How is the shear strength of soil typically measured?

The shear strength of soil is typically measured using direct shear tests or unconfined compressive strength tests. These methods provide a direct assessment of the soil's ability to resist shear stress, which is critical for understanding how the soil will behave under various loading conditions.

In a direct shear test, a soil sample is placed in a shear box and subjected to a controlled shear force that increases until the sample fails. This allows for the determination of the shear strength parameters, such as cohesion and angle of internal friction, which are essential for evaluating soil stability.

The unconfined compressive strength test is another method often used for cohesive soils. In this test, a cylindrical sample of soil is compressed until failure occurs without any lateral support. The maximum axial load at failure is measured and used to derive the unconfined compressive strength, which is related to the soil's shear strength.

The other options relate to other testing methods or properties that do not directly measure shear strength. For instance, the specific gravity test measures the density of solids in a soil sample but does not provide information about shear strength. Calculating moisture content gives insights into the water content of the soil but does not indicate how the soil will behave under shear. Observing color changes does not have