Equation for time-dependent local scour at pier-like structures with eccentric in-line arrangements

Abstract

Excess scour developing around tandem and eccentric piers of side-by-side bridges may aggravate bridge failure. Thinking differently, this combination of pier-like structures may increase scour and shift sediments towards the bank, which may help in self-dredging. Therefore, accurate estimation of temporal scour depth (dst) around such piers has a very high priority nowadays. However, little work has been done in this regard. Most of the previous equations predict dst only for an isolated pier. Here, two to three piers are placed eccentrically in line in addition to isolated piers to derive equations empirically for accurate prediction of dst considering circular, triangular and square pier shapes. The present experimental results for an isolated circular pier are validated using equations from the literature, cross-validated with other published experimental data. Predictive equations are proposed for two to three piers with eccentrically in-line arrangements, taking their intermediate spacings as key variables. These equations are established based on dimensional analysis and non-linear regression. Overall analysis reveals that the estimated temporal scour depths based on the proposed integrated equation are closely within the ±80% accuracy band. The proposed equations can be used to predict temporal scour accurately for selected combinations of piers within the given experimental ranges.