• Tunnel and Underground Space
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• v.13 no.3
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• pp.169-179
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• 2003

Anisotropic shear strength of rock joints is studied based on the artificially fractured specimens using experimental and analytical methods. Series of direct shear tests are performed to obtain the strength, stiffness and friction angle of joints under various low normal stresses and shearing directions. The results of shear strength and stiffness show anisotropic value according to shearing direction under low normal stress specially less than 2.45 MPa. But, the effect of joint roughness on strength decreases with increasing normal stress. To estimate more effectively the peak shear strength under low normal stress, the modified Barton's equation is suggested.

• The Journal of Engineering Geology
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• v.20 no.3
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• pp.319-327
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• 2010

Surface roughness profiles were measured from 19 joint samples using a laser scanner, and Joint Roughness Coefficient (JRC) values were calculated from 30 sections in each sample. Although JRC values varied with the location of the section, the average JRC values from any three sections provides an adequate representation of the average JRC value for the entire surface well. Direct shear tests were performed on nine joints reproduced using molds of real joints in samples of gypsum. The peak friction angles (${\phi}_p$) showed a linear relationship with the average JRC values, yielding the following relationship: ${\phi}_p=41.037+1.046JRC$. However, the shear strengths measured by direct shear tests differed from those calculated using Barton's criterion. The relationship between calculated from direct shear tests and JRC measured from joint surfaces is defined as $JRC_R=f{\cdot}JRC$, and the correction coefficient f is was calculated as $f=3.15JRC^{-0.5}$, as calculated by regression. A modified shear-strength criterion, is proposed using the correction coefficient, ${\tau}={\sigma}_n{\cdot}tan(3.15JRC^{0.5}{\bullet}{\log}_{10}\frac{JCS}{{\sigma}_n}+{\phi}_b)$. This criterion may be effective in calculating the shear strength of moderately weathered rock joints and highly weathered rock joints with low strength and ductile behavior.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.561-577
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• 2021

The ten standard roughness profiles suggested by Barton and Choubey (1977) were extended to make three-dimensional (3D) joint models whose profiles were identical at any cross section. Replicas of joint models were produced using plaster of Paris, and direct shear tests were performed to verify the joint roughness coefficients (JRC) of the standard roughness profiles. Joint shear strengths measured by direct shear tests were compared with those predicted by the shear failure criterion suggested by Barton (1973) based on JRC, joint compressive strength (JCS), and joint basic friction angle (𝜙_b). Shear strengths measured from joints of the first and fourth standard roughness profiles were close to predicted values; however, shear strengths measured from the other joint models were lower than predicted, the differences increasing as the roughness of joints increased. Back calculated values for JRC, JCS, and from the results of the direct shear tests show measured shear strengths were lower than predicted shear strengths because of the JRC values. New JRC were back calculated from the measured shear strength and named JRC_m. Values of JRC_m were lower than the JRC for the standard roughness profiles but show a strong linear relationship to JRC. Corrected JRC_m values for the standard roughness profiles are provided and revised relationships between JRC_m and JRC, and new shear strength criterion are suggested.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.269-280
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• 2005

We assigned points on surface of standard roughness profile by 0.1mm along the length and measured coordinates of points. Then, the lengths of profile were measured with different scales using modified divider method. The fractal dimensions and intercepts of slopes were determined by plotting the length vs scale in log-log scale. The fractal dimensions as well as intercepts of slopes show well correlation with joint roughness coefficients(JRC). However, multiplication of the kactal dimension by intercept show better correlation with IRC and we derived a new equation to estimate JRC from fractal dimension and intercept. The crossover length in which we can determine the correct fractal dimension was between 0.3-3.2mm. We measured joint roughness of 26 natural joints and calculated JRC using the equation suggested by Tse and Cruden(1979) and new equation derived by us. IRC values calculated by both equations are almost the same, indicating new equation is effective in measuring IRC.