Q $3.$

For this bridge $5$ piers $($columns$)$ with spread footings are considered. the columns are

evenly spaced along this bridge. Design data are as follows:

$$ No of circular piers $=5$

$$ Diameter of each pier $=2\mathrm{.}5$ m

$$ Approximate height of middle pier $=11$ m

$$ Approximate height of other piers $=$ varies $($should be calculated$)$

$$ Height of spread foundation $=2$ m

$$ Spread foundation base dimensions $=5$m x $5$m

$$ Minimum depth of foundation from the riverbed to the base of footing $=4$ m

To control the local scour around pier foundations, gravel riprap is used. Close to the location of bridge, the river has a straight reach.

Q$3\mathrm{.}1.$ In order to control the local scour around pier foundations, coarse sand or gravel riprap is used. Close to the location of bridge, the river has a straight reach. Based on your previous calculations, check the depth of local scour for different mean diameter of gravel $(1$ mm$,2$mm$,5$ mm or $10$ mm$).$ Which one do you recommend? Explain why? $($Use the maximum flow of $3570\mathrm{.}226887)$