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<br />Since the west river bank has a slope of 1H:1V, an average value is used for the length <br />of abutment that projects perpendicular to the flow. The abutment extends 2.4 m at the <br />water surface and 0 m at the channel bed (see Figure 6.4). Therefore an average value <br />of: <br />b. = (2.4 + 0)/2 = 1.2 m. <br />This is less than the minimum, therefore b. = 1,5 m. <br /> <br />3. From Figure 6.2 or the design equation calculate the equivalent spherical diameter, 0", <br />for Vv = 2.87 mls and b. = 1.5 m. <br /> <br />(1.4)Du = 0.255(2.87}J1.5/9.806 ::) Du = 0.204 m = 204 mm <br /> <br />For the west abutment, the 100 kg Toskane is selected (Ou = 430 mm). A smaller 50 kg <br />Toskane could have been selected, but this non-standard size may not be economical to <br />manufacture. <br /> <br />4. Since the engineer is confident about the flow velocity and the channel is assumed <br />vertically stable, a pad radius of f. = 2.0b. is recommended. <br /> <br />Pad Radius, f. = 2.0(1.5) = 3,0 m. <br /> <br />The Toskanes will be installed along the abutment and wingwalls a horizontal distance of <br />3 m from the wall. An additional 600 mm of pad will be added at the ends of the pad for <br />freeboard. <br /> <br />5. The pad thickness is 20u which will result in <br />7.08 Toskanes/m2. The total area of the <br />pad (see Figure 6,6) is: <br /> <br />Area of Pad <br /> <br />Area = (3)(9) + 2(3)(5) + 2(0.5)(3)(1.8) + <br />2(0.5)(3)(4) = 74.4 m2. <br /> <br />#Toskanes = (74.4)(7.08) = 527 Toskanes. <br /> <br />6. A filter is placed under the pad for the bed <br />material of cobbles and gravel. The d85 of a <br />granular filter is 95 mm. <br /> <br />0m <br /> <br /> <br /> <br /> <br />-l 3.. 1-' <br /> <br /> <br />,. 1]- <br />~ <br />~ <br /> <br />The disadvantage to selecting an oversized <br />unit is that larger units have larger voids which <br />increase the opportunity for pumping of the bed <br />material if a filter is not present. A well <br />designed filter should be property installed <br />under the pad. More excavation is also <br />required for the oversized Toskanes, but fewer <br />Toskanes need to be manufactured for this <br />design. <br /> <br />FIgure 6,5 Area of Abutment Pad <br /> <br />6.11 <br />