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API Sand

The American Petroleum Institute (2002) defines the strength for a driven pile in sand as follows:

  • Friction Angle - A parameter to quantify the shear strength of soil. For API Sand, a cohesionless soil, the effective shear strength of soil (Effective Shear Strength of Soil Symbol) is calculated as Effective Shear Strength of Soil Equation where the effective normal stress (Effective Normal Stress Symbol) is multiplied by the tangent of the friction angle (Friction Angle Symbol).
  • Coefficient of Lateral Earth Pressure - The ratio of the horizontal to the vertical stress
  • Bearing Capacity Factor - A multiplication factor to characterize the bearing resistance (q) as a ratio of the overburden pressure (), Bearing Resistance Equation, where Nq = Bearing Capacity Factor. Refer to the theory manual for more information.
  • Maximum Unit Skin Friction - The maximum allowable unit skin friction that can be computed in the soil layer. The restriction is to prevent an overestimate of the skin friction, especially for thick soil layers.
  • Maximum Unit End Bearing Resistance - The maximum allowable unit end bearing resistance that can be computed in the soil layer. The restriction is to prevent an overestimate of the end bearing resistance, especially for thick soil layers.

API Sand Skin Friction (t-z) Load Transfer Curve

API Sand Skin Friction (t-z) Load Transfer Curve

API Sand and Clay End Bearing (Q-z) Load Transfer Curve

API Sand and Clay End Bearing (Q-z) Load Transfer Curve

DESIGN PARAMETERS FOR COHESIONLESS SILICEOUS SOILS* (API 2002)

API (2002) provides some recommendations on the soil properties of cohesionless soils.

Density

Soil Description

Soil-Pile Friction Angle

Max Skin Friction Values
kPa (kips/ft2)

Bearing Capacity Factor, Nq

Max Unit End Bearing Values
MPa (kips/ft2)

Very Loose
Loose
Medium

Sand
Sand-Silt**
Silt

15

47.8 (1.0)

8

1.9(40)

Loose
Medium
Dense

Sand
Sand-Silt**
Silt

20

67.0(1.4)

12

2.9(60)

Medium
Dense

Sand
Sand-Silt**

25

81.3(1.7)

20

4.8(100)

Dense
Very Dense

Sand
Sand-Silt**

30

95.7(2.0)

40

9.6(200)

Dense
Very Dense

Gravel
Sand

35

114.8(2.4)

50

12(250)

*The parameters listed in this table are intended as guidelines only. Where detailed information such as in situ cone tests, strength tests on high-quality samples, model tests, or pile driving performance is available, other values may be justified.

**Sand-Silt includes those soils with significant fractions of both sand and silt. Strength values generally increase with increasing sand fractions and decrease with increasing silt fractions.

For more information, see the Axial Analysis Theory Manual.

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