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CONTENTS Page No. FIGURESâ¦â¦â¦â¦â¦â¦..â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.iii TABLESâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦vi SYMBOLSâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦vii AUTHOR ACKNOWLEDGMENTSâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ix ABSTRACTâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦x EXECUTIVE SUMMARYâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... 1 CHAPTER 1. INTRODUCTIONâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 9 1.1 Definitionsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... 9 1.2 Motivation for Reviewâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... 10 1.3 Objectivesâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦...14 1.4 Approachâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 14 CHAPTER 2. ABUTMENT FORM AND CONSTRUCTIONâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦...15 2.1 Abutment Formâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 15 2.2 Abutment Layoutâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦16 2.3 Abutment Constructionâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 17 2.4 Pier Proximityâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 19 2.5 Sediment and Soil Boundary Materialâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦20 2.6 Flow Fieldâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 21 CHAPTER 3. ABUTMENT SCOUR AS A DESIGN CONCERNâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 25 3.1 Design Scour Depthsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 25 3.2 Estimation of Scour Depthsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦25 3.3 An Essential Design Questionâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦26 CHAPTER 4. SCOUR CONDITIONSâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦28 4.1 Three Common Conditions of Abutment Scourâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 28 4.2 Influence of Pier Proximityâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 32 4.3 Other Scour Processesâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦32 CHAPTER 5. ABUTMENT SCOUR DEPTH ESTIMATION FORMULASâ¦â¦â¦â¦â¦â¦ 34 5.1 Parameter Frameworkâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 34 5.2 Summary of Abutment Scour Formulasâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 37 5.3 Classification of Scour Formulasâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... 42 5.4 Evaluation of Abutment Scour Formulasâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦...48 5.5 Geotechnical Approachâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 58
ii CHAPTER 6. CONTRACTION SCOUR FORMULASâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 60 6.1 Definition of Contraction Scourâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.60 6.2 Dimensional Analysisâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 60 6.3 Idealized Long-Contraction Scourâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 62 6.4 Contraction Scour Formulas from Laboratory Dataâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 63 6.5 Field Data on Contraction Scourâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦64 6.6 Vertical Contraction Scourâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.65 CHAPTER 7. RECOMMENDATIONS FOR DESIGN ESTIMATION OF ABUTMENT AND CONTRACTION SCOURâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..66 7.1 General Recommendationsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.66 7.2 Specific Recommendationsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 67 CHAPTER 8. RESEARCH AND EDUCATION NEEDSâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..70 8.1 Introductionâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 70 8.2 Scour Processesâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 70 8.3 Design Estimation of Scourâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦71 8.4 Monitoring and Maintenanceâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 73 CHAPTER 9. CONCLUSIONSâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦...75 CHAPTER 10. REFERENCESâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦78 APPENDICES A. Abutment Scour Equationsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 83 B. Contraction Scour Equationsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... 85 C. Research Problem Statementsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..87
iii FIGURES Caption Page No. Figure 1-1. Schematic of long, multi-span bridge over a compound channelâ¦â¦â¦â¦â¦â¦. 11 Figure 1-2. Schematic of relatively short bridge over narrow main channel â¦â¦â¦â¦â¦â¦.. 11 Figure 1-3. Abutment scour resulting in embankment failure by collapse due to geotechnical instabilityâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..12 Figure 1-4. Scour at I-70 bridge over Missouri River from 1993 flood with flow from left to right. (Photo from Parola et al. 1998)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 13 Figure 2-1. Plan views of the two common abutment forms: (a) Wing-wall; (b) Spill-through (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 15 Figure 2-2. Definitions of embankment length, floodplain width, and main channel width (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 16 Figure 2-3. Isometric view of spill-through abutment comprising a standard-stub column located within the end of an earthfill embankment (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦. 17 Figure 2-4. The geometry and dimensions of a standard-stub abutment commonly used for spill-through abutments (prototype scale indicated); design provided by the Iowa DOT (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 18 Figure 2-5. The geometry and dimensions of a wing-wall abutment - compacted earthfill embankment extends back from the abutment structure (prototype scale indicated); design provided by the Iowa DOT (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..18 Figure 2-6. A spill-through abutment with a pier in close proximity; approximate layout proportions of L/Bf = 1.0; Bf/0.5B â 0.7, and L/W â 1.0, in which W = embankment top width (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 19 Figure 2-7. Variation of soil and sediment types at a bridge crossing (Ettema et al. 2010)â¦.20 Figure 2-8. Flow structure including macro-turbulence generated by flow around abutments in a narrow main channel. (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 21 Figure 2-9. Flow structure including macro-turbulence generated by floodplain/main channel flow interaction, flow separation around abutment, and wake region on the floodplain of a compound channel. (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..22
