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Bearing capacity of pile groups under vertical eccentric load

  • Raffaele Di Laora
  • Luca de Sanctis
  • Stefano Aversa
Research Paper
First Online:
Received:
Accepted:
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Abstract

The paper deals with the problem of the bearing capacity of pile groups under vertical eccentric load. Widespread practice is to consider the achievement of the axial capacity on the outermost pile as the ultimate limit state of the pile group. However, this approach neglects the ductility of the foundation system and may be thereby overconservative. With the aim of proposing an alternative and more rational approach, a novel formulation for interaction diagrams based on theorems of limit analysis is presented and discussed. The methodology is applicable to the general case of groups of unevenly distributed, dissimilar piles. Piles’ connections to the pile cap are modeled as either hinges or rigid-plastic internal fixities. An application example to a slender structure is also provided, showing that the proposed approach can lead to significant advantages over the traditional design.

Keywords

Bearing capacity Eccentric loading Limit analysis Pile groups 

List of symbols

α

Adhesion factor

αM

Inclination of the applied moment vector

γb,γs

Partial resistance factors for pile base and shaft capacity

γst

Partial factor for shaft capacity in tension

γsu

Partial factor for undrained shear strength

δ

Coefficient depending on number of piles

δθ

Increment of rotation

δWi,δWk

Increments of work done by internal forces

δEi,δEk

Increments of work done by external forces

η

Efficiency of a pile group

ξ3

Correlation factor to derive characteristic value

ξj

Coordinate of the j-th pile in the reference system (ξ, η)

σVL

Total overburden stress at depth L

Ab

Base area of the block containing the piles

As

Side area of the block containing the piles

B

Distance between two external piles of a row

c

Abscissa of the center of the row

d

Pile diameter

L

Pile length

M

External moment vector

M0

Moment capacity of the pile group under zero axial loading

Mu,Mui, Muk

Moment capacities of the pile group

Mux,Muy

Moment capacities along x- and y-axes in the 3D domain

m

Number of alignments of piles parallel to external moment vector M

myc,myt

Dimensionless yielding bending moments

Myc,Myt

Yielding bending moments

Nc

Bearing capacity factor

Nu

Axial capacity of the single pile in compression

Nuj

Axial capacity in compression of the j-th pile

n

Number of piles in a row

p

Number of piles in a group

pk

Unit base resistance

Pk

Characteristic value of pile base resistance

Q

External axial capacity

Qi,Qj

Axial loads on piles i an j

Q0

Axial capacity of the pile group

Qu,Qui, Quk

Axial capacity of the pile group

Sk

Characteristic value of pile shaft resistance

Su

Axial capacity of the single pile in uplift

Suj

Axial capacity in uplift of the j-th pile

s

Pile spacing

sk

Unit shaft resistance

su

Soil undrained shear strength

xj

Abscissa of the j-th pile

yj

Ordinate of the j-th pile

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Notes

Acknowledgements

This research has been developed under the auspices of research projects ReLUIS 2014-2017, granted by Italian Emergency Management Agency.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Università della Campania “Luigi Vanvitelli”AversaItaly
  2. 2.Università di Napoli ParthenopeNapoliItaly

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