BACKGROUND

Scour has a major effect on the design, construction, and maintenance costs of bridges. Improving the understanding of the interaction between pier, contraction, and abutment scour is key to safe and cost-effective design of foundations. The interaction between pier, contraction, and abutment scour; its effects on bed shear stresses; and the resulting depth and extent of their collective impact is a topic with limited study. The current practice is to estimate the scour components separately and compute the total scour as the sum of the individual components. This practice can lead to the overestimation of scour potential, thereby causing an increase in design, construction, and maintenance costs. 

Research is needed to assist state departments of transportation (DOTs) in understanding the interaction between scour types and which scour types control overbank and channel scour potential. This research would include the study of total scour from a system perspective and the development of scour profile guidance.

OBJECTIVE

The objective of this research is to develop procedures for determining the interaction of pier, contraction, and abutment scour components and their contributions to the total scour potential. The procedures must be rational, properly structured, well documented, comprehensive, logical, and practical for use by state DOT engineers and other practitioners.   

Accomplishment of the project objective will require at least the following tasks.

TASKS

PHASE I—Planning

Task 1. Conduct a literature review of research and the state-of-practice on the interaction of scour components (pier, contraction, and abutment), determination of total scour, and scour profile development. The review shall include published and unpublished documentation, past surveys, and research conducted through the NCHRP; Federal Highway Administration; and other national, state, and pooled-fund sponsored research. 

Task 2. Synthesize the results of the literature review to identify knowledge gaps related to the research objective. These gaps should be addressed in the final product or the recommended future research, as budget permits.

Task 3. Propose a research plan to be executed in Phase II to achieve the research objective. At a minimum, the research plan shall include:

• A scientific, physics-based approach (e.g., flume studies, computational fluid dynamics models) for investigating bed shear stresses and resulting scour depths for (1) the individual scour components, (2) the interaction between contraction scour and pier scour, and (3) the interaction between all scour components within the abutment scour region; 
• Cases for a single column pier and pile bent; 
• Testing matrix with varying hydraulic and geometric parameters; 
• A phased testing approach; and
• Coordination with the U.S. Geological Survey (USGS), state DOTs, or any other entities to locate existing scour field survey data. If necessary, conduct scour field surveys at additional sites with characteristics outside of available data set. Include sites with historical hydraulic and subsurface soil data. This data will be used as verification data for the flume and computational fluid dynamics studies.

Task 4. Prepare Interim Report No. 1 that documents Tasks 1 through 3 and provides an updated work plan for the remainder of the research. The updated plan must describe the process and rationale for the work proposed for Phases II and III.

PHASE II—Execution

Task 5. Execute the research plan according to the approved Interim Report No. 1.

Task 6. Develop draft procedures for determining the interaction of pier, contraction, and abutment scour components and their contributions to the total scour potential.  

Task 7. Prepare Interim Report No. 2 that documents Tasks 5 and 6 and provides an updated work plan for the remainder of the research. The updated work plan must describe the process and rationale for the work proposed for Phase III.

PHASE III—Final Products

Task 8. Revise the proposed procedures described in Task 6 after consideration of the panel’s review comments.

Task 9. Submit the final deliverables including:

• The procedures for determining the interaction of pier, contraction, and abutment scour components and their contributions to the total scour potential;
• A final report that documents the entire research effort;
• Database containing all field data collected in an Excel format; and
• A stand-alone technical memorandum titled “Implementation of Research Findings and Products.”
  

STATUS: A research agency has been selected for the project. The contracting process is underway.