Abstract: The morphological features and mechanical properties of rock structural surfaces are important scientific issues in the field of rock mechanics and engineering geology at home and abroad. The borehole images can accurately record the hole-wall information of borehole and the morphological feature of in-situ rock structural surfaces in the borehole. In this paper, a method for analyzing and extracting the outline of rock structural surfaces based on borehole images is proposed, which is used to study the three-dimensional morphological features and mechanical properties of rock structural surfaces. In view of the uniqueness of the contour line of the rock structural surfaces in the image, the three-dimensional morphological features of borehole rock structural surface are accurately restored by the following steps: information extraction, coordinate transformation, ring information analysis and contour line’s sampling processing. Then, the roughness and anisotropy of rock structural surfaces are described by fractal dimension of each section of the contour. Finally, the dominant sliding direction of rock structural surfaces can be determined according to the fractal dimension and then the shearing strength of the structural surface can be evaluated for further explanations. Results show that the transformed contour line of the structural surfaces based on borehole images can well reflect the three-dimensional morphological features of rock structural plane in the borehole, which can be used to determine the dominant anti-slip direction and to estimate the shear strength of rock structure plane in practical engineering application.

Key words: borehole image, rock structural surface, fractal dimension, dominant anti-slip direction, shear strength