The axial compression of a pile is given by the equation

Dp = ((Qb + "sQs)L + (Qb + Qs)(Lt-L))/(AbEp)............(1)

where

Dp

=

settlement from axial deformation of the

shaft, m or ft

Qb =

design load at the pile toe, kN or kips

"s =

distribution factor for load along the pile

length = 0.5 to 0.67; normally assume 0.5

Qs =

design load taken by shaft friction, kN or

kips

L

=

embedded length, m or ft = 16.159m or 53 ft

Lt

=

total pile length = 25.9m (85')

Ab

=

toe bearing area, m2 or ft2 = .258 m2 or

2.78 ft2

Ep

=

pile modulus of elasticity = 20,682,000 kPa

(432,000 kips/ft2)

A rough estimate of Qs may be made by assuming that Qs = Qsu, since nearly all

shaft resistance will be mobilized before significant toe resistance, unless the

pile toe is bearing on a hard stratum. Qb is then estimated by subtracting Qsu

from the design load Qd. If Qb and Qs are each assumed to take half of the load

or 267 kN (60 kips), then

Dp = 0.00218m (0.0072')...........(2a -- Qb = Qs = 267 kN)

If the design load of 534 kN (120 kips) is assumed to be taken totally by shaft

Dp = 0.00178m (.0058').................(2b -- Qs = 534 kN)

Figure 5-10. Computation of axial pile compression.

5-16

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