Liquefaction of saturated erodible bed sediments is often indicated as one of the main drivers for the bulking of geophysical mass flows and their extensive mobility, but this is especially difficult to capture in numerical models. In this work, we employ a two-phase 3D MPM–CFD model to simulate a granular column collapsing over a water-saturated erodible bed. The two-phase model explicitly simulates the solid and fluid phases and their interactions, thereby allowing the natural emergence of pore pressures, liquefaction, erosion, and flow runout within the simulations. Our results suggest that the initial dilatancy and permeability of the bed play crucial roles in governing the dynamics. Contractive beds with lower permeability exhibit larger pore pressure buildup and erosion, resulting in longer runout compared to dilative beds, consistent with field observations. These findings suggest the importance of considering the hydro-mechanical properties of erodible bed materials for predictive modelling of landslide hazards.