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

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 (d_st) around such piers has a very high priority nowadays. However, little work has been done in this regard. Most of the previous equations predict d_st 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 d_st 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.