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An Analytical Model to Study the Behavior of Non-connected Piled Rafts with Granular Cushion Subjected to Vertical Load

Abstract

Understanding the load transfer mechanism and the load settlement behavior of non-connected piled raft foundations with cushion is so complicated. In the present research, based on the assumption of an axisymmetric cylindrical unit cell including pile, subsoil, cushion, and raft, an analytical model is developed and introduced. This model is capable of estimating the transferred vertical stress from raft to piles head and subsoil, compression of cushion, and differential settlement between pile head and subsoil. Also, an experimental test program has been introduced to investigate the behavior of non-connected piled raft foundations and to validate the proposed model. To represent the effectiveness of using non-connected piled raft with different cushion thickness, number, and length of piles measure with the unpiled raft, the load improvement ratio and the settlement efficiency ratio are used. According to the results, the minimum increase in the bearing capacity and the reduction in the settlement of non-connected piled raft to the unpiled raft are 42% and 38% respectively. Also, increasing the cushion thickness increases the differential settlement at the pile head elevation, and for a given number and length of pile, reduced the bearing capacity of the piled raft by 30%. The good agreement of model predictions with the experimental results is verified. The difference between the experimental and analytical values of the cushion compression above the pile head is within an acceptable range.

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Acknowledgements

The authors are grateful to Dr. Ahmad Aftabi Sani of the Ferdowsi University of Mashhad for his favor, kindness, and precious guidance. The performed tests were financially supported by the “Vice President for Research and Technology” of the Ferdowsi University of Mashhad which is acknowledged.

Funding

All the Ph.D. research programs in Ferdowsi University of Mashhad are supported by the “Vice President for Research and Technology” of the Ferdowsi University of Mashhad.

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Correspondence to Jafar Bolouri Bazaz.

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Malekkhani, M.J., Bazaz, J.B. An Analytical Model to Study the Behavior of Non-connected Piled Rafts with Granular Cushion Subjected to Vertical Load. Int J Civ Eng 19, 941–956 (2021). https://doi.org/10.1007/s40999-021-00611-1

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Keywords

  • Non-connected piled raft
  • Analytical analysis
  • Cushion
  • Negative friction
  • Pile settlement