What laboratory test is used to determine the Unconfined Compressive Strength (UCS)?

The laboratory test specifically designed to determine the Unconfined Compressive Strength (UCS) of a soil sample is the Unconfined Compressive Strength test. This test measures the maximum axial compressive stress that a cylindrical sample of soil can withstand under unconfined conditions, meaning that the sample is not subjected to any lateral pressure.

In this test, a cylindrical specimen is loaded axially until failure occurs, allowing for a direct measurement of compressive strength. The result is essential in evaluating the strength properties of cohesive soils, which is critical for engineering and construction applications. The UCS value obtained is an indicator of soil solidity and stability under load.

The other options represent different types of tests that serve various purposes but do not specifically measure UCS. For example, the triaxial test assesses soil strength under controlled conditions of cell pressure and deviator stress, while the direct shear test evaluates the shear strength parameters of soils. The compaction test, on the other hand, focuses on determining the optimum moisture content and maximum dry density of soil but does not provide a direct measurement of compressive strength.