ABSTRACT
Joints which are widely distributed in rock masses concern engineers when conducting underground constructions, such as the underground oil depots and power stations. It is well known that the roughness of discontinuities which are clean and unfilled will have great impacts on both hydraulic and strength characteristics of discontinuous rock masses (Tatone & Grasselli, 2010; Jang et al., 2006). Therefore, extensive investigations have been conducted on the mechanical properties of joints and the morphology characteristics of joint surfaces. Firstly, the accurate measurement of joint surfaces is prerequisite to investigate
morphological parameters and to set up corresponding models. To data, non-contact and contact techniques are often used to gauge joint surfaces. The non-contact laser morphology instruments are widely used due to the high accuracy. Secondly, to investigate the morphologies of the joints obtained, the statistical and
fractal geometry theories are mostly applied. Initially, research interests were focused on 2D parameters of the joint surfaces. However, the 2D parameter descriptions are limited by the descriptions of the surface in 3 dimensions which are more realistic. Therefore, 3D parameters were developed. Xia (1996) quantified the height characterization parameters of joint surface topography with the mathematical method and identified the waviness and unevenness components for joint surface profiles. Zhao (1997a,b) pointed out that the mechanical properties of a joint, which are related to the coupling degree of two joint surfaces, were poor when the coupling degree was limited, and the joint coupling parameter which varies from 0 to 1 was put forward to describe the degree of coupling between the two halves. The JRC-JMC shear strength criterion was also brought up, based on the Barton JRC-JCS model (Barton & Choubey, 1977). To investigate the morphological evolution of joint surfaces under cyclic shear loads, Homand et al. (2001) developed several parameters, including θs, Ka and Rs, to quantify morphological characterization of joint surfaces, and proposed morphmechanical model of direct shear tests. Grasselli and others (Grasselli, 2006; Grasselli & Egger, 2003; Grasselli et al., 2002) proposed the 3D shear model based on 3D parameters of joint surfaces. Other researches on morphological parameters of rock joint surface have also been done in recent years (Lee et al., 2001; Jiang et al., 2006; Cao et al., 2011; Chen et al., 2010; Belem et al., 2000). Barton & Choubey
(1977) proposed ten typical roughness profiles and the corresponding JRC values, and then one shear criterion containing JRC was further proposed. However, the estimation of JRC requires a great deal of experiences. Hence, lots of methods were proposed to estimate JRC values (Tse & Cruden, 1979; Andrade & Saraiva, 2008; Beer et al., 2002; Du et al., 2009; Yang et al., 2001). Tatone & Grasselli (2010) tried to establish empirical relationship between the new 2D roughness parameters and JRC which enabled shear strength estimation according to the Barton-Bandis shear strength criterion. Fractal geometry set up by Mandelbrot (1983) is a useful method to investigate irregularity in the nature. Irregular profiles of joint surfaces have self-similarity in statistics. Carr & Warriner (1989) introduced fractal theory to study morphology of joint surfaces firstly. The Fractal dimension and amplitude were used as parameters to describe morphology characteristics of joint surfaces. At first, the fractal dimension of profile was computed, later, that of joint surface was computed by different methods (Odling, 1994; Kulatilake et al., 1995). Xie et al. (1997) computed fractal dimension of profiles which was between 1 and 2, and that of joint surface was between 2 and 3. Thirdly, coexistence of joints and water is frequently encountered in rock engineer-
ing. Colback&Wild (1965) found that the influence of water-rock interaction on rock mass strength is prominent. According to the experiment of Rebinder et al. (1994), at the prophase of the water-rock circle interaction, rock was under a more serious damage effects both physically and chemically, in which the cohesive strength and internal friction angle were influenced most. The physical and chemical damage effects on rock were reduced as the actuation duration was prolonged and times were added (Melo et al., 2008, 2007). Indratna et al. (1999) indicated that the influence on cohesive strength and internal friction angle was reduced as well and the changes became gentle. So, it can be inferred that the properties of the discontinuities, as special rock masses, will also be affected by the water-rock interaction, and rock strengths even engineering stabilities might be influenced by the water-rock interaction in further. Therefore, there is an urgent need to determine more accurately the relationship between rock and water-rock interaction (Zhao et al., 2006; Sari & Karpuz, 2006; Jiang et al., 2004; Pyrak-Nolte &Morris, 2000; Hoek & Diederichs, 2006). The surface properties with water-rock interaction have amajor influence on the hydro-mechanical behavior of the rock masses and rock joints. Many parameters (Zhang et al., 2002; Jae-Joon, 2006; Zimmerman et al., 2004), for instance hydraulic conductivity, frictional resistance and resistance to shearing along discontinuities, will change with the effect of water-rock interaction. There are strong links between roughness and these parameters. Although previous studies have provided important information regarding accurate characterization of rock surface roughness, most studies concentrate on characterizing surface roughness of rock using small samples and no systematic study has been made to investigate the effect of water-rock interaction using large 3D rock samples. To investigate the morphology characteristics of coupled joints, typical parameters
used to characterize joint morphologies are introduced firstly. And a feasible method to generate the coupled joints has been proposed too, analysis based on above parameters has been conducted to investigate the characteristics of these coupled joints. And then, further investigation on the influence of water content on the joint morphologies obtained by conducting Brazil tensile tests has been conducted. Finally, the effects of water-rock interaction on rock and morphologies of the coupled joints by shear tests have been investigated.
