Reduction of Local Scour Around Cylindrical Bridge Piers Using Upstream Protective Piles-Article

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The study examines whether upstream protective piles can reduce local scour around cylindrical bridge piers. Scour forms when flow drives water downward at a pier, creating a scour hole and horseshoe vortex that remove riverbed sediment. Reducing scour can allow shallower, less costly foundations.<br /><br />Laboratory tests used a 9 cm-diameter cylindrical pier in a flume with cohesionless sand (median grain size 0.36 mm). Six small piles, arranged in a circle at 30-degree intervals upstream of the pier, were tested at radial distances of 8–24 cm. Scour depths were measured at three flow depths and compared with those around an unprotected pier.<br /><br />Pile spacing strongly affected performance. When piles were very close to the pier, the pile–pier assembly acted like a larger obstruction and produced deeper scour than the unprotected pier. The least scour occurred with piles 10 cm from the pier’s center, equivalent to a radial distance about 1.11 times the pier diameter. At this spacing, scour was reduced relative to the unprotected case. As spacing increased beyond this optimum, scour gradually increased toward a nearly constant value. Scour depth also increased nonlinearly with flow discharge.<br /><br />The authors conclude that upstream piles can be an effective scour countermeasure when appropriately positioned. However, results come from a limited set of laboratory tests using a specific pile arrangement and noncohesive sediment, so the findings should not be generalized to other site conditions without further investigation.

Keywords

scour reduction

bridge piers

upstream protective piles

local scour

horseshoe vortex

sediment erosion

flume experiment

pile spacing

cylindrical pier

riverbed scour