Document Type : Research Paper


Civil Engineering Dept., University of Technology-Iraq, Alsina’a street, 10066 Baghdad, Iraq.


A 3D numerical model generated using PLAXIS-3D software was used in the present research to predict the behavior of under-reamed piles under pullout loading conditions with presumed soil Mohr-Coulomb failure. The under-reamed pile was embedded in homogeneous, layered clay soil, with stiff clay overlain by soft clay and soft clay overlain by stiff clay. The piles were chosen per the Indian Code (IS 2911) specification, and two variables were studied: bulb provision and soil layering. Inhomogeneous clay with varying cohesion values (20, 40, and 80 kPa) and under the same conditions, the pullout capacity was improved compared to a straight shaft (SP). The pullout capacity of the single bulb (SURP) increased once, while that of the double bulb (DURP) increased twice. The results revealed that anchoring the pile in a stronger stratum at a greater depth is advantageous when designing under-reamed pile foundations. In the case of stiff clay on top of soft clay, additional resistance against pullout is achieved, reducing the risk of pullout failure compared to soft clay in the upper layer.

Graphical Abstract


  • Increased soil cohesiveness improves the load-deformation behaviour of the under-reamed pile under pullout loads.
  • The bearing pullout load rises as the number of bulbs increases.
  • The maximum ultimate pullout capacity is obtained in the case of the stiff clay resting on the soft clay.
  • The failure patterns of soil movement around the projections were larger than those around the shaft.


Main Subjects

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