This paper presents a numerical model based on Discrete Element Method used to reproduce a series of tests of dry granular flow impacting a rigid wall. The flow was composed of poly-dispersed non-spherical particles flowing in an inclined chute with different inclination angles. The model has been calibrated based on the flow thickness measurements and the shape of the flowing particles (a single sphere and a clump). Quantitative comparison with experimental data showed good agreement in terms of peak impact force on the wall, the time of the peak and also the residual force values at the end of the tests. After validating the model, relation between microstructure and the normal impact force against the wall was investigated, by comparing the variation of impact force values along the height of the wall for different tests. Microstructural heterogeneities were observed in the impacting and depositing stages of the flow, indicating the presence of arching effect in the granular medium behind the wall.