Abstract: Measuring the real contact characteristics between joint surface walls is challenging due to their inherent characteristics, which closely relate to the hydro-mechanical behaviors of rock mass. To quantitatively investigate the real contact area of rock joints under normal stress, rock engraving systems were used to manufacture a series of rough rock joints. The real contact area of rock joints was investigated using a multi-type pressure-sensitive film (MS, HS, and HHS), and an adaptive threshold method was utilized to recognize the scanning image of the film. Simultaneously, the contact stress transformed by the scanned film was also quantified. The evolution of the real contact area affects the mechanical characteristics of rock joints, characterized by the emergence, expansion, and coalescence of contact patches. The real contact area ratio increases hyperbolically with normal stress, and an empirical model can effectively predict the evolution characteristics. Joint roughness coefficient JRC has a positive correlation with initial growth rate of contact area. The contact points oscillate with increasing normal stress, and their growth rate has a negative correlation with the fractal dimension. Even at low normal stress (0.5 MPa), the highest contact stress can exceed 600 times the nominal normal stress. Distribution of the contact stress becomes more inhomogeneous with the increase of normal stress and roughness. The impact extent of roughness at high normal stress is approximately 20 times greater than at low normal stress. The experimental results can provide a reference for the constructive of the constitutive model and validation for numerical simulations

Key words: rock joints, contact area, closure deformation, pressure-sensitive film