"), were developed on the basis of small-scale laboratory studies and do not consider factors relevant to wide piers and long skewed piers. Because of these limitations, the current methods generally over-predict local scour at such piers, leading to the use of unwarranted and costly foundations or countermeasures. There is a need for research to evaluate current methods for predicting local pier scour and their applicability to wide piers and long skewed piers and to develop improved methods for use by highway agencies in the design, operation, and maintenance of highway bridges.
OBJECTIVE: The objective of this research is to develop methods and procedures for predicting time-dependent local scour at wide piers and at long skewed piers, suitable for consideration and adoption by AASHTO. The research shall be limited to non-cohesive soils and steady flow.
TASKS: Accomplishment of this objective will require at least the following tasks.
Phase I: (1) Collect and review information on time-dependent and equilibrium local scour around piers. This information may be obtained from domestic and foreign literature, contacts with public and private agencies and industry organizations, and other sources. (2) Based on the information gathered in Task 1, identify and assess the adequacy of available methods to predict time-dependent local scour at wide piers and at long skewed piers. Identify the sources and availability of laboratory and field data that could be used in this research to develop improved prediction methods. Also, identify existing and planned instrumented sites that could be used for field verification of prediction methods. (Note: The approach and process recommended for the assessment of available methods must be described in detail. While candidate field sites shall be identified in this task, field studies using these sites are not envisioned as part of this project; such studies may be considered in another project). (3) Based on the assessment performed in Task 2, refine the work plan for developing improved or new prediction methods to ensure that it will address the deficiencies of available methods. (Note: The refined work plan must provide detail regarding the work anticipated in Phases II. The work proposed for each task must be divided into subtasks, and the wotk proposed for each subtask must be described in detail. The proposed research plan shall include details of any proposed laboratory and field studies. Consideration should be given to time-dependent effects of complex pier geometry compared with equivalent simple piers, and to scale effects). (4) Prepare an interim report that documents the research performed in Tasks 1 and 2 and includes the updated work plan for Phase II. Following review of the interim report by the panel, the research team will meet with the project panel. Work on Phase II of the project will not begin until the interim report is approved and the updated work plan is authorized by the NCHRP.
Phase II: (5) Obtain, and evaluate the reliability of, the laboratory and field data identified in Task 2, and extract the data that are suited for use in developing improved prediction methods. (6) Using the data extracted in Task 5, execute the plan approved in Task 4, and develop improved methods and procedures for predicting time-dependent local pier scour. For several scenarios, compare the predictions from these methods and other methods identified in Phase I to the laboratory and field data acquired in Task 5, and discuss the accuracy of these predictions. (7) Based on the results of previous work, develop a research plan for the laboratory investigations (and other appropriate investigations) that are needed for further refinement of the developed methods and procedures and may be performed in follow up research efforts. (8) Submit a final report that documents the entire research effort. The developed methodology and procedures shall be prepared as an appendix for use by hydraulic engineers and shall be presented in a format appropriate for consideration and adoption by AASHTO or other agencies.
Status: Work is progressing on Phase II; a preliminary draft final report is expected in late January 2010.
Product Availability: No products are currently available.
