Local scour at a complex pier with inclined columns footed on capped piles: effect of the pile arrangement and of the cap thickness and elevation

Experiments were performed for local scour at a complex pier with two inclined, rectangular columns footed on a group of circular piles with a pile cap. The research fills a gap in existing literature, where studies for complex piers have considered a single, vertical column. The laboratory campaign involved the variation of the pile diameter and arrangement, and of the cap thickness and elevation above the non-scoured bed. The results of carefully conducted scour runs revealed the cap elevation as a most influential parameter. In cases of buried and partially buried pile cap, in fact, the cap acted as a scour countermeasure. For high cap elevation, the supporting piles were also exposed to the flow and their size influenced the resulting scour depth values as it directly impacted on the pier frontal area. The measured scour depth was compared to the values predicted by several literature methods for complex piers with a vertical column, supporting the possibility to extend their use to the geometry investigated in the present study.