Abstract: The initial contact of the two surfaces of a joint has important effect on its shear and coupled shear-flow properties. TJXW-3D portable rock surface topography scanner developed by Tongji University is able to realize special reference points. In this article, the scanner was first used to digitize joints in initial closed state and joint with two surfaces, respectively. With permanent reference points attached to the sides of the joint samples, the subsequent measurements were automatically transferred into the coordinate system of the first measurement, thus the void space of the joint in initial contact can be obtained. The aperture distributions of void spaces of three joints with different surface roughness under initial contact state were analyzed, and the results were in accordance with prior studies. The aperture of joints ranged from 0.31 mm to 0.41 mm, following Gaussian distribution. Furthermore, the Brown joint closure model was used to demonstrate the application of the void space calculation method, and the result was compared with that of normal compression test. The Brown model result was larger than test result as Brown model does not consider the interaction between upheaves. The result lays a foundation for the numerical research on the coupled shear-flow property of joint.

Key words: joint, void space, initial contact state, aperture distribution, Brown model