Effect of seepage flows on the effective stress state around bridge pier foundations: a case study

The foundation soil of bridge piers located within watercourses may experience variations in pore water pressure due to seepage flows triggered by fluctuations in the water level and velocity around the piers. This study specifically investigates the impact of such phenomena on the effective stress state and, consequently, on the performance of the foundation of the highway bridge crossing the Malone stream (Turin, Italy). Three-dimensional computational fluid dynamics (CFD) simulations were conducted using Ansys Fluent to determine the distribution of water pressure on the riverbed in the vicinity of the pier. The resulting pressure values were then applied as boundary conditions in a FLAC3D model to assess the distribution of pore water pressures within the foundation soil. The results indicate that the pore pressure distributions induced by the interaction between the current and the pier have a marginal effect on the stress state of the soil and on the bearing capacity of the foundation. However, under specific conditions, the pore pressure values recorded in the shallowest soil layers suggest that seepage flows may play a non-negligible role in the evolution of local scour near the pier.