Scour is the result of the erosive action of flowing water, entraining and removing boundary material from channel beds and/or banks and around bridge foundations. In gravel-bed rivers the interaction of the heterogeneous, large gravel particles with the approaching flow can generate coherent turbulent structures in the flow. In addition to increasing the shear stress applied by the flow onto the bed, these structures create a highly variable bed shear stress field increasing the gravel-bed mobility (Tsakiris et al., 2014; Sarkar et al., 2016), compromising bridge foundation integrity.
The majority of the formulas used in current engineering practice for predicting scour depth around bridge foundations have been developed for sand-bed rivers, which are characterized by near-uniform bed material (Dey and Raikar, 2005; Ettema et al., 2011; Guo et al., 2012; Manes and Brocchini, 2015). As a result, parameters such as the heterogeneity of bed material have been excluded from their formulations, and the empirical coefficients appearing in these formulas have been derived from laboratory experiments conducted with near uniform sand-sized sediment. Due to these limitations, when applied in gravel-bed rivers, these formulas significantly overestimate the scour depth (Dey and Raikar, 2005; Holnbeck, 2011).
Recognizing the shortcomings of current scour prediction methodologies, researchers have attempted to include the effects of gravel particle heterogeneity using empirically derived correction coefficients. However, the failure of existing scour prediction methodologies to fundamentally account for the unique characteristics of gravel-bed
rivers translates to significant scour depth prediction errors, even after correction.
Development of a scour prediction methodology that accounts for gravel-bed rivers will be valuable for bridge owners and practicing engineers and will provide more accurate predictions of the scour depth.
The objective of this research is to develop a rigorously tested and rapidly deployable methodology for bridge owners that will accurately predict scour at new bridge foundations and evaluate scour at existing bridge foundations in gravel-bed rivers by (1) providing reliable data for fluid-induced forces, required to generate incipient motion in the surface and subsurface layers of gravel-bed rivers; and (2) combining fluid-induced erosion forces, and incipient motion data to predict scour depths at bridge foundations with gravel-bed rivers that have ¼ inch gravel to 12 inch cobble mixtures with varying sand content up to 20%.
The NCHRP is seeking the insights of proposers on how best to achieve the research objective. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objective.
The research objective may be attained through some combination of critical literature review, modeling, experimental work, and/or field investigation. The research team should propose a logical research plan and detailed tasks to accomplish the research objective within the project duration and budget. All proposed approaches must be justified and limitations clearly stated. The methodology must be validated and its reliability demonstrated using a combination of literature, field, modeling, and laboratory data. The research plan must identify appropriate milestones and interim deliverables. The proposal must show how the research team’s collective expertise is able to utilize innovative approaches to accomplish the research objective.
The research plan should: (1) include a kick-off teleconference with the research team and NCHRP convened within 1 month of the contract’s execution; (2) address the manner in which the proposer intends to satisfy the project objective; (3) include one face-to-face meeting to review the findings from an interim report, and a web-conference meeting (NCHRP will provide teleconference services) to be held at a logical point in the project schedule; and (4) incorporate opportunities for the project panel to review, comment and approve milestone deliverables.
Note: Following receipt of the draft final deliverables, the remaining 3 months shall be for NCHRP review and comment and for research agency preparation of the final deliverables.
Final deliverables should include, at a minimum: (1) a final report that documents the new scour depth prediction method, and details its development, range of applicability, and the data requirements for immediate use by bridge owners; (2) at least one case study illustrating the use and step-by-step computational procedures and application of the new methodology; (3) an executive summary of the project; (4) recommendations for incorporation into the current scour design methods; (5) a PowerPoint presentation describing the background, objectives, research approach, findings, and conclusions; (6) presentation of findings at the National Hydraulic Engineering Conference and one meeting of the AASHTO Program Delivery and Operations or Cross Discipline Committee; and (7) a stand-alone technical memorandum titled “Implementation of Research Findings and Products” (see Special Note D for additional information).
Proposers may recommend additional deliverables to support the project objective.
A. Research team should have familiarity with current and pending FHWA scour design methodologies (e.g., HEC-18, HEC-20, and HEC-23).
Note: Please see the FHWA-Scour Depth Limit State Design Approach for the pending FHWA scour design methodology.
B. Research team should have multidisciplinary expertise.
C. Item 4 of the proposal, the research plan, shall not exceed 16 pages excluding references. This does not include the detailed schedule or the detailed budget. Item 5 of the proposal shall be limited to 2 pages of biographical information for each person.
