Riverbed deformation around multiple pile bridge piers under ice-covered conditions - experimental study in a large-scale flume and numerical simulation

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In Canada, ice cover can last up to six months in some regions. Under ice covered conditions, the location of maximum flow velocity is closer to the riverbed than during open flow conditions. Thus, riverbed scour depth around bridge piers under ice cover is greater than in the absence of ice cover. Excessive scour can cause damage to bridge pier foundations, such as occurred with the collapse of the Highway 16 bridge in Smithers, BC in 1966 and the bridge collapse in Port Bruce, ON in 2018. The proposed research will help us better understand local scour processes around multiple piers with different dimensions, shapes and arrangements under ice cover. This study will provide civil engineers with reliable results that can be used to modify bridge design guidelines that take the impact of ice cover into consideration.***This research will address some*important gaps in the scientific literature, including, (a) assessing local scour processes around multiple piers*under ice cover, (b) investigating*the impacts of the dimension/shape/arrangement of multiple piers on local scour*processes under ice cover, (c)*establishing equations describing the dependence of scour processes on flow*intensity, particle size, cover conditions, arrangement of multiple piers, and*compressed horse-shoe vortex under ice cover, and (d) developing a numerical model for simulating local scour*processes around multiple piers under ice cover.***Extensive*experiments will be carried out in a large scale flume which is 80-meters long,*2-meters wide and 1.3-meters deep. Five different non-uniform sands will be*used. Styrofoam sheets will be used as simulated ice cover (smooth, rough and*very rough). Analyses of the experimental data under both open-flow and ice-covered conditions will*focus on non-dimensional variables, such as shear Reynolds number, Shields*parameter and bridge pier*dimensions. Equations will be established to determine the scour depth under ice cover. ***Modeling the scour process will include modeling a strongly coupled system involving flow field, sediment transport and*bed morphology. The numerical model will consist of*three modules: a hydrodynamic module for the simulation of the flow field*around multiple piers, a sediment module for the modeling of suspended*sediment transport, and a bed variation module to account for the change in the*bed topography.***Numerical studies of the local scour*around multiple bridge piers will also be undertaken in the present research. One*of the priorities for the simulation of flow fields around multiple bridge*piers is to solve the vortex systems around the infrastructure. To solve the*vortex systems, either unsteady RANS (Reynolds-averaged NavierStokes equations) or Large Eddy Simulation will be used to*resolve the horseshoe vortex. The standard k-epsilon turbulence model will be*used first in the simulation for the flow field around multiple bridge piers*under ice cover. The RNG-based k-epsilon turbulence model will also be used in*the simulation.**