Characterization Of 3-D Rock Discontinuities Roughness Based On Digital Image Processing Technique And Its Application

The presence of discontinuities is inherent to almost any rock mass and is a major contributor to strength and deformation of rock structures. Furthermore, the joint roughness is important to influence mechanics and hydraulics of the discontinuities. From the joint roughness coefficient proposed by Barton, researchers have worked hard to quantify roughness of discontinuities and proposed a lot of methods to describe joint surfaces. However, those methods still can not exactly character roughness of discontinuities owing to the surface topography is very complicated. Especially, there have no valid method to describe anisotropic characteristics and size effect of 3-D discontinuities roughness. In view of those problems, we develop the relationship between joint roughness and dimension D based on digital image processing (DIP) technique, propose a method to character anisotropy of 3-D rock surface roughness by variogram approach, discuss the relationship between the anisotropy and size effect of surfaces, and based on these researches, establish shear strength model considering anisotropic characteristics of discontinuities roughness. The works in the present paper can be summarized in the following:(1)Fractal description of rock joint based on digital image processing technique. First, we calculate the fractal dimensions (D) of the digitizing ten criterion profiles based on DIP method. On the basis of the asperity of a rough joint occurring on many scales, the fractal parameter is used to show the roughness character offered by secondary asperity, while the degree of waviness (A) is used to reflect the roughness property at the first order. In this respect, joint roughness coefficient (JRC) is represented using the fractal dimensions (D) and degree of the waviness (A), and their relationship is established. In addition, considering 3-D roughness characteristics of discontinuities, we propose an approach of estimating JRC with multi-fractal parameters based on multi-fractal theory. Firstly,3D data of discontinuities are obtained by DIP method. Secondly, the fractal dimension of surfaces is calculated by using the Projective Covering Method (PCM) and particularly the multi-fractal parameters of discontinuities are computed. At last, the relationship between the parameters of Aa(q) and ?(q) and the JRC is built according to the experimental data of shear strength. Thus, the JRC can be estimated accurately using multi-fractal parameters. The results provide a new approach for studying 3D discontinuities roughness.(2) Characterization of anisotropy of discontinuities roughness by variogram approach. The mechanical anisotropy of rock joint is greatly dependent on its surface roughness. To date it is still a key issue how to accurately quantify anisotropic characteristics of discontinuities. For this purpose, the variogram function was used to characterize anisotropy of joint surface roughness. First, a new index SRv related to both the sill and the range of variogram is proposed to describe the anisotropy of discontinuities roughness. Second, we develop the program using VC++ for calculating the parameters of variogram. Last, we analyze anisotropic characteristics of the gypsum sample surface. These results provide a new method for properly quantifying the directional variability of joint surface roughness.(3) Characterization of anisotropy of fracture aperture by variogram approach. First, according to physical implications of the variogram, a new aperture function (b) related to both the sill and the range of variogram is derived to quantify the fracture aperture. Second, a formula is developed for estimating aperture b of the discontinuities which's roughness trend accords with the two-stage spherical model and the b is calculated with a program written by ourselves. Last, the newly proposed aperture function b are calculated along 42 directions on the studied joint surface. These results provide a new method for properly estimating the mechanical and hydraulic properties of rock joints.(4) Characterization of Size effects of discontinuities roughness based on anisotropic properties. The aforementioned index SRv is used to analyze size effects properties of rock discontinuities. To investigate the size effects of surface roughness of rock joints, ten sampling windows ranging of size from 100 Pixel×100 Pixel to 1000 Pixel×1000 Pixel were selected from five different part of the surface and their SRv values were calculated. The results show that the size effects of discontinuities roughness interacts with the anisotropic properties. The study results can provide guidance for quantitative analysis of the right direction of mechanical property of joint surface and offer a new method to choose an appropriate sample size in the laboratory or field tests.(5) A shear strength model accounting anisotropy in rock joints behavior. By considering asperity inclination angle and amplitude, a new parameter ? used to describe discontinuities roughness was proposed, which was expressed by both the anisotropy index SRv and amplitude index A. Then, the relationship between the JRC and the ?, was built from calculating the ten standard roughness profiles. Last, a shear strength model considering anisotropy was developed based on Barton's peak shear strength criterion and was validated by shear tests. In this context, this paper aims to provide an effective means of estimating the mechanical properties of rock joints in all directions.