iv Caption Page No. Figure 2-10. Interaction of flow features causing scour and erodibility of boundary (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 23 Figure 2-11. For a spill-through abutment well set back on a flood-plain, deepest scour usually occurs where flow is most contracted through the bridge waterwayâ¦â¦â¦â¦â¦â¦.. 24 Figure 3-1. A common situation of abutment failure; scour has led to failure and partial washout of the earthfill spill-slope at this abutment. A basic question arises as to how abutment design should take scour into accountâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..27 Figure 3-2. Failure of abutment fill in September 2009 Georgia flood accompanied by failure of approach roadway (Hong and Sturm 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 27 Figure 4-1. Abutment-scour conditions: Scour Condition A - hydraulic scour of the main channel bed causes bank failure, which causes a failure of the face of the abutment embankment (a); Scour Condition B - hydraulic scour of the floodplain causes failure of the face of the abutment embankment (b); and, Scour Condition C - breaching of the approach embankment exposes the abutment column so that scour progresses as if the abutment were a form of pier (c) (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 29 Figure 4-2. Field example of Scour Condition Aâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦31 Figure 4-3. Scour Condition Bâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 31 Figure 4-4. Scour condition C for a wing-wall abutmentâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.32 Figure 5-1. Definition sketch for abutment terminating in a compound channelâ¦â¦â¦â¦â¦.35 Figure 5-2. Bankline abutment in a narrow channelâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 45 Figure 5-3. Bridge crossing for a compound channelâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 45 Figure 5-4. Bridge crossing of a braided channelâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ 46 Figure 5-5. Comparison between scour data at a spill-through abutment (with riprap protection extended below the surface of the floodplain) and the formula by Sturm and Chrisochoides 1998 (see also Sturm 2004, 2006). Reproduced from NCHRP Report 587 by Barkdoll et al. (2007)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 52 Figure 5-6. Comparison between scour data at a spill-through abutment (with riprap protection extended below the surface of the floodplain) and the formula by Melville (1997). Reproduced from NCHRP Report 587 by Barkdoll et al. (2007)â¦â¦â¦â¦.52
v Caption Page No. Figure 5-7. Comparison of Briaud et al. (2009) formula with experimental results of Ettema et al. (2010) for Scour Condition B. [Reproduced from Briaud et al. (2009). Final design curves are Figs. 12.3 and 12.4 of the NCHRP 24-20 report by Ettema et al. (2010)]â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.54 Figure 5-8. Comparison of Melville (1992, 1997) formula and Sturm (2004, 2006) data for rigid abutments with Ettema et al. (2010) data for erodible abutments and Scour Condition Bâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 55 Figure 5-9. Scour depth trends for Scour Condition B. (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦...56 Figure 5-10. Minnesota River near Belle Plaine, MN for 2001 flood. (Wagner et al. 2006)...57 Figure 5-11. Scour depth estimation based on geotechnical stability of embankment; (a) variables, (b) failure of embankment past abutment column relieves flow so that maximum scour depth is attained (Ettema et al. 2010)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦..59 Figure 6-1. Definition sketch for idealized long contraction scour (Q1 = main channel flowrate for live-bed scour; Q2 = total flowrate in channel at contracted section; dsc = contraction scour depthâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 61
vi TABLES Caption Page No. Table 5-1. Classification of abutment scour parametersâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.. 36 Table 5-2. Formulas categorized by parameter groupsâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦... 43 Table 5-3. Limitations and experimental databases of abutment scour formulaâ¦â¦â¦â¦â¦. 50 Table 8-1. Prioritized list of research and education needs addressing improved understanding of abutment-scour processesâ¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.71 Table 8-2. List of design-related research tasks addressing improved design estimation of abutment scour depth coupled to research needs in Table 8-1â¦â¦â¦â¦â¦â¦...73 Table 8-3. Prioritized list of research and education needs addressing improved methods for monitoring and maintenance (needs I1, I2, and I3 can be combined)â¦â¦â¦â¦..74 Table A-1. A selection of abutment scour equations (revised and extended from Melville and Coleman 2000)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦.83 Table B-1. A selection of contraction scour formulas (B1 = approach flow channel width; B2 = contracted channel width; Y1 = approach flow channel depth; Y2 = contracted channel depth after scour)â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦. 85
vii SYMBOLS B = width of total flow cross section at the bridge crossing Bf = width of the floodplain Bm1 = width of the main channel in the approach flow section Bm2 = width of the main channel in the bridge section ds = scour depth at the bridge section d = some measure of the sediment size such as the median size by weight, d50 F = flow Froude number Fc = critical flow Froude number when sediment motion begins Fd = densimetric grain Froude number = V / [(Ïs/Ïâ1)gd]1/2 g = acceleration of gravity HE = height of the embankment kF = roughness height of the floodplain km = roughness height of the main channel Ks = shape factor of the abutment as it affects scour by the flow field Kθ = embankment skewness factor as it affects scour Kf = spiral flow factor in Maryland formula Kv = velocity adjustment factor in Maryland formula Kp = pressure flow coefficient in Maryland formula L = length of the abutment/embankment Lc = length of contraction transition m = geometric contraction ratio = (B â 2L)/L M = discharge contraction ratio = (Q â Qobst) /Q Q = total discharge going through the bridge Qobst = discharge in the approach flow obstructed by the bridge embankment q1 = discharge per unit width in approach flow cross section q2 = discharge per unit width in contracted bridge section u*1 = shear velocity of the approach flow u*c = critical value of shear velocity for initiation of sediment motion V1 = approach flow velocity Vc = critical velocity for initiation of sediment motion W = width of the embankment in the flow direction Y1 = upstream approach flow depth in main channel Y2 = maximum depth of flow after scour at the bridge in main channel or floodplain YC = mean flow depth at the bridge due to contraction scour YF = upstream approach flow depth in the floodplain YMAX = maximum flow depth at the bridge after scour Greek symbols α = scour amplification factor Ï = density of the fluid Ïs = sediment density µ = viscosity of the fluid, respectively Ïg = geometric standard deviation of grain size distribution Ï = bulk shear strength of the embankment fill
viii γE = bulk density of the embankment Ï1 = mean boundary shear stress in approach flow Ï2 = mean boundary shear stress in contracted flow section Ïc = critical shear stress for initiation of sediment motion