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OCR for page 105
105 Future Hydrograph Table 12.5 and Figures 12.20 through 12.26 provide a sum- 14000 mary of input data and illustrate the results. 12000 12.6 EXAMPLE 6: BRIDGE WITH GROUP PIERS 10000 Discharge (m /sec) AND CONTRACTED CHANNEL WITH HYDROGRAPH IN CONTRACTED 3 8000 SECTION 6000 Given: 4000 Pier geometry: Pier width B = 1.52 m, pier length Lpier = 12.19 m, rectangular pier, num- 2000 ber of piers, N = 6, spacing, S = 30 m Channel geometry: Upstream uncontracted channel width 0 B1 = 725 m, contracted channel width 0 10 20 30 40 50 60 70 Time (Year) due to bridge abutment B2 = 122 m, Contraction length of channel L: = Figure 12.20. Seventy years future approaching 40 m hydrograph (Example 5). EFA Result (Layer 1) 20 18 Scour rate Shear stress 16 (mm/hr) (N/m2) 14 0 1 Scour Rate (mm/hr) 1 4 12 2 6 10 3 9 6 30 8 10 100 6 12.5 200 16 400 4 2 0 01 00 2003 00 400 2 Shear Stress (N/m ) Figure 12.21. EFA results for Soil Layer 1 (Example 5). EFA Result (Layer 2) 8 7 Scour rate Shear stress (mm/hr) (N/m2) 6 0 3 Scour Rate (mm/hr) 5 0.1 4 1 6 4 2 9 4 18.5 3 5 27 2 6 40 6.9 60 1 0 01 02 03 04 05 06 07 0 2 Shear Stress (N/m ) Figure 12.22. EFA results for Soil Layer 2 (Example 5).

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106 V1 Abutment River Bank Flow River Bank transition angle: 90 degrees Flow parameters: 70 years predicted hydrograph Manning B1 Coefficient: 0.0146 Hydraulic radius: 2.62 m EFA result: Layer 1: Thickness 15 m; critical shear 60 stress 2 N/m2 Layer 2: Thickness 20 m; critical shear B2 stress 4 N/m2 L Flood period: 70 years Determine: The magnitude of maximum bridge Bridge Abutment Bridge Abutment scour depth 12.6.1 SRICOS-EFA Method: Computer Calculation Figure 12.23. Plan view of contracted channel scour case (Example 5). Since the hydrograph is used in this case as hydrologic data input, the relationship between the discharge and Discharge vs. Velocity Discharge vs. Water Depth 4.00 16.0 3.50 14.0 3.00 12.0 Water Depth (m) Velocity (m/s) 2.50 10.0 2.00 8.0 1.50 6.0 1.00 4.0 0.50 2.0 0.00 05 0001 0000 150002 0000 25000 0.0 05 0001 0000 150002 0000 25000 Discharge (m3/s) Di scharge (m3/s) Figure 12.24. Relationship of discharge versus velocity and discharge versus water depth (Example 5). Maximum Contraction Scour Depth vs. Time Uniform Contraction Scour Depth vs. Time (Example 5) (Example 5) 10000 7000 9000 6000 8000 Pier Scour Depth (mm) Pier Scour Depth (mm) 7000 5000 6000 4000 5000 4000 3000 3000 2000 2000 1000 1000 0 0 Figure 12.25. Maximum contraction scour depth versus Figure 12.26. Uniform contraction scour depth versus time (Example 5). time (Example 5).