D. Proposals should include a task-by-task breakdown of labor hours for each staff member as shown in Figure 4 in the brochure, "Information and Instructions for Preparing Proposals" (http://onlinepubs.trb.org/onlinepubs/crp/docs/ProposalPrep.pdf). Proposals also should include a breakdown of all costs (e.g., wages, indirect costs, travel, materials, and total) for each task using Figures 5 and 6 in the brochure. Please note that TRB Cooperative Research Program sub awards (selected proposers are considered sub awards to the National Academy of Sciences, the parent organization of TRB) must comply with 2 CFR 200 – Uniform Administrative Requirements, Cost Principles, and Audit Requirements for Federal Awards. These requirements include a provision that proposers without a "federally" Negotiated Indirect Costs Rate Agreement (NICRA) shall be subject to a maximum allowable indirect rate of 10% of Modified Total Direct Costs. Modified Total Direct Costs include all salaries and wages, applicable fringe benefits, materials and supplies, services, travel, and up to the first $25,000 of each lower-tier sub award and subcontract. Modified Total Direct Costs exclude equipment, capital expenditures, charges for patient care, rental costs, tuition remission, scholarships and fellowships, participant support costs and the portion of each lower-tier sub award and subcontract in excess of $25,000.
E. NCHRP wishes to award NCHRP Project 24-48 for a fixed price of $600,000. This amount will not be subject to any adjustment by reason of the contractor’s cost experience in the performance of the award. In addition to providing a detailed budget, the proposer should provide a proposed schedule of project milestones, deliverables, and progress payments tied to the detailed budget and schedule. For budgeting purposes, proposers should assume that (1) NCHRP will provide access to web-enabled teleconference services and (2) 1 in-person meeting with the NCHRP project panel will be held in Washington, DC. NCHRP will pay panel members’ travel costs for the meeting.
F. The NCHRP is a practical, applied research program that produces implementable products addressing problems faced by transportation practitioners and managers. The benefits of NCHRP research are realized only when the results are implemented in state DOTs and other agencies. Implementation of the research product must be considered throughout the process, from problem statement development to research contract and beyond completion of the research. Item 4(c), "Anticipated Research Results," must include the following: (a) the "product" expected from the research, (b) the audience or "market" for this product, (c) a realistic assessment of impediments to successful implementation, and (d) the institutions and individuals who might take leadership in deploying the research product. The project panel will develop and maintain an implementation plan throughout the life of the project. The research team will be expected to provide input to an implementation team consisting of panel members, AASHTO committee members, the NCHRP Implementation Coordinator, and others in order to meet the goals of NCHRP Active Implementation: Moving Research into Practice, available at http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP_ActiveImplementation.pdf.
G. Item 5 in the proposal, "Qualifications of the Research Team," must include a section labeled "Disclosure." Information relevant to the NCHRP's need to ensure objectivity and to be aware of possible sources of significant financial or organizational conflict of interest in conducting the research must be presented in this section of the proposal. For example, under certain conditions, ownership of the proposing agency, other organizational relationships, or proprietary rights and interests could be perceived as jeopardizing an objective approach to the research effort, and proposers are asked to disclose any such circumstances and to explain how they will be accounted for in this study. If there are no issues related to objectivity, this should be stated.
H. Proposals are evaluated by the NCHRP staff and project panels consisting of individuals collectively very knowledgeable in the problem area. Selection of an agency is made by the project panel considering the following factors: (1) the proposer's demonstrated understanding of the problem; (2) the merit of the proposed research approach and experiment design; (3) the experience, qualifications, and objectivity of the research team in the same or closely related problem area; (4) the plan for ensuring application of results; (5) the proposer's plan for participation by Disadvantaged Business Enterprises--small firms owned and controlled by minorities or women; and (6) the adequacy of the facilities.
Note: The proposer's plan for participation by Disadvantaged Business Enterprises should be incorporated in Item 12 of the proposal.
I. Copyrights - All data, written materials, computer software, graphic and photographic images, and other information prepared under the contract and the copyrights therein shall be owned by the National Academies of Sciences, Engineering, and Medicine. The contractor and subcontractors will be able to publish this material for non-commercial purposes, for internal use, or to further academic research or studies with permission from TRB Cooperative Research Programs. The contractor and subcontractors will not be allowed to sell the project material without prior approval by the National Academies of Sciences, Engineering, and Medicine. By signing a contract with the National Academy of Sciences, contractors accept legal responsibility for any copyright infringement that may exist in work done for TRB. Contractors are therefore responsible for obtaining all necessary permissions for use of copyrighted material in TRB's Cooperative Research Programs publications. For guidance on TRB's policies on using copyrighted material please consult Section 5.4, "Use of Copyrighted Material," in the Procedural Manual for Contractors.