Axial Capacity Methods for Axially Loaded Single Piles
The following axial capacity methods are included in the PileAXL program:
​Driven Piles:
​
​(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) SPT-N Method (Clay and Sand)
(16) LCPC CPT Method (Clay and Sand)
(17) User Sand
(18) General Rock
Bored Piles or Drilled Shafts:
​
​(1) FHWA Clay
(2) Alpha Clay
(3) User Clay
(4) FHWA Sand
(6) FHWA Gravels
(8) Beta Sand
(9) SPT-N 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).
​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.
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.
User Clay - Bored Piles or Drilled Shafts
User Clay method in the PileAXL program allows the users to directly define the ultimate shaft resistance (fs) and ultimate end bearing resistance (fb).
FHWA Sand - Bored Piles or Drilled Shafts
For the cohesionless soils, the following equations as recommended in FHWA manual (O’Neill and Reese 1999) are adopted to calculate the ultimate shaft resistance, fs for sand:
where z is the depth below the ground surface, σz' is the effective overburden pressure and ɸ is the effective friction angle of the sand.
The calculation of the ultimate end bearing resistance, fb based on the effective friction angle is carried out by the following equations:
FHWA Gravelly Sand - Bored Piles or Drilled Shafts
For the cohesionless soils, the following equations as recommended in FHWA manual (O’Neill and Reese 1999) are adopted to calculate the ultimate shaft resistance, fs for gravelly sand:
where z is the depth below the ground surface, σz' is the effective overburden pressure and ɸ is the effective friction angle of the sand.
The calculation of the ultimate end bearing resistance, fb based on the effective friction angle is carried out by the following equations:
FHWA Gravel - Bored Piles or Drilled Shafts
For the cohesionless soils, the following equations as recommended in FHWA manual (O’Neill and Reese 1999) are adopted to calculate the ultimate shaft resistance, fs for gravel:
where z is the depth below the ground surface, σz' is the effective overburden pressure and ɸ is the effective friction angle of the sand.
The calculation of the ultimate end bearing resistance, fb based on the effective friction angle is carried out by the following equations:
FHWA Sand Rational Beta - Bored Piles or Drilled Shafts
For the cohesionless soils, the following equations as recommended in Chen and Kulhawy (2002) as described in FHWA-NHI-10-016 (2010) are adopted to calculate the ultimate shaft resistance, fs for granular materials:
where σz' is the effective overburden pressure, ɸ' is the effective friction angle of the sand, σp' is the effective vertical preconsolidation stress, n and m are the empirical constants for correlating SPT values with σp' as suggested by Mayne (2007) and Kulhawy and Chen (2007). The typical values are 0.47 for n and 0.8 for m.
The calculation of the ultimate end bearing resistance, fb based on the effective friction angle is carried out by the following equations:
Beta Sand - Bored Piles or Drilled Shafts
Beta Sand method uses the following equation to calculate the ultimate shaft resistance, fs for sand and gravel:
where β is the factor for shaft resistance input by the users and σz' is the effective overburden pressure.
The calculation of the ultimate end bearing resistance, fb based on the effective friction angle is carried out by the following equations:
User Sand - Bored Piles or Drilled Shafts
User Sand method in the PileAXL program allows the users to directly define the ultimate shaft resistance (fs) and ultimate end bearing resistance (fb).
Weathered Rock - Rowe and Armitage - Bored Piles or Drilled Shafts
​Weathered rock – Rowe and Armitage method for bored piles or drilled shafts calculates the ultimate shaft resistance, fs based on the following relationships:
where σc is the unconfined compressive strength (UCS) in MPa, α and β are the factors for shaft resistance. For regular clean sockets (roughness R1, R2 and R3 as defined in the table below). the shaft resistance factors are adopted as below based on Rowe and Armitage (1987):
The shaft resistance factors are adopted as below based on Rowe and Armitage (1987):
​For clean, rough (R4) sockets, the shaft resistance factors are adopted as below based on Rowe and Armitage (1987):
The ultimate end bearing resistance, fb based on Rowe and Armitage (1987) is calculated using the relationship below:
where σc is the unconfined compressive strength (UCS) in MPa and Ncr is the bearing capacity factor which is adopted as 2.5 based on Rowe and Armitage (1987).
The rock elastic mass modulus Em is calculated based on the following relationship:
