<p>The deformation properties of fractured rock mass are fundamental in engineering design considerations, influencing the stability and performance of structures such as dams, tunnels, and foundations. Accurately determining this parameter is challenging due to the presence of various fractures within the rock mass. Traditional methods, both direct and indirect, have limitations in accounting for the complex geometry and mechanical interactions of these discontinuities. In this study, a numerical framework is presented to evaluate the rock mass deformation modulus using a combined Discrete Fracture Network (DFN) and Distinct Element Method (DEM) framework based on plate loading tests. The modeling is performed using 3DEC, where fracture networks generated from geological surveys are embedded within an intact rock matrix. The model is validated using both continuous and discontinuous rock blocks based on data from the Bazoft and Bakhtiari Dam projects. The Azad pumped-storage power plant site is employed as the primary case study to conduct joint stiffness sensitivity analyses and to investigate scale effects and determine the Representative Elementary Volume (REV). Sensitivity analyses demonstrate the significant influence of joint normal and shear stiffness on the deformation modulus. In addition, the effect of model dimensions on the deformation modulus is also investigated to identify a Representative Elementary Volume (REV), beyond which the deformation modulus becomes stable. These results indicate that the proposed numerical framework provides a practical and reliable numerical approach for simulating plate loading tests and estimating the deformation modulus of fractured rock masses.</p>