• Title, Summary, Keyword: Barton의 수정식

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Anisotropic Shear Strength of Artificially Fractured Rock Joints Under Low Normal Stress (낮은 수직응력 하에서 인공 절리면의 전단 이방성에 관한 연구)

  • 곽정열;이상은;임한욱
    • 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.

Characterization of the Three Dimensional Roughness of Rock Joints and Proposal of a Modified Shear Strength Criterion (암석 절리의 3차원 거칠기 특성화와 수정 전단강도 관계식의 제안)

  • Jang, Bo-An;Kim, Tae-Ho;Jang, Hyun-Sick
    • 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.

Estimation of Joint Roughness Coefficient(JRC) using Modified Divider Method (수정 분할자법을 이용한 절리 거칠기 계수(JRC)의 정량화)

  • Jang Hyun-Shic;Jang Bo-An;Kim Yul
    • 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.