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Influence of Microcrack on Brazilian Tensile Strength of Jurassic Granite in Hapcheon

미세균열이 합천지역 쥬라기 화강암의 압열인장강도에 미치는 영향

  • Park, Deok-Won (Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Kim, Kyeong-Su (Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources)
  • 박덕원 (한국지질자원연구원 지질환경연구본부) ;
  • 김경수 (한국지질자원연구원 지질환경연구본부)
  • Received : 2021.01.14
  • Accepted : 2021.03.17
  • Published : 2021.03.31

Abstract

The characteristics of the six rock cleavages(R1~H2) in Jurassic Hapcheon granite were analyzed using the distribution of ① microcrack lengths(N=230), ② microcrack spacings(N=150) and ③ Brazilian tensile strengths(N=30). The 18 cumulative graphs for these three factors measured in the directions parallel to the six rock cleavages were mutually contrasted. The main results of the analysis are summarized as follows. First, the frequency ratio(%) of Brazilian tensile strength values(kg/㎠) divided into nine class intervals increases in the order of 60~70(3.3) < 140~150(6.7) < 100~110·110~120(10.0) < 90~100(13.3) < 80~90(16.7) < 120~130·130~140(20.0). The distribution curve of strength according to the frequency of each class interval shows a bimodal distribution. Second, the graphs for the length, spacing and tensile strength were arranged in the order of H2 < H1 < G2 < G1 < R2 < R1. Exponent difference(λS-λL, Δλ) between the two graphs for the spacing and length increases in the order of H2(-1.59) < H1(-0.02) < G2(0.25) < G1(0.63) < R2(1.59) < R1(1.96)(2 < 1). From the related chart, the six graphs for the tensile strength move gradually to the left direction with the increase of the above exponent difference. The negative slope(a) of the graphs for the tensile strength, suggesting a degree of uniformity of the texture, increases in the order of H((H1+H2)/2, 0.116) < G((G1+G2)/2, 0.125) < R((R1+R2)/2, 0.191). Third, the order of arrangement between the two graphs for the two directions that make up each rock cleavage(R1·R2(R), G1·G2(G), H1·H2(H)) were compared. The order of arrangement of the two graphs for the length and spacing is reverse order with each other. The two graphs for the spacing and tensile strength is mutually consistent in the order of arrangement. The exponent differences(ΔλL and ΔλS) for the length and spacing increase in the order of rift(R, -0.08) < grain(G, 0.14) < hardway(H, 0.75) and hardway(H, 0.16) < grain(G, 0.23) < rift(R, 0.45), respectively. Fourth, the general chart for the six graphs showing the distribution characteristics of the microcrack lengths, microcrack spacings and Brazilian tensile strengths were made. According to the range of length, the six graphs show orders of G2 < H2 < H1 < R2 < G1 < R1(< 7 mm) and G2 < H1 < H2 < R2 < G1 < R1(≦2.38 mm). The six graphs for the spacing intersect each other by forming a bottleneck near the point corresponding to the cumulative frequency of 12 and the spacing of 0.53 mm. Fifth, the six values of each parameter representing the six rock cleavages were arranged in the order of increasing and decreasing. Among the 8 parameters related to the length, the total length(Lt) and the graph(≦2.38 mm) are mutually congruent in order of arrangement. Among the 7 parameters related to the spacing, the frequency of spacing(N), the mean spacing(Sm) and the graph (≦5 mm) are mutually consistent in order of arrangement. In terms of order of arrangement, the values of the above three parameters for the spacing are consistent with the maximum tensile strengths belonging to group E. As shown in Table 8, the order of arrangement of these parameter values is useful for prior recognition of the six rock cleavages and the three quarrying planes.

