Complex piers (CPs), consisting of a column, pile cap and pile group, are commonly built as foundations for hydraulic and marine structures. Scour-hole development around CPs is studied in this paper. A total of 52 tests is carried out on 4 CP models, with experiments durations ranging from 24 to 120 h. All of the available experimental data for clear-water scour around CPs including the collected data of the present study and those previously published are reviewed and combined into a database. A special case of bridge piers with deep foundation or caisson instead of pile caps is also considered, which is herein called compound piers. The database contains 367 experiments for CPs and 162 experiments for compound piers. The predictive equations of the maximum scour-hole depth at complex piers including HEC-18 and FDOT equations are revisited and a new equation is proposed. Comparisons of the prediction equations shows that for CP data, the absolute error is 28%, 79% and 108% for the proposed, HEC-18 and FDOT equations, respectively. Underestimation below
20% error line occurs for 11%, 15%, and 7% of the cases in the proposed, HEC-18, and FDOT equations, respectively. For compound piers, the proposed equation has 41% absolute error while HEC-18 equation has 93% absolute error.

Keywords