Pier and Contraction Scour in Cohesive Soils (2004) / Chapter Skim
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Pages 45-55
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From page 45... ...
The initial rate of scour for a given complex pier scour problem is obtained by first calculating the maximum shear stress τmax existing around the pier before the scour hole develops (flat river bottom) and then reading the initial scour rate on the erosion function obtained in the EFA test.
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From page 46... ...
The very favorable comparison gave confidence in the validity of the numerical results. 6.5 SHALLOW WATER EFFECT: NUMERICAL SIMULATION RESULTS The objective of this parametric study was to obtain the relationship between the maximum bed shear stress τmax and water depth (Figure 6.3)
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From page 47... ...
6.6 SHALLOW WATER EFFECT ON MAXIMUM SHEAR STRESS The maximum shear stress τmax is the maximum shear stress that exists on the riverbed just before the scour hole starts to develop. One way to present the data is to plot τmax/τmax(deep)
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From page 48... ...
Problem definition for water depth effect. By regression, the equation proposed for the correction factor kw giving the influence of the water depth on the maximum shear stress is k ew H B= ( )
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From page 49... ...
49 By regression, the equation proposed for the correction factor ksp giving the influence of the pier spacing on the maximum shear stress is 6.9 PIER SHAPE EFFECT: NUMERICAL SIMULATION RESULTS The objective of this parametric study was to obtain the relationship between the maximum bed shear stress τmax and the shape of rectangular piers (Figure 6.15)
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From page 50... ...
Initial bed shear stress distribution (N/m2) around the pier (H/B = 2, V = 0.3m/s)
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From page 51... ...
On the contrary, for L/B < 1, there is no region of separated flow and the decreasing pressure behind the pile may increase the velocity around the corner. 6.10 PIER SHAPE EFFECT ON MAXIMUM SHEAR STRESS The maximum shear stress τmax is the maximum shear stress that exists on the riverbed just before the scour hole starts to develop.
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From page 52... ...
) 52 6.11 ATTACK ANGLE EFFECT: NUMERICAL SIMULATION RESULTS The objective of this parametric study was to obtain the relationship between the maximum bed shear stress τmax and the angle of attack α defined as the angle between the flow direction and the pier direction (Figure 6.22)
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From page 53... ...
They also show that the location of the maximum shear stress moves backward along the side of the pier as the attack angle increases. 6.12 ATTACK ANGLE EFFECT ON MAXIMUM SHEAR STRESS The maximum shear stress τmax is the maximum shear stress that exists on the riverbed just before the scour hole starts to develop.
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From page 54... ...
) 0 1 1 5 90 6 5 0 57 54 6.13 MAXIMUM SHEAR STRESS EQUATION FOR COMPLEX PIER SCOUR In the previous sections, individual effects on the maximum shear stress are studied by numerical simulations.
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From page 55... ...
; • kw is the correction factor for the effect of water depth, defined as and the equation is kw = 1 + • ksp is the correction factor for the effect of pier spacing, defined as and the equation is ksp = 1 + • ksh is the correction factor for the effect of pier shape, defined as and the equation is ksh = 1.15 + • ksh = 1 for circular shape; and • ka is the correction factor for the effect of attack angle, 7 4 e L B − ; k circlesh = ( )
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