# Understanding Geotechnical Testing: Unconfined and Triaxial Tests

## Key Questions:

a) What is the unconfined compression strength of the clay sample based on the test results?

b) How is the shear strength of the tested sample in the unconsolidated-undrained triaxial test calculated?

c) Can the area ratio of the SPT sampler be determined from the given information?

d) What is the SPT value for the provided blow counts of 6, 10, and 15?

e) How can the N60 value be determined considering the hammer efficiency and blow counts?

## Answers:

a) The unconfined compression strength of the clay sample is 3500 psf.

b) The shear strength of the tested sample in the unconsolidated-undrained triaxial test is 3000 psf.

c) The area ratio of the SPT sampler cannot be determined with the given information.

d) The SPT value for the given blow counts of 6, 10, and 15 cannot be determined without additional information.

e) The N60 value cannot be calculated without the total number of blows and the energy ratio of the hammer used.

## Understanding Geotechnical Testing

Geotechnical testing plays a crucial role in determining the properties of soil and rock materials for various engineering projects. Two common tests used in geotechnical investigations are the unconfined and triaxial tests.

## Unconfined Test:

In an unconfined test, the clay sample is subjected to axial compression without lateral confinement. The major stress at failure of 3500 psf represents the unconfined compression strength of the clay sample, indicating its ability to withstand compression forces.

## Triaxial Test:

In the unconsolidated-undrained triaxial test, both major and minor principal stresses at failure are known. The shear strength of the tested sample is calculated by finding the difference between the major and minor principal stresses. In this case, the shear strength is determined to be 3000 psf based on the given stress values.

## Standard Penetration Test (SPT):

The Standard Penetration Test (SPT) is a widely used in situ test for determining the soil's resistance to penetration. The SPT value is calculated by summing the blow counts per foot of penetration during the test. However, additional information such as the total number of blows and the energy ratio of the hammer used is needed to accurately determine the SPT value and the N60 value.

## Conclusion:

Geotechnical testing provides valuable insights into the mechanical properties of soil and rock materials, helping engineers make informed decisions during the design and construction phases of projects.