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Ultimate vertical load capacity of pile or pier

Ultimate vertical load capacity of pile or pier

Qult = Qb+ Qs – Wp =9cuAp+α cu p L

  • Qult= Ultimate vertical load capacity of pile or pier
  • Qb= Component of load capacity due to bearing capacity at pile or pier base
  • Qs= Component of load capacity due to side friction
  • α= adhesion factor
  • p=perimeter
  • L=Length

Load capacity at pile or pier base

Qb= Ab(cNc + σt‘ Nq _ 0.5 Bγb’ Nγ )

  • Where Ab= Area of pile or pier base
  • c= Soil cohesion
  • σt‘=Effective vertical stress at pile or pier base
  • B=Base diameter
  • γb’=Effective unit weight of soil in the failure zone beneath base
  • Nc, Nq, Nγ = Bearing capacity factors.

The load capacity due to skin friction on the shaft of the pile

Qs= ∑ σt‘ Khc tanδPL

  • Where, σt‘= Effective overburden pressure
  • Khc = Ratio of horizontal to vertical pressure–pile in compression
  • δ = friction angle between pile and soil
  • P= Perimeter or circumference of pile, For circular pile, P=∏D
  • L= length of the pile.

Carrying Capacity of a Single Pile or Pier in Granular Soil

Qult= Ab σt‘ Nq +∑ σt‘ Khc tanδPL, Where, c=0, Nγ =0

Carrying Capacity of a Single Pile or Pier in Cohesive Soil

Qb-ult= Abc Nc Where, c=.5qu, Nq =0 and δ=0

Skin Friction factor for Driven Piles

Qs-ult =∑ α cu PL

Settlement of Pile Groups

Granular Soil

Sg= Si√(B / D )

  • where Sg= Settlement of pile group
  • Si =Settlement of a single pile estimated or determined from load tests
  • B= Smallest dimension of pile group
  • D= Diameter of individual pile.

Displacement

δe= PL /AE

  • Where, δe = Elastic compression
  • P= Axial load on pile
  • L = Pile length (for end-bearing pile)
  • A= Cross-sectional area of pile material
  • E = Modulus of elasticity of pile material

Displacement

Sf= δe +(0.15+D/120) (where, Sf= Displacement at failure in inches, δe= Elastic compression, D= Pile diameter in inches)

PILE CAPACITY FROM DRIVING DATA

Danish Formula

Qdy = αWHH/(S+0.5Se), Se=√(2αWHHL/AE)

  • Qdy= Ultimate dynamic bearing capacity of driven pile
  • α=Pile driving hammer efficiency (normally 1)
  • WH= Weight of hammer
  • H= Hammer drop (note that WH H= Hammer energy)
  • S= Inelastic set of pile, in distance per hammer blow
  • Se= Elastic set of pile, in distance per hammer blow
  • L = Pile length
  • A= Pile end area
  • E= Modulus of elasticity of pile material

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