Journal of the Korean GEO-environmental Society (한국지반환경공학회 논문집)

Korean Geo-Environmental Society (한국지반환경공학회)
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Evaluation of Vertical Bearing Capacity for Bucket and Shallow Foundations Installed in Sand

사질토 지반에 설치된 버킷기초 및 얕은기초의 수직지지력 산정

  • Park, Jeongseon (Department of Civil and Environmental Engineering, Hanyang University) ;
  • Park, Duhee (Department of Civil and Environmental Engineering, Hanyang University) ;
  • Jee, Sunghyun (R&D Division, Hyundai E&C Co., Ltd.) ;
  • Kim, Dongjoon (R&D Division, Hyundai E&C Co., Ltd.)
  • Received : 2015.07.06
  • Accepted : 2015.07.22
  • Published : 2015.09.01
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Abstract

The vertical bearing capacity of a bucket foundation installed in sand can be calculated as sum of the skin friction and end bearing capacity. However, the current design equations are not considering the non-associated flow characteristics of sand and the reduction in the skin friction and increase in the end bearing capacity when the vertical load is applied. In this study, we perform two-dimensional axisymmetric finite element analyses following non-associated flow rule and calculate the vertical bearing capacity of circular bucket foundation of various sizes installed in sand of different friction angles. After calculating the skin friction and end bearing force at the ultimate state, design equations are derived for each. The skin friction of bucket foundation is shown significantly small compared to the end bearing capacity. Considering the difference with the available design equation for piles, it is recommended that the equation for piles is used for the bucket foundation. A new shape-depth factor ($s_q{\cdot}d_q$) for bucket foundation is recommended which also accounts for the increment of the end bearing capacity due to skin friction. Additionally, the shape and depth factor of embedded foundation proposed from the associated flow rule can overestimate the bearing capacity in sand, so it is more adequate to use the shape-depth factor proposed in this study.

사질토 지반에 설치된 버킷기초의 수직지지력은 주면마찰력과 선단지지력의 합으로 산정할 수 있다. 하지만 수직하중 작용 시 나타나는 주면마찰력 감소와 선단지지력 증가의 특징을 정확하게 고려할 수 있는 설계식이 없으며, 실제와 같은 사질토 지반의 비관련흐름 특성이 반영되어야 한다. 본 연구에서는 2차원 축대칭 유한요소해석으로 사질토 지반에 설치된 원형 버킷기초의 수직지지력을 다양한 지반 마찰각과 기초 크기에 대하여 산정하였다. 해석 결과의 극한지지력을 주면마찰력과 선단지지력으로 분리하여 특징을 분석한 후 각각의 설계식을 도출하였다. 버킷기초의 주면마찰력은 선단지지력에 비해 크기가 매우 작고 말뚝 설계식과 차이가 근소하므로 이를 동일하게 사용하였다. 주면마찰력의 영향으로 얕은기초의 지지력보다 증가하는 버킷기초의 선단지지력은 기존의 설계식을 수정하여 적용할 수 있도록 해석 결과를 토대로 새로운 형상-깊이계수($s_q{\cdot}d_q$)를 제안하였다. 또한 관련흐름법칙을 적용하여 제안된 기존의 얕은기초 형상계수와 깊이계수는 실제 사질토 지반에서의 지지력을 과대예측하므로 비관련흐름 특성을 반영한 형상-깊이계수를 사용하여 지지력을 예측해야 한다.