① 미세균열의 길이(N=230), ② 미세균열의 간격(N=150) 및 ③ 압열인장강도(N=30)를 이용하여 쥬라기의 합천화강암에서 발달된 여섯 결(R1~H2)의 특성을 분석하였다. 여섯 결에 평행한 방향으로 측정한 이들 세 인자에 대한 18개의 누적그래프를 상호 대비하였다. 분석한 주요 결과를 요약하면 다음과 같다. 첫째, 9개 계급구간으로 구분한 압열인장강도값(kg/㎠)의 분포율(%)은 60~70(3.3) < 140~150(6.7) < 100~110·110~120(10.0) < 90~100(13.3) < 80~90(16.7) < 120~130·130~140(20.0)의 순으로 증가한다. 각 계급구간의 빈도수에 따른 강도의 분포곡선은 이봉 분포를 보여 준다. 둘째, 길이, 간격 및 인장강도에 대한 그래프를 H2 < H1 < G2 < G1 < R2 < R1의 순으로 배열하였다. 간격과 길이에 대한 두 그래프 사이의 지수차(λS-λL, Δλ)는 H2(-1.59) < H1(-0.02) < G2(0.25) < G1(0.63) < R2(1.59) < R1(1.96)(2 < 1)의 순으로 증가한다. 관련 도면으로부터, 상기한 지수차의 증가와 함께 인장강도에 대한 여섯 그래프는 점차 좌측 방향으로 이동한다. 조직의 균일도를 지시하는 인장강도에 대한 그래프의 음의 기울기(a)는 3번 결((H1+H2)/2, 0.116) < 2번 결((G1+G2)/2, 0.125) < 1번 결((R1+R2)/2, 0.191)의 순으로 증가한다. 셋째, 각 결(R1·R2(1번 결), G1·G2(2번 결), H1·H2(3번 결))을 구성하는 두 방향에 대한 그래프 사이의 배열순을 비교하였다. 길이와 간격에 대한 두 그래프의 배열순은 상호 역순이다. 간격과 인장강도에 대한 두 그래프는 배열순에서 서로 일관성이 있다. 길이와 간격에 대한 지수차(ΔλL 및 ΔλS)는 1번 결(R, -0.08) < 2번 결(G, 0.14) < 3번 결(H, 0.75) 및 3번 결(H, 0.16) < 2번 결(G, 0.23) < 1번 결(R, 0.45)의 순으로 각각 증가한다. 넷째, 미세균열의 길이, 미세 균열의 간격 및 인장강도의 분포 특성을 보여 주는 여섯 그래프에 대한 종합도를 작성하였다. 길이의 범위에 따라, 여섯 그래프는 G2 < H2 < H1 < R2 < G1 < R1(<7 mm) 및 G2 < H1 < H2 < R2 < G1 < R1(≦2.38 mm)의 순을 보여 준다. 간격에 대한 여섯 그래프는 누적 빈도수 12 및 간격 0.53 mm에 해당하는 지점 부근에서 병목구간을 형성하여 서로 교차한다. 다섯째, 여섯 결을 대변하는 각 파라미터의 여섯 값을 증가 및 감소하는 순으로 배열하였다. 길이와 관련된 8개 파라미터 중에서, 총 길이(Lt) 및 그래프(≦2.38 mm)는 배열순에서 상호 부합한다. 간격과 관련된 7개 파라미터 중에서, 간격의 빈도수(N), 평균 간격(Sm) 및 그래프(≦5 mm)는 배열순에서 상호 일관성이 있다. 배열순의 측면에서, 간격에 대한 상기 세 파라미터의 값은 그룹 E에 속하는 최대인장강도와 일관성이 있다. 표 8에서와 같이, 이들 파라미터 값의 배열순은 여섯 결 및 세채석면에 대한 사전 인식에 유용하다.

