Effect of seepage flows on the performance of foundations of bridges within watercourses

The foundation soil of bridge piers located within watercourses is subject to variations in pore water pressure due to seepage flows through the surrounding soil. This study investigates pore pressure variations in the foundation soil induced by seepage flows associated with water level fluctuations around bridge piers and evaluates their influence on effective stresses and foundation performance. Three case studies of Italian bridges crossing the Malone, Vara, and Aso rivers are analyzed. Hydraulic simulations of the piers were performed using Ansys Fluent to extract pressure values along the riverbed, which were subsequently applied as boundary conditions in FLAC3D software to assess the distribution of pore water pressures around the foundation. The main contribution of this study lies in a numerical approach that enables the transfer of pressure fields at the riverbed to a three-dimensional porous medium model, allowing an explicit evaluation of the variations in pore pressures induced by seepage flows and their influence on foundation behavior under scour conditions. The results indicate that pressure variations in the soil, induced by fluctuations in the water level around the pier, have a marginal impact on the stress state of the soil in geotechnical terms, and consequently on the bearing capacity of the foundation. However, the pore pressure values observed in the uppermost soil layers may provide useful insights into how seepage can influence the stability of excavation near the foundation.