Abstract: To better describe the coincidence degree of rock, the point cloud alignment algorithm was employed to calculate 3D joint matching coefficient (JMC3D) in this study. Firstly, 3D laser scanning technology was used to collect point clouds of rock discontinuities, including upper and lower joints. Then point clouds from both reference surface and testing surface of rock discontinuities were registered into the same global coordinate system, based on the iterative closest points (ICP) algorithm. Moreover, the corresponding Z-coordinate difference between the aligned testing surface and the reference surface was calculated. These point clouds, with Z differences in the range of alignment errors, were regarded as the matching portions. Finally, the percentage of matching portions was calculated to represent the parameter of JMC3D. The comparison of shear strength results obtained from direct shear tests in the laboratory and JRC-JMC model was conducted to clarify the reliability of the proposed method. The relative errors of four joint specimens were 7.38%, 3.21%, 9.03%, and 10.02% respectively, which indicated that the presented calculation of JMC3D was characterized by high feasibility and good performance. Meanwhile, this study revealed that there was a close relationship between the parameter of JMC3D and shear strength of rock discontinuities.

Key words: rock discontinuities, point cloud data alignment technology, 3D joint matching coefficient, shear strength