Keywords

References

  1. Chen, Y., Nishiyama, T., Kita, H. and Sato, T., 1997, Correlation between microfracture type and splitting planes of Inada granite and Kurihashi granodiorite. Journal of the Japan Society of Engineering Geology, 38.4, 196-204. https://doi.org/10.5110/jjseg.38.196
  2. Dai, F. and Xia, K., 2010, Loading rate dependence of tensile strength anisotropy of Barre granite. Pure and Applied Geophysics. 167, 1419-1432. https://doi.org/10.1007/s00024-010-0103-3
  3. Fujii, Y., Takemura, T., Takahashi, M., Weiren, L.I.N. and Akaiwa, S., 2005, The feature of uniaxial tensile fractures in granite and their relation to rock anisotropy. Journal of the Japan Society of Engineering Geology, 46, 227-231. https://doi.org/10.5110/jjseg.46.227
  4. Jang, B.A. and Oh, S.H., 2001, Mechanical anisotropy dependent on the rock fabric in the Pocheon granite and its relationship with microcracks. The Journal of Engineering Geology, 11, 191-203.
  5. Kim, M.K., 2015, The mechanical properties of the Geochang granite. Tunnel and Underground Space, 25, 24-36. https://doi.org/10.7474/TUS.2015.25.1.024
  6. Kudo, Y., Hashimoto, K., Sano, O. and Nakagawa, K., 1986, The empirical knowledge of quarryman and physical properties of granite. Japanese Society of Soil Mechanics and Foundation Engineering, 34, 47-51.
  7. Kudo, Y., Hashimoto, K., Sano, O. and Nakagawa, K., 1987, Relation between physical anisotropy and microstructures of granitic rock in Japan. In 6th ISRM Congress. International Society for Rock Mechanics.
  8. Lee, S.E., Cho, S.H., Seo, Y.S., Yang, H.S. and Park, H.M., 2001, The effect of microcracks on the mechanical anisotropy of granite. Material science Research International, 7, 7-13.
  9. Lin, W. and Takahashi, M., 2008, Anisotropy of strength and deformation of Inada granite under uniaxial tension. Chinese Journal of Rock Mechanics and Engineering, 27, 2463-2472. https://doi.org/10.3321/j.issn:1000-6915.2008.12.011
  10. Park, D.W., 2007, Orientations of vertical rift and grain planes in Mesozoic granites, Korea. The Journal of the Petrological Society of Korea, 16, 12-26.
  11. Park, D.W., 2011, Characteristics of the rock cleavage in Jurassic granite, Hapcheon. The Journal of the Petrological Society of Korea, 20, 219-230. https://doi.org/10.7854/JPSK.2011.20.4.219
  12. Park, D.W., 2015a, Characteristics of the rock cleavage in Jurassic granite, Geochang. The Journal of the Petrological Society of Korea, 24(3), 153-164. https://doi.org/10.7854/JPSK.2015.24.3.153
  13. Park, D.W., 2015b, Evaluation for rock cleavage using distribution of microcrack lengths. The Journal of the Petrological Society of Korea, 24(3), 165-180. https://doi.org/10.7854/JPSK.2015.24.3.165
  14. Park, D.W., 2016a, Evaluation for rock cleavage using distribution of microcrack spacings (I). The Journal of the Petrological Society of Korea, 25(1), 13-27. https://doi.org/10.7854/JPSK.2016.25.1.13
  15. Park, D.W., 2016b, Evaluation for rock cleavage using distribution of microcrack spacings (II). The Journal of the Petrological Society of Korea, 25(2), 151-163. https://doi.org/10.7854/JPSK.2016.25.2.151
  16. Park, D.W., 2016c, Evaluation for rock cleavage using distribution of microcrack spacings (III). The Journal of the Petrological Society of Korea, 25(4), 1-14. https://doi.org/10.7854/JPSK.2016.25.1.1
  17. Park, D.W., 2020a, Evaluation for rock cleavage using distributional characteristics of microcracks and Brazilian tensile strengths. Korean Journal of Mineralogy and Petrology. 33, 99-114. https://doi.org/10.22807/KJMP.2020.33.2.99
  18. Park, D.W., 2020b, Mechanical characteristics of the rift, grain and hardway planes in Jurassic granites, Korean Journal of Mineralogy and Petrology. 33, 273-291. https://doi.org/10.22807/KJMP.2020.33.3.273
  19. Park, D.W., Kim, H.C., Lee, C.B., Hong, S.S., Chang, S.W. and Lee, C.W., 2004, Characteristics of the rock cleavage in Jurassic granite, Pocheon. The Journal of the Petrological Society of Korea, 13, 133-141.
  20. Park, D.W., Seo, Y.S., Jeong, G.C. and Kim, Y.K., 2001, Microscopic analysis of the rock cleavage for Jurassic granite in Korea. The Journal of Engineering Geology, 11, 51-62.
  21. Peng, S.S. and Johnson, A.M., 1972, Crack growth and faulting in cylindrical specimens of Chelmsford granite. International Journal of Rock Mechanics and Mining, 9, 37-86. https://doi.org/10.1016/0148-9062(72)90050-2
  22. Seo, Y.S. and Park, D.W., 2003, Mechanical anisotropy of Jurassic granite in Korea. The Journal of Engineering Geology, 13, 257-266. https://doi.org/10.3969/j.issn.1004-9665.2005.02.022
  23. Zhuang, L., Diaz, M. B., Jung, S. G. and Kim, K. Y., 2016, Cleavage dependent indirect tensile strength of Pocheon granite based on experiments and DEM simulation. Tunnel and Underground Space, 26.4, 316-326. https://doi.org/10.7474/TUS.2016.26.4.316