Transmission And Substation Foundations - Technical Design Manual (TD06088E)

In the event that cohesion or undrained shear strength values are not available, HeliCAP ® uses the following equation to obtain estimated undrained shear strength values when blow counts from ASTM D 1586 Standard Penetration Tests are available. This equation is based on empirical values and is offered only as a guide when undrained shear strength values are otherwise not available. It is suggested that results be used with caution. (NOTE: The correlated undrained shear strength values determined by HeliCAP ® can be overridden. This is encouraged when more reliable soil data are available.) c (ksf) = N / 8 or = 0.125(N) Equation 4-35

c (kPa) = 6N where: c = “cohesion”; for φ ’ = 0; c = undrained shear strength = s u N = Blow count value per ASTM D 1586 Standard Penetration Test

Unit Weight Correlation

In the event unit weight values are not available, HeliCAP ® uses the following equations to obtain estimated unit weight values when blow counts from ASTM D 1586 Standard Penetration Tests are available.

Equation 4-36

Clay (Fine-Grain) Soils:

γ = 80 + (2N) (lb/ft 3 ) γ = 120 (lb/ft 3 )

N > 0 & N ≤ 19: N ≥ 20 & N ≤ 40

γ = 120 + 2(N-40) (lb/ft 3 )

Equation 4-37

N ≥ 41 & N < 50

γ = 140 (lb/ft 3 )

N ≥ 50

Sand (Coarse-Grain) Soils: N = 0

γ = 65 (lb/ft 3 )

γ = 60 + 5N (lb/ft 3 ) γ = 100 (lb/ft 3 )

DESIGN METHODOLOGY N > 0 & N ≤ 7

Equation 4-38

N ≥ 8 & N ≤ 10

γ = 90 + N (lb/ft 3 )

Equation 4-39

N ≥ 11 & N < 50

N ≥ 50 γ = 140 (lb/ft 3 ) These correlations were originally determined from Tables 3-2 and 3-3 in Bowles first edition of Foundation Analysis and Design . These relationships provide an approximation of the total unit weight. They have been modified slightly from how they were originally presented as experience has suggested. (NOTE: The correlated total unit weight values determined by HeliCAP ® can be overridden. This is encouraged when more reliable soil data are available.)

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