PSI - Issue 84

Luca Vené et al. / Procedia Structural Integrity 84 (2026) 529–535

535

5. Conclusions The study examined seepage flow within the foundation soil of the riverbed, characterized by coarse-grained deposits. Local scour geometry was idealized based on conceptual models available in literature. The numerical results show that seepage in the vicinity of the foundations modifies the pore water pressure field, leading to localized variations in effective stress and, consequently, in the soil shear strength. Regarding the pressures beneath the pile cap, values slightly lower than the hydrostatic pressure are observed in the upstream half of the plinth, followed by slightly higher values in the downstream half. Along the vertical sections located around the foundation base, mildly positive pressure differences are identified along the lateral and downstream sections. However, these variations generally remain within a range of a few kilopascals and do not result in a significant modification of the soil shear strength. For the pressure trends along the foundation piles, it was observed that when the pile head remains below the riverbed surface, the presence of seepage flow induces a reduction in pore water pressure relative to the hydrostatic condition. This reduction leads to an increase in effective stresses and shear strength, although the resulting variations remain generally limited and do not pose concerns in terms of geotechnical safety. A different scenario arises when, due to erosion, the riverbed level is lowered below the base of the foundation footing. Under these conditions, the pressure distributions show positive ΔP values in the case of generalized lowering, whereas in the localized scour scenario slightly positive pressures are recorded in the first few centimeters of soil, gradually becoming negative with increasing depth. In both erosion configurations, these variations have limited impact on the stability of the foundation; however, they may become relevant when assessing the stability of the excavation around the foundation. In particular, in the case of a generalized lowering of the riverbed by 3 m and 4.5 m, pore pressure values were observed that reduce the effective stresses to zero over a depth of approximately 30 cm, leading to a null shear strength and potentially facilitating soil removal by the river flow. Acknowledgements The authors wish to thank Satap S.p.A. (Turin, Italy), part of the ASTM Group, for providing the data used in this study and for supporting the industrial PhD program. References API, 2011. Geotechnical and foundation design considerations, API RP 2GEO. American Petroleum Institute, Washington, D.C., USA. Bennett, C.R., Lin, C., Parsons, R.L., Han, J., 2009. Evaluation of behavior of a laterally loaded bridge pile group under scour conditions. Structures Congress 2009, Austin, TX, USA. Brown, D.A., Castelli, R.J., 2010. Drilled shafts: construction procedures and LRFD design methods, FHWA NHI-0-016. Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., USA. Chen, Y.F., Ai, Z.Y., Ma, Z.G., Ye, Z.K., 2022. Influence of scour on the vertical response of rock-socketed piles in layered saturated rock–soil mass. International Journal for Numerical and Analytical Methods in Geomechanics 46, 3074–3095. Diab, R., Link, O., Zanke, U., 2010. Geometry of developing and equilibrium scour holes at bridge piers in gravel. Canadian Journal of Civil Engineering 37(4), 544–552. Hannigan, P.J., Gobe, G.G., Likins, G.E., Rausche, F., 2006. Design and construction of driven pile foundation, vol. I. FHWA-NHI-05-042. Federal Highway Administration, U.S. Department of Transportation, Washington, DC, USA. Lin, C., Jiang, W., 2019. Evaluation of vertical effective stress and pile tension capacity in sands considering scour-hole dimensions. Computers and Geotechnics 105, 94–98. Lin, C., Wu, R., 2018. Evaluation of vertical effective stress and pile lateral capacities considering scour-hole dimensions. Canadian Geotechnical Journal 56, 135–143. Lin, Y., Lin, C., 2019. Effects of scour-hole dimensions on lateral behavior of piles in sands. Computers and Geotechnics 111, 30–41. Wang, Z., Zhou, H., Sheil, B., Liu, H., Wang, C., 2023. Numerical investigation of the lateral response of pile groups in sand under local scour conditions. Computers and Geotechnics 159. Yang, Y., Qi, M., Wang, X., Li, J., 2020. Experimental study of scour around pile groups in steady flows. Ocean Engineering 209.