In southern Europe, debris flows pose a significant threat to infrastructure, particularly bridges, due to the high impact forces they can exert on piers. This study aims to analyse with MPM the impact of debris flows on bridge piers by considering three-dimensional effects and employing an advanced constitutive model capable of capturing regime transitions in the material. The primary objective is to investigate the impact force, distinguishing between peak and residual values, and to study the arching effect occurring between piers as their spacing varies. To achieve this, numerical simulations are conducted, comparing the results with a discrete element model (DEM) under completely dry conditions. The final goal of the research will the extension to saturated conditions to analyze the influence of water content on the stresses transmitted to the piers. The adopted approach will enhance the understanding of the interactions between debris flows and infrastructure, contributing to the design of more resilient and safer bridges in areas prone to such events.