Our study presents a framework using the open-source DEM tool LIGGGHTS[1] to conduct triaxial compression simulations of pebble beds[2] to extract Drucker-Prager (DP) model parameters for varying particle size distribution (PSD). In this study, we have analyzed six numerical samples comprising PSD with a mean radius of 0.5 mm with the Gaussian distribution of pebble radii ranging from 0.1 mm to 0.9 mm, as shown in Figure 1. This work focusess on investigating the granular behavior of pebble beds by analyzing the model DP model parameters extracted from a poly disperse RVE (Representative Volume Element). The primary objective is to understand the effect of PSD on the granular response of the system. One of the important DP parameter is the mesoscale friction angle, estimated by plotting the point of failure in the meridional plane. Friction angle is a measure of granular strength and defined as the angle between the failure surface and the hydrostatic axis in the pressure- deviatoric stress (p-q) plane. Another important parameter is the dilatancy angle, extracted from the triaxial compression simulation data and related to the dilatant behavior of the initial hydrostatic compressed sample. The simulation is conducted for different confinement pressure ranging from 0.1 MPa to 0.8 MPa. The resulting simulation data provides rich insight into the microscopic particle level interactions and their relation to the macroscopic response of the pebble assembly.