What does the Triaxial Test primarily measure?

The Triaxial Test is a critical laboratory test in geotechnical engineering that primarily measures the shear strength of soil under controlled conditions, specifically by varying drainage conditions. During the test, a cylindrical soil sample is subjected to confining pressure and axial load, allowing for the observation of the soil's behavior under both saturated and unsaturated states. This flexibility in testing is crucial because it simulates the real-world conditions that soils may experience in the field, such as differing water content and changes in pore pressure.

By understanding the shear strength of soil, engineers can make informed decisions regarding the stability of slopes, the design of foundations, and the behavior of earth structures. The Triaxial Test provides valuable data that helps predict how soil will react under shear stress scenarios, which is essential for ensuring safety and structural integrity in civil engineering projects.

The other options addressed different aspects of soil properties that are not the main focus of the Triaxial Test, such as measuring permeability, moisture content, or plasticity, which are important but serve distinct purposes in soil assessment and analysis.