Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Probabilistic Analysis for Rock Slope Stability Due to Weathering Process

풍화작용에 따른 암반사면 안정성의 확률론적 해석

  • Park, Hyuck-Jin (Dept. of Geoinformation Engineering, Sejong University) ;
  • Woo, Ik (Dept. of Coastal Construction Engineering, Kunsan National University) ;
  • Um, Jeong-Gi (Dept. of Energy Resources Engineering, Pukyong National University)
  • 박혁진 (세종대학교 지구정보공학과) ;
  • 우익 (군산대학교 해양건설공학과) ;
  • 엄정기 (부경대학교 에너지자원공학과)
  • Published : 2009.08.28
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Abstract

Since weathering weakens the rock fabric and exaggerates any structural weakness, it affects mechanical properties as well as physical and chemical properties of rock. Weathering leads to a decrease in density, strength, friction angle and cohesion, and subsequently it affects negatively on the stability of rock slope. The purpose of the study is to investigate the changes of the rock slope stability caused by discontinuities which have different weathering grades. For that, the discontinuity samples which are divided into two different weathering grades are obtained from the field and tested their mechanical properties such as JCS, JRC and residual friction angle. In order to evaluate the effects on the stability of slope due to weathering, the deterministic analysis is carried out. That is, the factors of safety for planar failure are calculated for rock masses which have two different weathering grades, such as fresh and weathered rock mass. However, since the JRC and friction angle values are widely scattered and the deterministic analysis cannot consider the variation, the factors of safety cannot represent properly the stability of the rock slope. Therefore, the probabilistic analysis has been used to consider the scattered values. In the deterministic analysis, the factors of safety for the fresh discontinuity and weathered discontinuity are 1.25 and 1.0, respectively. The results indicate the fresh discontinuities are stable for planar failure and the weathered discontinuities are marginally stable. However, the probabilities of failure for the fresh discontinuity and weathered discontinuity are 25.6% and 45.9%, respectively. This shows that both discontinuities are analyzed as unstable in the probabilistic analysis.

풍화작용은 암석의 물리적 및 화학적 특성을 변화시킬 뿐만 아니라 공학적 특성에도 영향을 미친다. 대개 풍화는 암석의 밀도 및 강도, 내부마찰각과 점착력 등을 감소시키며 이로 인해 암석으로 구성된 사면의 안정성에 부정적인 영향을 미칠 수 있다. 따라서 본 연구에서는 풍화등급에 따른 암반 사면의 안정성을 분석하여 풍화가 사면의 안정성에 미치는 영향을 분석해 보았다. 이를 위하여 암반사면의 안정성에 가장 주요한 영향을 미치는 불연속면 시료를 풍화등급별로 채취하여 공학적인 특성의 변화를 분석하였다. 이러한 결과를 활용하여 신선한 암반으로 구성된 사면과 풍화된 암반으로 구성된 사면의 안전율을 산정하였다. 신선한 암반의 경우 안전율이 1.25로 안전한 것으로 분석되었으며 풍화된 암반의 경우 안전율이 1.0으로 계산되었다. 그러나 이렇게 산정된 안전율은 값의 분산이 심한 불연속면 거칠기 계수(JRC)와 잔류마찰각에 따라 심하게 변동되고 있어 안전율로 사면의 안정성을 정확하게 파악하기 힘든 실정이다. 따라서 본 연구에서는 불연속면 거칠기 계수(JRC)와 잔류마찰각이 일정한 범위 내에 분포한다는 점에 착안하여 확률변수로 고려하였으며 확률론적 해석을 수행하였다. 확률론적 해석 결과 신선한 암반에서의 파괴확률은 25.6%로 계산되어 매우 불안정한 것으로 파악되었으며 풍화된 암반의 경우는 45.9%의 파괴확률이 획득되었다. 현장으로부터 획득된 자료들의 분산으로 인해 결정론적 해석기법은 사면의 안정성을 평가하는 데 부적절한 것으로 판단된다.

Keywords

References

  1. Barton, N. (1973) Review of a new shear strength criterion for rock joints. Engineering Geology, v. 7, p. 287-332 https://doi.org/10.1016/0013-7952(73)90013-6
  2. Barton, N. and Choubey, V. (1977) The shear strength of rock joints in theory and practice. Rock Mechanics, v. 10, p. 1-54 https://doi.org/10.1007/BF01261801
  3. Bell, F. G. (2007) Engineering Geology, 2nd Ed. Butterworth- Heinemann, p. 581
  4. Chorley, R. J. (1969) The role of water in rock disintegration, Introduction to Fluvial Processes, Methuen, p. 53-73
  5. G.S.E.G. (1995) Geological Society Engineering Group Working Party Report: The description and classification of weathered rocks for engineering purposes. Quarterly Journal of Engineering Geology, v. 283, p. 207-242
  6. Hoek, E.T. (1998) Factor of safety and probability of failure. Course notes, Internet edition. http://www.rockeng.utoronto.ca/hoekcorner.htm
  7. Kulatilake, P.H.S.W., Shou, G., Huang, T.H. and Morgan, R.M. (1995) New peak shear strength criteria for anisotropic rock joints. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstract, v. 32, p. 673-697 https://doi.org/10.1016/0148-9062(95)00022-9
  8. Lee, S. G. and De Freitas, M. H. (1989) A revision of the description and classification of weathered granite and its application to granites in Korea. Quarterly Journal of Engineering Geology v. 22, p. 31-48 https://doi.org/10.1144/GSL.QJEG.1989.022.01.03
  9. Mostyn, G.R. and Li, K.S. (1993) Probabilistic slope analysis- state of play. Proceedings of Conference on Probabilistic Methods in Geotechnical Engineering. A.A. Balkema, p. 89-109
  10. Nilsen, B. (2000) New trend in rock slope stability analysis. Bull. Eng. Geol. Environ. v. 58, p. 173-178 https://doi.org/10.1007/s100640050072
  11. Park, H.J. and West, T.R. (2001) Development of a probabilistic approach for rock wedge failure. Eng. Geol. v. 59, p. 233-251 https://doi.org/10.1016/S0013-7952(00)00076-4
  12. Park, H.J., West, T.R. and Woo, I. (2005) probabilistic analysis of rock slope stability and random properties of discontinuity parameters, I-40, Western North Carolina, USA. Eng. Geol. v. 79, p. 230-250 https://doi.org/10.1016/j.enggeo.2005.02.001
  13. Pathak, S. and Nilsen, B. (2004) Probabilistic rock slope stability analysis for Himalayan condition. Bull. Eng. Geol. Environ. v. 63, p. 25-32 https://doi.org/10.1007/s10064-003-0226-1
  14. Price, D.G. (1995) Weathering and weathering processes, Quarterly Journal of Engineering Geology, v. 28, p. 243-252 https://doi.org/10.1144/GSL.QJEGH.1995.028.P3.03
  15. Price, D.G. (2009) Engineering Geology; Principles and Practice, Springer, p. 450
  16. Um, J.G., W. I., and Park, H.J. (2009) Variation of engineering geological characteristics of Jurassic Granite in Wonju due to freeze thaw weathering. Eco. Environ. Geol. v. 42, p. 261-272
  17. Yu, X. and Vayssade, B. (1991) Joint Profiles and their Roughness Parameters. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstract, v. 28, p. 333-336 https://doi.org/10.1016/0148-9062(91)90598-G