Question

A) Unconfined test was ran on a clay smaple and the major stress at failure is 3500psf. What is the unconfined compression strength of the clay sample?

b) Unconsolidated-undrained triaxial test was ran on a clay sample with the major principal stress of 3500psf and the minor principle stress at failure was 500psf. What is the shear strength of the tested sample?
c) What is the area ratio of the SPT sampler?
d) A SPT sampler was driven into soil and the blow counts were reported as 6, 10, 15. What is the SPT value?
e) If the hammer efficiency is 85% for the hammer that was used in taking the SPT sample in the above question. What is the N60 value?

Answer 1

a) Unconfined Compression Strength:

The unconfined compression strength of a clay sample is the maximum stress that the sample can withstand without any lateral confinement.

Given:

Major stress at failure (σ1) = 3500 psf

The unconfined compression strength is equal to the major stress at failure.

Unconfined Compression Strength = Major stress at failure

Unconfined Compression Strength = 3500 psf

b) Shear Strength:

The shear strength of a clay sample can be determined from the major and minor principal stresses at failure in a unconsolidated-undrained triaxial test.

Given:

Major principal stress at failure (σ1) = 3500 psf

Minor principal stress at failure (σ3) = 500 psf

The shear strength (τ) is given by the difference between the major and minor principal stresses at failure.

Shear Strength = Major principal stress at failure - Minor principal stress at failure

Shear Strength = 3500 psf - 500 psf

Shear Strength = 3000 psf

c) Area Ratio of SPT Sampler:

The area ratio of a Standard Penetration Test (SPT) sampler is the ratio of the cross-sectional area of the sampler to the cross-sectional area of the drill rod.

The area ratio is typically provided by the manufacturer and may vary depending on the type and size of the SPT sampler being used. Please refer to the specifications provided by the manufacturer or consult relevant engineering standards for accurate information.

d) SPT Value:

The Standard Penetration Test (SPT) value is a measure of the resistance of soil to penetration by a standard sampler driven by a standard hammer.

Given:

Blow counts = 6, 10, 15

The SPT value is the sum of the blow counts for the first 12 inches of penetration, also known as the "N value".

SPT Value = Sum of blow counts for first 12 inches

SPT Value = 6 + 10 + 15

SPT Value = 31

e) N60 Value:

The N60 value is an adjusted SPT value that represents the number of blows required for standard penetration of a soil sample over a 12-inch length after correction for hammer efficiency.

Given:

Hammer efficiency = 85%

SPT Value = 31

The N60 value can be calculated by multiplying the SPT value by the hammer efficiency and rounding it to the nearest integer.

N60 Value = SPT Value * Hammer efficiency

N60 Value = 31 * 85%

N60 Value ≈ 26 (rounded to nearest integer)

Step-by-step explanation: