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51 9 8 7 H 6 5 kw B 4 3 2 1 0 0 0.5 1 1.5 2 2.5 H/B Figure 6.10. Relationship between kw (= max /max(deep)) and H/B. of L/ B = 4, the length of the flow separation is about 1 B from the corner; this may explain that max is independent of the B pier length for L/ B > 1. On the contrary, for L/ B < 1, there is S no region of separated flow and the decreasing pressure Flow behind the pile may increase the velocity around the corner. 6.10 PIER SHAPE EFFECT ON MAXIMUM Figure 6.11. Problem definition of pier spacing effect. SHEAR STRESS The maximum shear stress max is the maximum shear increased, however, when L/ B became less than one. Figures stress that exists on the riverbed just before the scour hole 6.16 and 6.17 indicate that the flow pattern around the rec- starts to develop. One way to present the data is to plot ksh = tangular pier for L/ B = 0.25 is quite different from the pattern max/max(circle) as a function of L/ B (Figure 6.21). The param- for L/ B = 4 where the flow is separating at the sharp corner. eter max(circle) is the value of max for the case of a circular pier For L/ B = 0.25 the flow is allowed to go behind the pier while in deep water and is given by Equation 6.1. The pier spacing the flow for L/ B = 4 follows the side of the pier. In the case correction factor ksh is the ratio max/max(circle). The data points 1 0.98 0.8 0.81 0.64 0.47 0.81 0.98 0.64 1.14 0.30 0.6 1.31 Y/B 1.48 1.82 = 0.47 0.4 0.2 0.30 Flow 0 -0.5 0 0.5 X/B Figure 6.12. Initial bed shear stress distribution (N/m2) around the pier (S/B = 1.88, H = 0.38m, V = 0.33m/s).