Pile Axial Deformation

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Pile Axial Deformation Pile Group

• Prof. Jie Han, Ph.D., PE
• The University of Kansas

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Outline of Presentation

• Introduction
• Deformation under Axial Loads
• Pile Group Effects

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Deformation under Axial Loads
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Soil Modulus Profile
Soil modulus, E
E0modulus at z0
Emmodulus at mid-depth
Pile
z0.5L
EL modulus at toe
zL
Etmodulus below toe
z
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Axial Load-Displacement Prediction
Displacement of axially loaded pile (Randolph and
Wroth, 1978)
P axial load at the top of the pile I?
influence factor EL modulus at the toe d
diameter of the pile
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Influence Factor
L pile length ? dt/d, dt - diameter of pile
tip ? EL/Et ? Em/EL ? 2(1?s)Ep/EL ?
ln??0.25(2.5?(1-?s)-0.25)??(2L/d)?
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Pile Group Effects
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Typical Pile Group Patterns- Isolated Pile Caps
3 piles
4 piles
5 piles
6 piles
7 piles
8 piles
9 piles
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Typical Pile Group Patterns- Foundation Walls
Single row
Double row
Triple row
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Pile Group Effect
Stress influence
Interaction
Interaction
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Minimum Center-to-Center Pile Spacing
Pile type
Friction
End bearing
BOCA, 1993
2d or 1.75h gt 760mm
2d or 1.75h gt 610mm
NBC, 1976
2d or 1.75h gt 760mm
2d or 1.75h gt 610mm
Chicago, 1994
2d or 2h gt 760mm
d pile diameter h diagonal of rectangular
shape or H pile
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Pile Group Efficiency
AASHTO (1990) recommended the Converse- Labarre
Formula (Bolin, 1941)
(n-1)m (m-1)n
? 1 - ?
90mn

• m number of rows of piles
• n number of piles per row
• tan-1(d/s) (expressed in degrees)
• s center-to-center spacing of piles

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Pile Group Efficiency
Pg
?
nPs
Pg load capacity of piles in group N number
of piles in group Ps load capacity of a single
pile
For most cases in clay
? lt 1.0
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Pile Group Load Capacity
Lg
D
su1
Bg
su2
Pg 2D(Bg Lg)su1 BgLgsu2Nc
Nc 5(1 D/(5Bg))(1Bg/(5Lg)) lt 9
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Settlement
Pg
zi
D
Bg
30o
zf
zi 0.67D
For friction piles
For end-bearing piles
zi D