Which one of the following conditions is valid in case of unconfined c...
Unconfined compression test is a special case of tri-axial test in which the confining pressure is zero. This test may be conducted on undisturbed or remoulded cohesive soils. It cannot be conducted on coarse-grained soils such as sands and gravels as these cannot stand without lateral support.
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Which one of the following conditions is valid in case of unconfined c...
Unconfined Compression Test vs Tri-axial Test
Unconfined Compression Test and Tri-axial Test are two methods of testing the strength of soil. The following conditions are valid in case of unconfined compression test in comparison to tri-axial test:
Minor Principal Stress = 0
In the unconfined compression test, the soil sample is loaded axially without any lateral confinement. This means that there is no minor principal stress acting on the soil sample during the test. On the other hand, in the tri-axial test, the soil sample is loaded axially while being confined laterally by a rubber membrane. This results in the development of a minor principal stress in the soil sample.
Therefore, the correct answer is option 'A' - Minor principal stress = 0.
Other Conditions
The other conditions in the two tests are as follows:
- Major Principal Stress: The major principal stress is the same in both tests as it is the axial load applied to the soil sample.
- Shear Stress: In the unconfined compression test, the shear stress is developed due to the axial load applied to the soil sample. In the tri-axial test, the shear stress is developed due to both the axial load and the lateral confinement.
- Strain: The strain in the soil sample is measured in both tests using strain gauges or extensometers. However, the type of strain measured may be different in the two tests.
Conclusion
In conclusion, the major difference between unconfined compression test and tri-axial test is the presence or absence of lateral confinement. This results in the development or absence of minor principal stress in the soil sample.