The understanding and quantification of mudflow and debris flow – structure interactions in terms of modification of the incident flow and impact force applied to the obstacle are of paramount importance for the conception and design of structural countermeasures. In this context, the present study aims at determining local values of the flow velocity and pressure in the vicinity of a structure subjected to a debris-flow impact, as well as the changes in these variables over time and space, for a given incident flow. We use a 2D vertical numerical model based upon the SPH (smoothed particles hydrodynamics) numerical method. SPH is a particular method of treatment of fluid mechanics equations which is suitable for computing highly transitory free surface flows of complex fluids in complex geometries. Thus, it is suitable for the treatment of debris-flow waves – structure interactions. We present our numerical experiments setup aiming at simulating a viscoplastic fluid wave impacting a simple obstacle. We notably focus interest on the pressures developed on the structure during the impact, on their evolution with the incident flow features, and on their spatial distribution over the obstacle. We also analyze our results in terms of dynamic and gravity pressures.