Risk assessment from precipitation-induced landslides requires appropriate modeling of the interactions between soil and triggering meteorological phenomena. In the specific case of rapid shallow landslides similar to dense granular flows, you need a modeling approach for large rapid deformations in order to estimate the associated potential damage. The impact force exerted by the face of the earth flow on downstream structures should be estimated for damage assessment and for the design of effective protection interventions. In this article, a 3D FOSS (‘Free/Libre and Open-Source Software’) research code, based on the SPH numerical method (variant for weakly compressible fluids), is validated by simulating a shallow landslide on a 1:1 scale induced by rain, recorded in the Oltrepò Pavese. The code resolves vertical velocity gradients, thus providing a potentially more reliable representation of landslide dynamics and impact force. The mechanical parameters are consistent with the average soil characteristics, avoiding calibration procedures. The final landslide profile is compared with experimental observations for code validation, showing good consistency. The influence of geotechnical parameter uncertainties on the landslide front velocity and impact force on the valley wall are evaluated.