Keywords

References

  1. Achmus, M., Akdag, C. T. and Thieken, K. (2013), Load-bearing behavior of suction bucket foundations in sand, Applied Ocean Research, Vol. 43, pp. 157-165. https://doi.org/10.1016/j.apor.2013.09.001
  2. Bang, S. and Cho, Y. (2001), Ultimate vertical loading capacity of suction piles, 36th Annual Symposium on Engineering Geology and Geotechnical Engineering, Las Vegas, NV, pp. 703-712.
  3. Bang, S. and Cho, Y. (2002), Ultimate horizontal loading capacity of suction piles, International Journal of Offshore and Polar Engineering, Vol. 12, No. 1, pp. 56-63.
  4. Benmebarek, S., Remadna, M. S., Benmebarek, N. and Belounar, L. (2012), Numerical evaluation of the bearing capacity factor $N_{\gamma}$ of ring footings, Computers and Geotechnics, Vol. 44, pp. 132-138. https://doi.org/10.1016/j.compgeo.2012.04.004
  5. Bransby, F. and Randolph, M. (1999), The effect of embedment depth on the undrained response of skirted foundations to combined loading, Soil and Foundations, Vol. 39, No. 4, pp. 19-33. https://doi.org/10.3208/sandf.39.4_19
  6. Bransby, M. F. and Yun, G. J. (2009), The undrained capacity of skirted strip foundations under combined loading, Geotechnique, Vol. 59, No. 2, pp. 115-125. https://doi.org/10.1680/geot.2007.00098
  7. Brinkgreve, R. B. J. and Vermeer, P. A. (1999), Plaxis: finite element code for soil and rock analyses: version 7, Balkema, pp. 1-376.
  8. Byrne, B. W. and Cassidy, M. J. (2002), Investigating the response of offshore foundations in soft clay soils, ASME 2002 21st International Conference on Offshore Mechanics and Arctic Engineering: American Society of Mechanical Engineers, pp. 263-275.
  9. Caquot, A. and Kerisel, J. (1953), Sur le terme de surface dans le calcul des fondations en milieu pulverulent, Proceedings of the third international conference on soil mechanics and foundation engineering, Zurich, pp. 336-337.
  10. Cho, Y. and Bang, S. (2002), Inclined loading capacity of suction piles, Proceedings of 12th International Offshore and Polar Engineering Conference, Japan, Paper, pp. 827-832.
  11. Eid, H. T. (2013), Bearing capacity and settlement of skirted shallow foundations on sand, International Journal of Geomechanics, Vol. 13, No. 5, pp. 645-652. https://doi.org/10.1061/(ASCE)GM.1943-5622.0000237
  12. Erickson, H. L. and Drescher, A. (2002), Bearing capacity of circular footings, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 128, No. 1, pp. 38-43. https://doi.org/10.1061/(ASCE)1090-0241(2002)128:1(38)
  13. Frydman, S. and Burd, H. J. (1997), Numerical studies of bearing-capacity factor $N_{\gamma}$, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 123, No. 1, pp. 20-29. https://doi.org/10.1061/(ASCE)1090-0241(1997)123:1(20)
  14. Gourvenec, S. (2008), Effect of embedment on the undrained capacity of shallow foundations under general loading, Geotechnique, Vol. 58, No. 3, pp. 177-185. https://doi.org/10.1680/geot.2008.58.3.177
  15. Hansen, J. B. (1970), A revised and extended formula for bearing capacity, Akademiet for de Tekniske Videnskaber, Geoteknisk Institut, Vol. 28, pp. 5-11.
  16. Houlsby, G. T., Ibsen, L. B. and Byrne, B. W. (2005), Suction caissons for wind turbines, Frontiers in Offshore Geotechnics: ISFOG, Perth, WA, Australia, pp. 75-93.
  17. House, A., Randolph, M. and Borbas, M. (1999), Limiting aspect ratio for suction caisson installation in clay, Proceedings of the 9th International Offshore and Polar Engineering Conference (ISOPE 99), Brest, 30, pp. 676-683.
  18. House, A. R. and Randolph, M. F. (2001), Installation and pull-out capacity of stiffened suction caissons in cohesive sediments, Proceedings of the 11th International Offshore and Polar Engineering Conference, 2, pp. 574-580.
  19. Hung, L. C. and Kim, S. R. (2012), Evaluation of vertical and horizontal bearing capacities of bucket foundations in clay, Ocean Engineering, Vol. 52, pp. 75-82. https://doi.org/10.1016/j.oceaneng.2012.06.001
  20. Hung, L. C. and Kim, S. R. (2014), Evaluation of undrained bearing capacities of bucket foundations under combined loads, Marine Georesources & Geotechnology, Vol. 32, No. 1, pp. 76-92. https://doi.org/10.1080/1064119X.2012.735346
  21. Itasca (2011), FLAC, Fast lagrangian analysis of continua, Minneapolis, pp. 1-3058.
  22. Kim, D. J., Youn, J. U., Jee, S. H., Choi, J., Lee, J. S. and Kim, D. S. (2014), Numerical studies on Bearing capacity factor $N_{\gamma}$ and Shape Factor of Strip and Circular Footings in Sand According to Dilatancy Angle, Journal of the Korean Geotechnical Society, Vol. 30, No. 1, pp. 49-63 (in Korean). https://doi.org/10.7843/kgs.2014.30.1.49
  23. Loukidis, D. and Salgado, R. (2009), Bearing capacity of strip and circular footings in sand using finite elements, Computers and Geotechnics, Vol. 36, No. 5, pp. 871-879. https://doi.org/10.1016/j.compgeo.2009.01.012
  24. Lyamin, A. V., Salgado, R., Sloan, S. W. and Prezzi, M. (2007), Two-and three-dimensional bearing capacity of footings in sand, Geotechnique, Vol. 57, No. 8, pp. 647-662. https://doi.org/10.1680/geot.2007.57.8.647
  25. Martin, C. M. (2005), Exact bearing capacity calculations using the method of characteristics, Proc. IACMAG. Turin, pp. 441-450.
  26. Meyerhof, G. G. (1963), Some recent research on the bearing capacity of foundations, Canadian Geotechnical Journal, Vol. 1, No. 1, pp. 16-26. https://doi.org/10.1139/t63-003
  27. Park, J. S., Park, D., Yoon, S. W. and Jang, H. S. (2015), Vertical load transfer mechanism of bucket foundation in sand, Journal of the Korean Geotechnical Society, Vol. 31, No. 7, pp. 29-39 (in Korean). https://doi.org/10.7843/kgs.2015.31.7.29
  28. Prandtl, L. (1920), Uber die harte plastischer korper, Nachrichten von der Gesellschaft der Wissenschaften zu Gottingen, Mathematisch-Physikalische Klasse, Vol. 1920, pp. 74-85.
  29. Reissner, H. (1924), Zum erddruckproblem, Proc. 1st Int. Congress for Applied Mechanics: Delft, pp. 295-311.
  30. Salgado, R. (2008), The engineering of foundations, McGraw Hill New York, pp. 1-882.
  31. Simulia (2010), Abaqus user's manual, Dassault Systemes Simulia Corp., pp. 1-773.
  32. Terzaghi, K. (1943), Theoretical soil mechanics, Wiley New York, pp. 1-510.
  33. Tjelta, T. I. (2001), Suction piles: their position and applications today, Proceedings of the 11th International Offshore and Polar Engineering Conference, Stavanger, Norway, June, pp. 17-22.
  34. Vesic, A. S. (1973), Analysis of ultimate loads of shallow foundations, Journal of the Soil Mechanics and Foundations Division, Vol. 99, No. 1, pp. 54-73.
  35. Vesic, A. S. (1975), Bearing capacity of shallow foundations, Foundation Engineering Handbook., pp. 121-147.
  36. Yun, G. and Bransby, M. F. (2007), The undrained vertical bearing capacity of skirted foundations, Soil and Foundations, Vol. 47, No. 3, pp. 493-505. https://doi.org/10.3208/sandf.47.493