Numerical study of local scour and hydrodynamic pressure of complex bridge piers

• This study uses a new rheological model, the Discontinuous Bi-Viscous Model (DBM), to simulate the rheology of the mud riverbed. • A newly non-Newtonian fluid model, DBM introduces a discontinuous rheology relationship between the un-yield and yield region. • The new rheological model can predict the local scour around complex bridge piers. • The hydrodynamic pressures on each exposed pile are computed and compared with that in the bridge design code. This study uses Computational Fluid Dynamics to investigate bridge foundations' scouring process and hydrodynamic pressure caused by an extreme flood. A Large Eddy Simulation model, compiled with a Navier-Stokes equations model, is used to compute the fluid motion with the Volume-of-Fluid to track the motion of the water surface. A Discontinuous Bi-viscosity rheological model describes the river's muddy bottom properties. The numerical results are further analyzed to understand the influence of exposed, closely spaced piles bridge on the scouring process. The results show that the extended foundation (with ten piles) has a maximum scour depth of approximately 10 m, which is 2.0 m greater than the non-extended foundation (with six piles). Specifically, the high velocity surrounding the exposed, tightly spaced piles may exacerbate the scouring problem. The design code suggests a hydrodynamic pressure of 10.9 kPa and 10.1 kPa for six and ten piles, respectively. The front-row piles' hydrodynamic loading is underestimated in the bridge design code. The maximum hydrodynamic pressure occurs at the front piles at roughly 1.8P I , where P I represents the hydrodynamic pressure. The velocity and hydrodynamic pressure at each pile are calculated, comparable with that in the bridge design code. This finding is important for the design of bridge foundations with exposed piles.