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

Korean Geo-Environmental Society (한국지반환경공학회)
권호 표지
DOI QR코드

DOI QR Code

A Study on the Behaviour of Single Piles and Pile Groups in Consolidating Ground from Coupled Consolidation Analyses

연계압밀해석을 통한 압밀이 진행 중인 지반에 근입된 단독말뚝 및 군말뚝의 거동연구

  • Kim, Sung-Hee (Department of Civil Engineering, Kangwon National University) ;
  • Jeon, Young-Jin (Department of Civil Engineering, Kangwon National University) ;
  • Lee, Cheol-Ju (Department of Civil Engineering, Kangwon National University)
  • Received : 2016.03.21
  • Accepted : 2016.05.25
  • Published : 2016.07.01
Download PDF
⟨ Previous Next ⟩

Abstract

In the present work, a number of advanced three-dimensional (3D) parametric finite element numerical analyses have been conducted to study the behaviour of single piles and pile groups in consolidating ground from coupled consolidation analyses. Single piles, $4{\times}4$ and $6{\times}6$ piles inside groups with a spacing of 2.5D were considered, where D is the pile diameter. It has been found that dragload and downdrag on the piles developed rather quickly at the early stage of consolidation. However, when the degree of consolidation was more than 50~75%, only little increases of dragload and downdrag were induced on the pile. Negative Skin Friction (NSF) on the pile in the fill layer was mobilised quickly and remained constant throughout further consolidation. The development of NSF is influenced both by the relative shear displacements at the pile-soil interface and the vertical effective soil stresses during consolidation. The former governed the early stage of consolidation and the latter affected the later stage of consolidation. The vertical effective soil stresses adjacent to the piles were reduced due to the shear stress transfer at the pile-soil interface, in particular for piles inside the pile groups. The range of NSF influence zone concerning the reductions of the effective vertical soil stresses was about 20D measured from the piles in the horizontal direction. On the contrary, the effective horizontal soil stresses acting on the piles were similar to those at the far field.

본 연구에서는 압밀을 고려한 고등 3차원 유한요소해석을 통하여 압밀이 진행 중인 지반에 근입된 단독말뚝 및 군말뚝의 거동을 연구하였다. 수치해석에서는 단독말뚝 및 말뚝 중심간의 간격이 2.5D인 $4{\times}4$ 및 $6{\times}6$ 군말뚝을 고려하였다. 여기서 D는 말뚝의 직경을 의미한다. 부마찰에 의한 말뚝의 침하 및 부마찰력은 압밀초기 단계에서 비교적 빠르게 발생하는 것으로 분석되었다. 그러나 압밀도가 50~75%를 초과하는 경우 말뚝의 침하 및 부마찰력의 증가량은 상대적으로 크지 않은 것으로 분석되었다. 성토층에서의 부마찰은 신속하게 발현되며 이후의 압밀 단계에서는 일정하게 유지된다. 말뚝에 작용하는 부마찰은 상대변위 및 유효지중응력에 좌우되는 것으로 분석되었다. 압밀 초기단계에서는 상대변위가 큰 영향을 미치는데 비해, 압밀 후반기에서는 유효지중응력이 큰 영향을 주는 것으로 분석되었다. 말뚝-인접지반에서의 전단응력 전이로 인해 말뚝과 인접한 흙의 유효수직응력이 감소하며 이러한 현상은 군말뚝에서 특히 현저하다. 부마찰이 영향을 미치는 영역의 범위는 흙의 유효수직응력의 분포를 고려할 경우 말뚝으로부터 수평으로 20D 정도 되는 것으로 분석되었다. 이에 비해 말뚝에 작용하는 유효수평응력은 far field 조건의 응력과 거의 유사한 것으로 분석되었다.

