Abstract: The rock discontinuity morphology directly influences the macroscopic and microscopic characteristics of shear failure and shear strength. It is important to clearly recognize the stability of statistical parameters of morphology and anisotropy of nature rock discontinuities based on different interval point-cloud data. Thus, quantitative analysis is required to investigate the shear failure mechanism and to establish reasonable shear strength criterion. Three groups of natural rock discontinuity with different roughness characteristics were measured by using three-dimensional (3D) white light scanning system. The point cloud data of 15 different sampling intervals were further obtained according to the principle of sparse point cloud data density. Moreover, we studied the variation law of 2D statistical parameters (Z2、Rp、 ) and the corresponding 3D parameters (Z2s、Rs、 ) with the change of sampling intervals. The results show that these statistical parameters are decreased with the increase of the sampling interval, the attenuation amplitude increases gradually, and the quadratic polynomial function can be well characterized its relationship. Meanwhile, it is also found that the anisotropy of discontinuities at different sampling intervals also has interval effect. The constructed dimensionless parameter DAC (Discontinuity Anisotropic Coefficient) and the anisotropic characteristic parameters are used to quantitatively describe this phenomenon. The results indicate that the anisotropy of discontinuities has positive relationship with interval effect. Finally, comprehensive analysis is conducted on evaluating the stability of surface morphology parameters and anisotropic parameters of natural rock discontinues. These parameters are stable in the range of sampling intervals between 0.1mm and 0.5mm and their deviation is less than 3%. Therefore, the sampling interval is recommended to set to 0.5 mm when using 3D scanning to measure rock discontinuity.

Key words: rock discontinuities, point-cloud data, statistical parameter, interval effect, anisotropy