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107 TABLE 12.6 Summary of data input (Example 6) Input Unit SI 1 Output Unit SI 1 First Date of Analysis 01-01-2003 Last Date of Analysis 01-01-2073 No. Of Input Data 25569 Type of Pier Rectangular Pier 2 Pier Width 1.52 Pier Length 12.19 Attack angle 0 Number of piers 6 Pier spacing 30 Upstreamed Uncontracted Channel Width 725 Contracted Channel Width 122 Contraction Length of Channel 40 Transition Angle of Channel 90 Manning's Coefficient 0.0146 Average Hydraulic Radius 2.62 Time Step Hours 24 Type of Hydrologic Input Discharge 1 Type of Velocity Velocity in contracted section 2 Number of Regression Points Discharge vs. Velocity 8 1.42, 0 14, 0.02 141, 0.16 Input 566, 0.49 Hydrologic Values of Regression Discharge, Velocity 1415, 0.90 Data Points 5663, 2.50 12375, 4.20 19821, 5.60 Number of Regression Points Discharge vs. Water Depth 8 1.42, 3.86 14, 4.18 141, 5.02 Discharge, Water Depth Values of Regression 566, 6.18 Points 1415, 7.83 5663, 11.33 13592, 13.15 19821, 14.19 No. Of Layers 2 Properties of 1st Layer Thickness 15 Critical Shear Stress 2 Number of Regression Points Shear Stress vs. Scour Rate 8 1, 0 4, 1 Estimate Initial 6,2 Scour Rate Value of Regression Shear Stress, Scour Rate 9,3 Points 6, 30 100, 10 200, 12.5 400, 16 Properties of 2nd Layer Thickness 20 Critical Shear Stress 4 Number of Regression Points Shear Stress vs. Scour Rate 8 3, 0 4, 0.1 Estimate Initial 6,1 Scour Rate Value of Regression Shear Stress, Scour Rate 9,2 Points 18.5, 4 27, 5 40, 6 60, 6.9

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108 velocity and the relationship between discharge and water Future Hydrograph depth need to be defined. The HEC-RAS program can be 14000 a good tool to define these relationships. The follow- 12000 ing charts present the results obtained from HEC-RAS for this case. 10000 Discharge (m /sec) Use SRICOS-EFA program Option 3: Bridge Scour. 3 8000 6000 Results: After a 70-year period of flood, in this case the maximum 4000 final bridge scour is 2000 Z = 6.2 m 0 0 10 20 30 40 50 60 70 Time (Year) Table 12.6 and Figures 12.27 through 12.33 provide a sum- mary of input data and illustrate the results. Figure 12.27. Seventy years future hydrograph (Example 6). EFA Result (Layer 1) 20 18 16 14 Scour Rate (mm/hr) Scour rate Shear stress (mm/hr) (N/m2) 12 0 1 10 1 4 8 2 6 3 9 6 6 30 4 10 100 12.5 200 2 16 400 0 0 100 200 300 400 2 Shear Stress (N/m ) Figure 12.28. EFA results for Soil Layer 1 (Example 6). EFA Result (Layer 2) 8 7 Scour rate Shear stress (mm/hr) (N/m2) 6 Scour Rate (mm/hr) 0 3 5 0.1 4 1 6 4 2 9 4 18.5 3 5 27 2 6 40 6.9 60 1 0 0 10 20 30 40 50 60 70 2 Shear Stress (N/m ) Figure 12.29. EFA results for Soil Layer 2 (Example 6).

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109 8 7 6 Approach Cross Section Elevation, Meters 5 4 3 2 1 Left Overbank Main Channel Right Overbank 0 0 100 200 300 400 500 600 700 800 Distance, Meters Figure 12.30. Cross-section view of approaching channel (Example 6). 8 7 Bridge Cross Section 6 Elevation, Meters 5 4 3 2 1 30 m 30 m 30 m 30 m 30 m 0 300 350 400 450 Distance, Meters Figure 12.31. Cross-section view of bridge (Example 6).

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110 Discharge vs. Velocity (Contracted Section) Discharge vs. Water Depth 6.00 16.0 14.0 5.00 12.0 4.00 Velocity (m/s) 10.0 3.00 8.0 6.0 2.00 4.0 1.00 2.0 0.00 0.0 0 5000 10000 15000 20000 25000 0 5000 10000 15000 20000 25000 Discharge (m3/s) Discharge (m3/s) Figure 12.32. Relationship of discharge versus velocity and discharge versus water depth (Example 6). Scour Depth vs. Time (Example 6) 7000 6000 Pier Scour Depth (mm) 5000 4000 3000 2000 1000 0 0 10 20 30 40 50 60 70 Time (Year) Figure 12.33. Bridge scour depth versus time (Example 6).