Axial Capacity Methods for Axially Loaded Single Piles
The following axial capacity methods are included in the PileAXL program:
â€‹Driven Piles:
â€‹
â€‹(1) API Clay
(2) API COMM Clay
(3) USACE Clay
(4) ICP Clay
(5) NGI Clay
(6) UWA Clay
(7) Alpha Clay
(8) User Clay
(9) API Sand
(10) API RP2GEO Sand
(11) ICP Sand
(12) Furgo Sand
(13) UWA Sand
(14) NGI Sand
(15) SPTN Method (Clay and Sand)
(16) LCPC CPT Method (Clay and Sand)
(17) User Sand
(18) General Rock
Bored Piles or Drilled Shafts:
â€‹
â€‹(1) FHWA Clay
(2) Alpha Clay
(3) User Clay
(4) FHWA Sand
(5) FHWA Gravelly Sand
(6) FHWA Gravels
(7) FHWA Sand Rational Beta
(8) Beta Sand
(9) SPTN Method (Clay and Sand)
(10) UWA CPT Method (Clay and Sand)
(11) LCPC CPT Method (Clay and Sand)
(12) User Sand
(13) Weathered Rock  Rowe and Armitage
(14) Weathered Rock  Williams and Pells
(15) Weathered Rock  Zhang and Einstein
(16) Weathered Rock  Pells et al
(17) Weathered Rock  Kulhawy and Phoon
(18) Weathered Rock  General
(19) Weathered Rock  User Rock
FHWA Clay  Bored Piles or Drilled Shafts
FHWA Clay method for bored piles or drilled shafts is based on the approach recommended in FHWA manual (O’Neill and Reese 1999). The following equations are adopted in the PileAXL program to calculate the ultimate shaft resistance, fs and ultimate end bearing resistance, fb:
where su is undrained shear strength and pa is the atmospheric pressure (100 kPa).
â€‹where L is pile length and D is the pile diameter. Note that fb cannot be greater than 3800 kPa for bored piles within the cohesive soils according to O’Neill and Reese (1999) and Nc cannot be greater than 9.0.
The parameter input dialog for FHWA Clay method is shown on the left. The required input parameters for this method are summarized as below:

Total unit weight, ϒ (kN/m^3 or lbf/ft^3).

Undrained shear strength, Su (kPa or lbf/ft^2). This is the undrained shear strength at the layer top.

Su – Rate of Change (kPa/m or lbf/ft^3). This is the rate of change for undrained shear strength along the depth below the layer top.
Alpha Clay  Bored Piles or Drilled Shafts
Alpha Clay method available in the PileAXL program calculates the ultimate shaft resistance (fs) and ultimate end bearing resistance (fb) based on the following equations:
where su is undrained shear strength and α is the adhesion factor which can be defined by the users.
The parameter input dialog for FHWA Clay method is shown on the left. The required input parameters for this method are summarized as below:

Total unit weight, ϒ (kN/m^3 or lbf/ft^3).

Undrained shear strength, su (kPa or lbf/ft^2). This is the undrained shear strength at the layer top.

su – Rate of Change (kPa/m or lbf/ft^3). This is the rate of change for undrained shear strength along the depth below the layer top.

Nq  Bearing capacity factor.
Alpha Clay  Bored Piles or Drilled Shafts
Alpha Clay method available in the PileAXL program calculates the ultimate shaft resistance (fs) and ultimate end bearing resistance (fb) based on the following equations:
where su is undrained shear strength and α is the adhesion factor which can be defined by the users.
The parameter input dialog for FHWA Clay method is shown on the left. The required input parameters for this method are summarized as below:

Total unit weight, ϒ (kN/m^3 or lbf/ft^3).

Undrained shear strength, su (kPa or lbf/ft^2). This is the undrained shear strength at the layer top.

su – Rate of Change (kPa/m or lbf/ft^3). This is the rate of change for undrained shear strength along the depth below the layer top.

Nq  Bearing capacity factor.