Computational Simulation of Live-Bed Bridge Scour Considering Suspended Sediment Loads

Abstract

While the suspended sediment loads play a very important role during the process of bridge-scour development, no computational models exist for reliable quantitative simulation and analysis of such loads during the scouring processes of live riverbeds. A three-dimensional simulation model for a live-bed bridge scour considering suspended sediment loads is proposed and validated in this paper. The major computational contribution of this new simulation model is the capability of simulating the dynamic equilibrium of inputs and outputs of sediments around bridge piers in a reliable and computationally efficient manner. First, aiming at the discrepancy between clear-water and live-bed scours, a two-phase flow model was applied where the water-sediment mixture flow was described via three conservation laws. The riverbed deformation induced by such water-sediment mixture flow was modeled based on a nonequilibrium sediment transport behavior. Specifically, (1) the developed representations and computational models enable the calculation of the substance exchange between the suspended sediment loads and bed loads in order to determine the geometric profile of the scoured riverbed; and (2) these models also capture the detailed transport behaviors and rates of suspended sediment loads and bed loads in order to support a quantitative derivation of the flux of such substance exchange. By doing so, the riverbed as a fluid model boundary can be updated in real time by tracing the calculated exchange flux; thus, the scour depth was dynamically simulated. Second, a simulation model of bridge scour was established with the consideration of suspended sediment loads. The advantages of adopting the proposed model were quantitatively and qualitatively validated by comparing to the experimental results on three aspects: (1) the suspended load distribution, (2) local scour depth, and (3) scour hole profile. Finally, case studies were conducted to parametrically investigate both the influence of the concentration of suspended sediment loads on the scouring and the validity of commonly used empirical formulas. The results assist engineers and researchers to better understand the impacts of suspended sediment loads on the bridge scour. The entire research indicates that the proposed live-bed bridge-scour modeling methodology enables simulation and analysis of the complex substance exchange and transport behaviors of suspended sediment loads during the live-bed scouring. Such a model could thus assure more accurate and reliable predictions and ought to be widely applied.