Abstract
Measurement and estimation of the joint roughness coefficient (JRC) is a critical but also difficult challenge in the field of rock mechanics. Parameters for estimating JRC based on a profile derived from a fracture surface are generally two-dimensional (2D), where a single or multiple straight profiles derived from a surface cannot reflect the roughness of the entire surface. It is therefore necessary to derive the three-dimensional (3D) roughness parameters from the entire surface. In this article, a detailed review is made on 3D roughness parameters along with classification and discussion of their usability and limitations. Methods using Triangulated Irregular Network (TIN) and 3D wireframe to derive 3D roughness parameters are described. Thirty-eight sets of fresh rock blocks with fractures in the middle were prepared and tested in direct shear. Based on these, empirical equations for JRC estimation using 3D roughness parameters have been derived. Nine parameters (θs, θg, θ2s, SsT, SsF, Van, Zsa, Zrms, and Zrange) are found to have close correlations with JRC and are capable of estimating JRC of rock fracture surfaces. Other parameters (Zss, Zsk, Vsvi, Vsci, Sdr and Sts) show no good correlations with JRC. The sampling interval has little influence when using volume and amplitude parameters (Van, Zsa, Zrms, and Zrange) for JRC estimation, while it influences to some extent when other parameters (θs, θg, θ2s, SsT and SsF) are used. For their easy calculation, the equations with amplitude parameters are recommended to facilitate rapid estimation of JRC in engineering practice.
Highlights
The rock joint roughness coefficient (JRC) was proposed by Barton (1973) to estimate the peak shear strength of joints using the following empirical equation, which is called the JRC-JCS model:τ 1⁄4 σtan 1⁄2JRClog ðJCS=σÞ þ φbð1Þ where τ is the peak shear strength of the rock joint, σ is the normal stress, JRC is the joint roughness coefficient, JCS is the strength of joint wall, and φb is the basic friction angle.Measurement and estimation of the JRC is critical for using the JRC-JCS model and a difficult challenge in the field of rock mechanics (Barton and Bandis 1990)
Where τ is the peak shear strength of the rock joint, σ is the normal stress, JRC is the joint roughness coefficient, JCS is the strength of joint wall, and φb is the basic friction angle
This approach has been adopted by the ISRM (International Society for Rock Mechanics) Commission on Testing Methods since 1981 (Brown, 1981)
Summary
The rock joint roughness coefficient (JRC) was proposed by Barton (1973) to estimate the peak shear strength of joints using the following empirical equation, which is called the JRC-JCS model:τ 1⁄4 σtan 1⁄2JRClog ðJCS=σÞ þ φbð1Þ where τ is the peak shear strength of the rock joint, σ is the normal stress, JRC is the joint roughness coefficient, JCS is the strength of joint wall, and φb is the basic friction angle.Measurement and estimation of the JRC is critical for using the JRC-JCS model and a difficult challenge in the field of rock mechanics (Barton and Bandis 1990). Amplitude parameters (Rz, λ and Dh–L) show a lower sensitivity to the sampling interval (SI) than slope (Z2, β100%, and σI) and elongation parameters (δ) in the determination of two-dimensional (2D) JRC (Li et al 2016; Zheng and Qi 2016; Liu et al 2017) Correlations between these parameters and JRC can be found in Tse and Cruden (1979), Yu and Vayssade (1991), Wakabayashi and Fukushige (1992), Tatone and Grasselli (2010), and Zhang et al (2014), and in the reviews by Li and Zhang (2015), Li and Huang (2015), and Zheng and Qi (2016). There are no welldeveloped methods to achieve roughness parameters for the entire fracture surface and no reliable equations for estimating JRC with such parameters
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