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.