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Case Study on the Shear Characteristics of Limestone Joint Surfaces by Direct Shear Tests

직접전단시험에 의한 석회암 자연절리면의 전단특성 분석사례

  • Kim, Jong-Woo (Dept. of Civil Engineering, Cheongju University)
  • 김종우 (청주대학교 토목공학과)
  • Received : 2019.09.25
  • Accepted : 2019.10.17
  • Published : 2019.10.31

Abstract

Limestone joint surfaces with smooth roughness were experimented by means of both the individual direct shear tests based on the KSRM standard test method and the multi-stage direct shear test to apply the stepwise vertical stresses. Changes in the roughness of the joint surfaces before and after the shear tests were examined and the difference between the two kinds of tests mentioned above was analyzed. In both tests, the shear resistance increased as the joint roughness increased and the maximum shear stress required for shearing the joint surface increased as the vertical stress increased. The peak friction angle obtained by the multi-stage direct shear tests was only 63% of that obtained by the individual direct shear tests. In the multi-stage direct shear test, the initial engagement of the concave-convex parts changes frequently during stepwise shearing process, which deforms the original roughness of a joint surface. Accordingly, the individual direct shear test is thought to be more effective when obtaining the friction angle of the rock joint surfaces. Limestone joint surfaces with smooth roughness of JRC value 4~8 were found to have peak friction angle of $47^{\circ}$, residual friction angle of $38^{\circ}$ and cohesion of 37 kPa.

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