Developing new equations for maximum scour depth near tandem, side-by-side, and eccentric piers

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There is a significant gap in the study of interference effects on side-by-side, tandem, and eccentric piers, which is critical for bridge design. This study investigates how hydraulic parameters affect the maximum scour depth (dm). These are pier spacings, flow intensity, flow shallowness, flow skew angle, sediment coarseness, sediment gradation, and time. Three different sets of equations are proposed to determine the dm around side-by-side, tandem and eccentric piers, considering multiple factors and comparing them with existing literature. The accuracy of the equations is evaluated using statistical parameters such as correlation coefficient (R), Nash-Sutcliffe efficiency (NSE), normalized root-mean-square-error (NRMSE) and index agreement (IA). The tandem front pier equation shows the highest accuracy with R=0.91, NSE=0.83, NRMSE=0.23, and IA=0.95. Likewise, the tandem rear pier equation excels in the highest accuracy with R=0.83, NSE=0.69, NRMSE=0.31, and IA=0.90. This research improves the robustness of scour prediction equations for two-piers by studying influential parameters.