Transmission And Substation Foundations - Technical Design Manual (TD06088E)

f s = σ o ( sin φ ) + c(cos φ )

Equation 4-42

Type III: Clays with 1024 psf < c < 4096 psf (49 kPa < c < 196 kPa)

Equation 4-43

f s = c

where: 1024 psf < c < 2048 pfs (49 kPa < c < 98 kPa) and:

Equation 4-44

f s = 2048 psf (98 kPa)

where: 2048 psf < c < 4096 psf (98 kPa < c < 196 kPa)

In HeliCAP ® this analysis assumes a uniform shaft diameter for each soil layer and, if required, the friction capacity of the pile near the surface can be omitted.

Department of the Navy Design Manual 7 Method:

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For cohesive soils (a Method):

Q f = Σ [ π (D)C a ( ∆ L f )]

Equation 4-45

where: C a = Adhesion factor (See Table 5-13)

For cohesionless soils (a Method):

Q f = Σ [ π D(qKtanf) ∆ L f ]

Equation 4-46

where: q = Effective vertical stress on element ∆ L f K = Coefficient of lateral earth pressure ranging from K o to about 1.75 depending on volume displacement, initial soil density, etc. Values close to K o are generally recommended because of long-term soil creep effects. As a default, use K o = 1. φ = Effective friction angle between soil and plate material

DESIGN METHODOLOGY

Q f = Σ [ π D(S) ∆ L f ]

Equation 4-47

where: S = Average friction resistance on pile surface area = P o tan φ (See Tables 5-5 & 5-14) P o = Average overburden pressure For straight steel pipe shaft piles in sand, HeliCAP ® uses Table 5-5 to calculate shaft resistance in sand layers using the Alternate Navy Method.

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