To assess the potential damage caused by a landslide to existing structures, an estimate of the impact forces is necessary. Several empirically based relationships have been proposed to calculate the peak force, but significant differences are obtained with various approaches. The earth pressure distribution along depth, which determines the bending moments on the structures, varies with time and flow characteristics. Simplified linear distributions (trapezoidal, triangular or rectangular) are commonly assumed, but the real distribution can be more complex. Advanced numerical analyses, capable of reproducing the key aspects of the phenomenon, can give a valuable insight into this problem. This paper investigates the potentialities of a numerical approach based on the Material Point Method (MPM) to the study of the interaction between flow landslides and retaining structures. The effect of different soil properties and boundary conditions on the impact force is discussed.