Transmission And Substation Foundations - Technical Design Manual (TD06088E)

φ ’ from SPT Several correlations have been proposed to estimate the drained friction angle in sands from SPT results. A summary of several of the more popular correlations are given in Table 4-11. The correlation of Hatanaka & Uchida (1996) is shown in Figure 4-10, taken from FHWA Reference Manual on Subsurface Investigations (2002). TABLE 4-9. TERMS TO DESCRIBE CONSISTENCY OF SATURATED COHESIVE SOILS Consistency Term Stress History SPT N 60 - Values Undrained Shear Strength skf (kPa) Comments

Normally Consolidated OCR = 1 Normally Consolidated OCR @ 1 – 1.2 Normally Consolidated OCR = 1 to 2 Normally Consolidated to OCR of 2-3.

Very Soft

0 - 2

<0.25 (12)

Runs through fingers.

Soft

3 - 5

0.38 (18.2) to 0.63 (30.2)

Squeezes easily in fingers.

Medium

6 - 9

0.75 (36) to 1.13 (54.1)

Can be formed into a ball.

Hard to deform by hand squeezing.

Stiff

10 - 16

1.25 (59.9) to 2 (95.8)

DESIGN METHODOLOGY

Overconsolidated OCR = 4 – 8

Very Stiff

17 - 30

2.13 (102) to 3.75 (179.6)

Very hard to deform by hand.

Highly Overconsolidated OCR > 8

Nearly impossible to deform by hand.

Hard

>30

>3.75 (179.6)

φ’fromCPT/CPTU A similar approach may be used to estimate the friction angle of sands from the CPT/CPTU tip resistance based on a modified bearing capacity theory. Robertson and Campanella (1983) summarized a number of available calibration chamber tests on five sands and suggested a simple correlation between the normalized CPT tip resistance and a cone bearing capacity factor, N q as: N q = (q c /s v0 ’) = 0.194exp(7.63tan φ ’) Equation 4-26 where: σ v0 ’ = vertical effective (corrected for pore water pressure) stress at cone tip This relationship is shown in Figure 4-14. The friction angle may also be estimated from the effective tip resistance from the CPTU. Early calibration chamber data suggested a simple empirical correlation as:

Equation 4-27

φ ’ = arctan[0.1 + 0.38 log (q t / σ ’ vo )]

Equation 4-27 is shown in Figure 4-16.

Page 4-27 | Hubbell Power Systems, Inc. | All Rights Reserved | Copyright © 2017