This paper discusses a new computational strategy for the analysis of inelastic processes in granular rocks subjected to varying levels of confinement. The purpose is to provide a flexible and efficient tool for the analysis of failure processes in geomechanical settings. The proposed model is formulated in the framework of Lattice Discrete Particle Models (LDPM), which is here calibrated to capture the behavior of a high-porosity rock widely tested in the literature: Bleurswiller sandstone. The procedure required to generate a realistic granular microstructure is described. Then, the micromechanical parameters controlling the fracture response at low confinements, as well as the plastic behavior at high pressures have been calibrated. It is shown that the LDPM model allows one to explore the effect of fine-scale heterogeneity on the inelastic response of rock cores, achieving a satisfactory quantitative performance across a wide range of stress conditions. The results suggest that LDPM analyses represent a versatile tool for the characterization and simulation of the mechanical response of granular rocks, which can assist the interpretation of complex deformation/failure patterns, as well as the development of continuum models capturing the effect of micro-scale heterogeneity.