Pier and Contraction Scour in Cohesive Soils (2004) / Chapter Skim
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Pages 93-110
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From page 93... ...
, therefore Z = 375 mm or 9.1% of Zmax 12.1.2 SRICOS-EFA Method: Computer Calculation Use SRICOS-EFA program Option 1: Complex Pier Scour Results: After a 2-year period of the flood having 3.36 m/s velocity, the final pier scour is Z = 4 m Table 12.1 and Figures 12.1 through 12.3 provide further information. Figure 12.4 illustrates the scour depth development with time.
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From page 94... ...
Of Layers 2 Thickness 10 Properties of 1st Layer Critical Shear Stress 2 Number of Regression Points Shear Stress vs. Scour Rate 8 Estimate Initial Scour Rate Value of Regression Points Shear Stress, Scour Rate 1, 0 2, 0.1 4,1 6,2 9, 3 20, 6 40, 8 60, 8.9 Thickness 20 Properties of 2nd Layer Critical Shear Stress 4 Number of Regression Points Shear Stress vs.
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From page 95... ...
. Channel geometry: Channel upstream width B1 = 50 m Flow parameters: Angle of attack: 20 degrees 70 years predicted hydrograph EFA result: Layer 1: Thickness 10 m; critical shear stress 2 N/m2 Layer 2: Thickness 20 m; critical shear stress 4 N/m2 Time duration: 70 years Determine: The magnitude of maximum pier scour depth 12.2.1 SRICOS-EFA Method: Computer Calculation Since the hydrograph is used in this case as hydrologic data input, the relationship between discharge and velocity and the relationship between discharge and water depth need to be defined.
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From page 96... ...
Of Layers 2 Thickness 10 Properties of 1st Layer Critical Shear Stress 2 Number of Regression Points Shear Stress vs. Scour Rate 8 Estimate Initial Scour Rate Value of Regression Points Shear Stress, Scour Rate 1, 0 2, 0.1 4,1 6,2 9, 3 20, 6 40, 8 60, 8.9 Thickness 20 Properties of 2nd Layer Critical Shear Stress 4 Number of Regression Points Shear Stress vs.
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From page 97... ...
. Approaching constant velocity V = 3.36 m/sec EFA result: Layer 1: Thickness 10 m; critical shear stress 2 N/m2
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From page 98... ...
Of Layers 2 Thickness 10 Properties of 1st Layer Critical Shear Stress 2 Number of Regression Points Shear Stress vs. Scour Rate 8 Estimate Initial Scour Rate Value of Regression Points Shear Stress, Scour Rate 1, 0 4, 1 6,2 9,3 6, 30 100, 10 200, 12.5 400, 16 Thickness 20 Properties of 2nd Layer Critical Shear Stress 4 Number of Regression Points Shear Stress vs.
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From page 99... ...
, therefore Z = 667 mm or 9.1% of Zmax 12.3.2 SRICOS-EFA Method: Computer Calculation Use SRICOS-EFA program Option 1: Complex Pier Scour Results: After a 2-year period of flood having 3.36 m/sec velocity, the final pier scour is Z = 7.1 m Table 12.3 provides a summary of input data. Figure 12.11 illustrates the scour depth development with time.
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From page 100... ...
Scour depth versus time (Example 3)
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From page 101... ...
of Layers 2 Thickness 15 Properties of 1st Layer Critical Shear Stress 2 Number of Regression Points Shear Stress vs. Scour Rate 8 Estimate Initial Scour Rate Value of Regression Points Shear Stress, Scour Rate 1, 0 4, 1 6,2 9,3 6, 30 100, 10 200, 12.5 400, 16 Thickness 20 Properties of 2nd Layer Critical Shear Stress 4 Number of Regression Points Shear Stress vs.
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From page 102... ...
Maximum hydraulic shear stress in contraction channel is (4) The initial rate of scour Z˙ is read on the EFA curve at τ = τmax Z˙ = 12.2 mm/hr (5)
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From page 103... ...
12.5 EXAMPLE 5: CONTRACTED CHANNEL WITH 60-DEGREE TRANSITION ANGLE AND APPROACHING HYDROGRAPH Given: Channel geometry: Upstream uncontracted channel width B1 = 150, contracted channel width due to bridge abutment B2 = 50 m, contraction length of channel L: = 30 m Abutment transition angle: 60 degrees Flow parameters: 70 years predicted hygrograph Manning Coefficient: 0.02 Hydraulic Radius: 2.72 m EFA result: Layer 1: Thickness 10 m; critical shear stress 2 N/m2 Layer 2: Thickness 20 m; critical shear stress 4 N/m2 103 B2 B1 Bridge Abutment Bridge Abutment 90° V1 River Bank River Bank Flow L 0 2000 4000 6000 8000 10000 12000 14000 0 200 400 600 800 Ti Maximum Contraction Scour Depth vs. Time (Example 4)
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From page 104... ...
Of Layers 2 Thickness 10 Properties of 1st Layer Critical Shear Stress 2 Number of Regression Points Shear Stress vs. Scour Rate 8 Estimate Initial Scour Rate Value of Regression Points Shear Stress, Scour Rate 1, 0 4, 1 6,2 9,3 6, 30 100, 10 200, 12.5 400, 16 Thickness 20 Properties of 2nd Layer Critical Shear Stress 4 Number of Regression Points Shear Stress vs.
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From page 105... ...
Shear stress (N/m2) 0 3 0.1 4 1 6 2 9 4 18.5 5 27 6 40 6.9 60 0 1 2 3 4 5 6 7 8 01 02 03 04 05 06 07 0 Sh EFA Result (Layer 2)
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From page 106... ...
W at er D ep th (m ) 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Maximum Contraction Scour Depth vs.
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From page 107... ...
Of Layers 2 Thickness 15 Properties of 1st Layer Critical Shear Stress 2 Number of Regression Points Shear Stress vs. Scour Rate 8 Estimate Initial Scour Rate Value of Regression Points Shear Stress, Scour Rate 1, 0 4, 1 6,2 9,3 6, 30 100, 10 200, 12.5 400, 16 Thickness 20 Properties of 2nd Layer Critical Shear Stress 4 Number of Regression Points Shear Stress vs.
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From page 108... ...
Shear stress (N/m2) 0 1 1 4 2 6 3 9 6 30 10 100 12.5 200 16 400 0 2 4 6 8 10 12 14 16 18 20 0 100 200 300 400 Sh EFA Result (Layer 1)
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From page 109... ...
109 Left Overbank Main Channel Right Overbank Approach Cross Section 0 100 200 300 500 600 700 800400 0 1 3 2 4 5 6 7 8 Distance, Meters El ev at io n, M et er s Figure 12.30. Cross-section view of approaching channel (Example 6)
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From page 110... ...
V el oc ity (m /s) 0 1000 2000 3000 4000 5000 6000 7000 0 10 20 30 40 50 60 70 Ti Scour Depth vs.
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