This Thesis addresses the issue of rockfall instability and its mitigation, focusing specifically on the case study of a slope in Varallo (VC, North-West Italy). This region has been prone to rockfall phenomena over the years, with significant consequences for the road situated at its base. Through the application of Rocfall 3D using the Rock Science Simulation Tool, the study evaluates the rockfall risk and proposes strategies to enhance the safety of the infrastructure. The analysis begins by estimating the rock block volume for the simulations, referred to as the design block, using various methodologies available in the literature. These include simpler methods based on blocks already fallen at the slope’s base, as well as more complex statistical analysis.