Study on mechanical properties and mesoscopic damage mechanism of composite jointed rock masses

• Mechanical parameters of composite jointed rock masses exhibit pronounced anisotropy, with minimum elastic modulus and peak strength at a joint dip angle of 60°. • Increasing joint roughness reduces anisotropy and enhances energy storage capacity, with a strong linear relationship between elastic strain energy and peak deviatoric stress. • Joint dip angle controls the transition of dominant microcrack types from tensile to shear and back to tensile, as revealed by discrete element simulations. • Higher joint roughness suppresses damage localization along joints and increases the proportion of shear microcracks within the matrix by approximately 20%.