A model of bridge pier scour during flood waves

Abstract

The time-dependent bridge pier scour during flood waves is analysed. Scour experiments were conducted in a novel installation able to produce complex hydrographs with high precision. Experimental data were used to test scour formulas including a new mathematical model. Results confirm the reliability and superior performance of the proposed dimensionless, effective flow work based model under steady and unsteady hydraulic conditions. Analyses highlight the impact of different hydrographs on scour, demonstrating the strong control by the hydrograph shape of the temporal evolution of scour depth and scour rate, although final scour after a flood only depends on the total effective flow work exerted by the hydrograph on the sediment bed. Hysteresis between flow discharge and scour rate is reported and explained. Flow acceleration is shown to play a minor role in scouring. The proposed model is a promising alternative for computation of local scour under highly unsteady hydraulic conditions

BRISENT: An Entropy-Based Model for Bridge-Pier Scour Estimation under Complex Hydraulic Scenarios

“…Z * = z/z R is defined as a normalized parameter, where z is the dimensional scour depth and z R the reference length established previously. In agreement with Link et al [22], Z * increases monotonously over W * , taking values from zero at non-eroded conditions to a maximum value at the equilibrium state. Based on the Laplace principle of insufficient reason and therefore, assuming that all values of W * between zero and a maximum considered value, W * max are equally likely to be attached (not necessarily true), then the probability of the relative scour depth to be equal to or less than Z * , Pr(Z * ≤ Z * ) = F(Z * ), can be specified by W * /W * max .…”

“…The BRISENT model was validated using highly unsteady and multi-peaked hydrographs pertaining to Link et al [22]. Validation runs are plotted on Figure 7a-d, presenting the timedependent evolution of the measured scour depth in contrast to the BRISENT model calibrated and estimated according to the proposed equations (Equations (22), (26) and (27)). )…”

“…Experimental data were compiled from available studies in Chabert and Engeldinger [58], Zanke [10], Franzetti et al [59], Oliveto and Hager [14,19], Sheppard et al [60], Grimaldi [61], Alabi [62], Simarro et al [63], Meyering [64], Lança et al [65], Link et al [22] and Pizarro et al [21]. Altogether, results corresponding to 137 experiments were analyzed.…”

“…The experiments are presented in Table 1. Based on the unique relationship between W * and Z * (under clear-water conditions, constant sediment properties, and geometrical scales) [21], unsteady experiments were calibrated in two ways: [21] and Link et al [22]. This kind of calibration will be called "steady calibration" in the rest of the paper.…”

“…For validation procedures, the most complex experiments were used among those available to the authors: two highly unsteady and multi-peaked runs pertained to Link et al [22] (2017LINK01U and 2017LINK02U).…”