Keywords

References

  1. Brinkgreve, R. B. J., Kumarswamy, S. and Swolfs, W. M. (2015), Reference manual, Plaxis 3D 2015 user's manual (Edited by Brinkgreve, R. B. J., Kumarswamy, S and Swolfs, W. M), pp. 1-284.
  2. Comodromos, E. and Bareka, S. (2005), Evaluation of negative skin friction effects in pile foundations using 3D nonlinear analysis, Computers and Geotechnics, Vol. 32, No. 3, pp. 210-221. https://doi.org/10.1016/j.compgeo.2005.01.006
  3. Jeong, S. S. (1992), Nonlinear three-dimensional analysis of downdrag on pile groups, PhD thesis, Texas A&M University, pp. 1-165.
  4. Jeong, S.S., Ko, J. Y., Lee, C. J. and Kim, J. H. (2014), Response of single piles in marine deposits to negative skin friction from long-term field monitoring, Marine Georesources & Geotechnology, 32, pp. 239-263. https://doi.org/10.1080/1064119X.2012.735344
  5. Lam, S. Y., Ng, C. W. W., Leung, C. F. and Chan, S. H. (2009), Centrifuge and numerical modelling of dragload effects on piles in consolidating ground, Canadian Geotechnical Journal, Vol. 46, No. 1, pp. 10-24. https://doi.org/10.1139/T08-095
  6. Lam, S. Y., Ng, C. W. W. and Poulos, H. G. (2013), Shielding piles from downdrag in consolidating ground, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 139, No. 6, pp. 956-968. https://doi.org/10.1061/(ASCE)GT.1943-5606.0000764
  7. Lee, C. J. (2001), The influence of negative skin friction on piles and in pile groups, PhD thesis, Cambridge University, pp. 1-R13.
  8. Lee, C. J., Bolton, M. D. and Al-Tabbaa, A. (2002), Numerical modelling of group effects on the distribution of dragloads in piles foundations, Geotechnique, Vol. 52, No. 5, pp. 325-335. https://doi.org/10.1680/geot.2002.52.5.325
  9. Lee, C. J. and Ng, C. W. W. (2004), Development of downdrag on piles and pile groups in consolidation soil, Journal of Geo-technical and Geoenvironmental Engineering, ASCE, Vol. 130, No. 9, pp. 905-914. https://doi.org/10.1061/(ASCE)1090-0241(2004)130:9(905)
  10. Lee, C. J., Lee, J. H. and Jeong, S. S. (2006), The influence of soil slip on negative skin friction in pile groups connected to cap, Geotechnique, Vol. 56, No.1, pp. 53-56. https://doi.org/10.1680/geot.2006.56.1.53
  11. Lee, C. J. (2009a), A study of the influence of negative skin friction on single piles from consolidation analyses, Journal of the Korean Geo-Environmental Society, Vol. 10, No. 2, pp. 29-36 (in Korean).
  12. Lee, C. J. (2009b), The Influence of reduction of vertical stress on the behaviour of piles subjected to negative skin friction, Journal of the Korean Society of Civil Engineers, Vol. 29, No. 1C, pp. 33-39 (in Korean).
  13. Leung, C. F., Liao, B. K., Chow, Y. K., Shen, R. F. and Kog, Y. C. (2004), Behavior of pile subject to negative skin friction and axial load, Soils & Foundations, Vol. 44, No. 6, pp. 17-26. https://doi.org/10.3208/sandf.44.6_17
  14. Leung, C. F. (2009), Negative skin friction on piles, Indian Geotechnical Conference 2009, Guntur, India, pp. 827-836.
  15. Ng, C. W. W., Poulos, H. G., Chan, V. S. H., Lam, S. S. Y. and Chan, G. C. Y. (2008), Effects of tip location and shielding on piles in consolidating ground, Journal of Geotechnical & Geoenvironmental Engineering, ASCE, Vol. 134, No. 9, pp. 1245-1260. https://doi.org/10.1061/(ASCE)1090-0241(2008)134:9(1245)
  16. Phamvan, P. (1989), Negative skin friction on driven piles in Bangkok subsoils, Ph.D Thesis, AIT, Bangkok, Thailand, pp. 1-235.
  17. Zeevaert, L. (1983), Foundation engineering for difficult subsoil conditions, 2nd Edition, Van Nostrand Reinhold Company, pp. 351-395.