Effect of Sampling Interval and Anisotropy on Laser Scanning Accuracy in Rock Material Surface Roughness Measurements

Three-dimensional laser scanning is an advanced technique for fracture roughness measurements. The surface roughness of fractures (discontinuities) accurately measured is of practical importance for proper evaluation of the mechanical properties of a fractured rock material. It is also appropriate to perform a more systematic study on the effect of a sampling interval on the roughness measurement accuracy. This effect was investigated based on the 3D-point-cloud data of a fracture surface acquired with laser scanning. A series of 2D profiles corresponding to twelve directions were extracted from concentric circular sampling windows of different diameters. The roughness measurement accuracy is quantified by the three parameters, viz the mean square first derivative Z₂ , structure function SF, and roughness profile index R_p . The sampling interval effect was investigated for its different values by analyzing the three parameters of different profiles. It was established that SF was very sensitive, while Z₂ and R_p were less responsive to the sampling interval. It exerts a much weaker influence on the rock material fracture roughness in comparison with anisotropy.