Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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An Evaluation of Allowable Bearing Capacity of Weathered Rock by Large-Scale Plate-Bearing Test and Numerical Analysis

대형평판재하시험 및 수치해석에 의한 풍화암 허용지지력 평가

  • 홍승현 (경기대학교 토목공학과)
  • Received : 2022.09.29
  • Accepted : 2022.10.11
  • Published : 2022.10.31
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Abstract

Considering that the number of cases in which a structure foundation is located on weathered rock has been increasing recently, for adequate design bearing capacity of a foundation on weathered rock, allowable bearing capacities of such foundations in geotechnical investigation reports were studied. With reference to the study results, the allowable bearing capacity of a foundation on weathered rock was approximately 400-700 kN/m2, with a large variation, and was considered a conservative value. Because the allowable bearing capacity of the foundation ground is an important index in determining the foundation type in the early design stage, it can have a significant influence on the construction cost and period according to the initial decision. Thus, in this study, six large-scale plate-bearing tests were conducted on weathered rock, and the bearing capacity and settlement characteristics were analyzed. According to the test results, the bearing capacities from the six tests exceeded 1,500 kN/m2, and it shows that the results are similar with the one of bearing capacity formula by Pressuremeter tests when compared with the various bearing capacity formula. In addition, the elastic modulus determined by the inverse calculation of the load-settlement behavior from the large-scale plate-bearing tests was appropriate for applying the elastic modulus of the Pressuremeter tests. With consideration of the large-scale plate-bearing tests in this study and other results of plate-bearing tests on weathered rock in Korea, the allowable bearing capacity of weathered rock is evaluated to be over 1,000 kN/m2. However, because the settlement of the foundation increases as the foundation size increases, the allowable bearing capacity should be restrained by the allowable settlement criteria of an upper structure. Therefore, in this study, the anticipated foundation settlements along the foundation size and the thickness of weathered rocks have been evaluated by numerical analysis, and the foundation size and ground conditions, with an allowable bearing capacity of over 1,000 kN/m2, have been proposed as a table. These findings are considered useful in determining the foundation type in the early foundation design.

최근 구조물 기초가 풍화암상에 위치하는 경우가 증가하는 추세로 풍화암상 기초의 적정 설계 지지력을 평가하고자 국내 지반조사서상 제안된 풍화암 기초 허용 지지력을 조사하였다. 조사 결과 몇몇 현장에 제안된 풍화암 허용 지지력은 약 400~700kN/m2 수준으로 그 편차가 큰 편이며 보수적인 값으로 판단되었다. 지반의 기초 허용 지지력은 설계 초기 기초 형식 결정에 중요한 지표로, 그 결정에 따라 공사비 및 공기에 큰 영향을 줄 수 있다. 이에 본 연구에서는 적정한 풍화암 지반의 허용지지력을 평가하고자 풍화암 지반에 대하여 총 6회의 대형 평판재하시험을 실시하고 지지력 및 침하 특성을 분석하였다. 시험 결과 지지력은 모두 1,500kN/m2이상으로 평가되었으며 기존 지지력 공식과 비교하였을 때 공내재하시험에 의한 지지력 평가식이 본 시험결과와 유사함을 확인하였다. 또한 대형 평판재하시험의 하중-침하 거동 역산에 의한 지반의 탄성계수는 공내재하시험의 탄성계수(E) 값 적용이 적절하다고 평가되었다. 본 연구에서의 대형 평판재하시험 결과 및 국내 타 현장에서의 평판재하시험 사례 등을 종합하여 볼 때 풍화암 허용 지지력은 1,000kN/m2 이상으로 평가된다. 그러나 기초 침하량은 기초 크기 증가에 따라 비례하므로 구조물 허용 침하량 기준에 따라 허용 지지력은 제한되어야 한다. 따라서 본 연구에서는 수치해석적 방법으로 기초 크기 및 풍화암 두께에 따른 기초 예상 침하량을 평가하였으며, 풍화암 지반상 기초 허용지지력이 1,000kN/m2 이상일 수 있는 기초 크기 및 지반 조건을 표로 제안하였다. 이는 기초 설계 초기 기초 형식 결정에 유용하다고 사료된다.

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References

  1. Bowles, J. E. (1997), "Foundation Analysis and Design", 5th edition, The McGraw-Hill, pp.339.
  2. Canadian Geotechnical Society, (2006), "Canadian Foundation Engineering Manual", 4th edition, pp.180.
  3. Choi, Y. K., Kim, S. H., and Lee, M. H. (2009), "The Case Studies on Application of Mat Foundation System to Building Structure Founded on Weathered Ground", J. of the Korean Geotechnical Society, Vol.10, No.6, pp.5-18.
  4. Jung, H.Y. (2013), "A Study on the Bearing Capacity of Spread Foundation on Weathered Rock", Busan National Univ., pp.61-101.
  5. Kim, D. E. and Huh, K. H. (2005), "Bearing Capacity and Settlement Characteristics of Weathered Granite Masses in Gyeonggi Area", J. of the Korean Society of Hazard Mitigation, Vol.5, No.4, pp. 37-47.
  6. Kim, K.S., Lee, S.R., Park, Y.H., and Kim, S.H. (2012), "Evaluation of Size Effects of Shallow Foundation Settlement Using Large Scale Plate Load Test", J. of the Korean Geotechnical Society, Vol.28, No.7, pp.67-75. https://doi.org/10.7843/KGS.2012.28.7.67
  7. Korean Geotechnical Society (1994), "Shallow Foundation", pp.122.
  8. Korean Geotechnical Society (2018), "Structure Foundation Design Standard", pp.171-274.
  9. Lee, S. H., Yoo, B. S., and Chung, C. K. (2017), A Case Study on Geotechnical Properties and Weathering Degree of Weathered Granite Rock, J. of the Korean Geotechnical Society, Vol.33, No.12, pp.127-139. https://doi.org/10.7843/KGS.2017.33.12.127
  10. Ministry of Land, Infrastructure and Transport (2000), "Road Design Manual", pp.402.
  11. Park, C. S. and Kim, J. H. (2012), "Bearing Capacity Characteristics of Shallow Foundation by Three Dimension FEM", J. of the Korean Society of Hazard Mitigation, Vol.35, No.3, pp.17-24.
  12. Saegil ENC. (2010), "Geotechnical Report of Gyeonggi-do Goyang-si ○○○ Project", pp.51-54.
  13. Saegil ENC. (2020), "Geotechnical Report of Gyeongsangbuk-do Pohang-si ○○○ Project", pp.46-60.
  14. Sanha ENC. (2009), "Geotechnical Report of Chungcheongnam-do Sejong-si ○○○ Project", pp.192-194.
  15. Seoul Metropolitan Government (2006), "Geotechnical Investigation Manual", pp.17.
  16. Sower, G. F. (1962), "Shallow Foundation", Foundation Engineering, G. A. Leonards(ed), McGraw-Hill, pp.525.
  17. S-tech consulting group (2011), "Geotechnical Report of Gangwon-do Chuncheon-si ○○○ Project", pp.47-63.
  18. Sunwoo ENC. (2021), "Geotechnical Report of Chungcheongnam-do Asan-si Bebang ○○○ Project", pp.96-105.
  19. Taechang ENC. (2020), "Geotechnical Report of Chungcheongnam-do Asan-si ○○○ Project", pp.31-40.
  20. The British Geotechnical Association, (2012), "ICE Manual of Geotechnical Engineering", Vol.2, pp.749.