Rock and Soil Mechanics ›› 2023, Vol. 44 ›› Issue (7): 1995-2004.doi: 10.16285/j.rsm.2022.6185

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Upper bound analysis of uplift piles in saturated clay and soil plug effect

ZHU Ke-wen1, 2, YU Jian1, 2, HUANG Mao-song1, 2   

  1. 1. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China 2. Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China
  • Online:2023-07-25 Published:2023-10-08
  • Contact: YU Jian, male, born in 1987, PhD, Associate Professor, mainly engaged in teaching and research work in geotechnical engineering. E-mail:
  • About author:ZHU Ke-wen, male, born in 1994, PhD candidate, focusing on geotechnical stability.
  • Supported by:
    the Natural Science Foundation of Shanghai (23ZR1468500) and the National Natural Science Foundation of China (51579177).


A new mechanism is established and applied to the upper bound analysis of uplift piles in saturated clay. Upper bound solutions of uplift capacities of closed and open-ended piles are analyzed. The new mechanism is verified by comparing with elastoplastic finite- element, existing lower bound and API solutions. Its reliability is assessed through case studies including one centrifuge test and two field tests. The effects of the pile length-diameter ratio, pile surface roughness, non-uniformity of undrained soil strength and length of soil plug on the uplift bearing capacity are considered. A formulation predicting the net bearing capacity of closed-ended uplift piles in clay is proposed. The results show that an approximately linear relationship can be established between the normalized net bearing capacity coefficient and the pile length-diameter ratio for closed-ended piles. As for open-ended pipe piles, the ratio of the net bearing capacity coefficient of open-ended pipe piles to that of closed-end piles tends to increase with the increase of the pile length-diameter ratio. The increase in the length of soil plug leads to an increase in the net bearing capacity coefficient of open-ended pipe piles. Therefore, the effect of soil plug should not be ignored.

Key words: uplift pile, limit analysis method, nonhomogeneous clay, soil plug