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Case Study

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

직접전단시험에 의한 석회암 자연절리면의 전단특성 분석사례

Jong-Woo Kim1*
김 종우1*
1Dept. of Civil Engineering, Cheongju University
1청주대학교 토목공학과
* Corresponding Author
31 October 2019. pp. 292-304
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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°, residual friction angle of 38° and cohesion of 37 kPa.

Keywords
Rock joint
Limestone
Roughness
Individual direct shear test
Multi-stage direct shear test

완만한 거칠기를 갖는 석회암 자연절리면에 대하여 KSRM 표준시험법에 의거한 개별적 직접전단시험과 수직응력을 단계별로 조절하는 다단계 직접전단시험을 실시하였다. 각 시험을 통해 전단시험 전후의 절리면 거칠기 변화를 알아보았고, 두 가지 시험에서 얻은 전단특성 값의 차이를 분석하였다. 두 가지 시험에서 모두 절리면의 거칠기가 클수록 전단저항은 증가하였으며, 수직응력이 증가할수록 절리면의 전단에 필요한 최대전단응력 값은 증가하였다. 다단계 직접전단시험으로 구한 최대마찰각은 개별적 직접전단시험으로 구한 것의 63% 수준에 불과하였다. 다단계시험은 절리면 요철부의 초기 맞물림이 단계적인 전단과정에 따라 시험 중 수시로 변화되어 원래의 거칠기가 변형되기 때문에 암석 절리면의 마찰각을 구할 때는 개별적 직접전단시험이 더 유효한 방법으로 판단된다. JRC값 4~8의 완만한 거칠기를 갖는 석회암 절리면의 물성값은 최대마찰각 47°, 잔류마찰각 38°, 점착력 37 kPa으로 평가되었다.

키워드
절리면
석회암
거칠기
개별적 직접전단실험
다단계 직접전단시험
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Information
  • Publisher :Korean Society for Rock Mechanics and Rock Engineering
  • Publisher(Ko) :한국암반공학회
  • Journal Title :Tunnel and Underground Space
  • Journal Title(Ko) :터널과 지하공간
  • Volume : 29
  • No :5
  • Pages :292-304
  • Received Date : 2019-09-25
  • Revised Date : 2019-10-14
  • Accepted Date : 2019-10-17
  • DOI :https://doi.org/10.7474/TUS.2019.29.5.292
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