Shear strength in soils can be measured by which of the following tests?

Shear strength in soils is a critical parameter in geotechnical engineering, as it influences the stability of structures and slopes. The correct answer encompasses several testing methods specifically designed to assess the shear strength of soil samples.

The vane shear test measures the torque required to rotate a device inserted into the soil, which provides an indication of the soil's undrained shear strength, especially in soft clays. The direct shear test involves applying a shear force to a soil specimen until failure occurs, allowing for the determination of both the shear strength and the corresponding normal stress at failure. The triaxial test, another essential method, evaluates soil strength under controlled drainage conditions and varying confining pressures, providing comprehensive insights into the soil's behavior under different loading scenarios.

In contrast, the Standard Proctor Test primarily assesses the optimum moisture content and maximum dry density of soils and does not directly measure shear strength. The California Bearing Ratio (CBR) test focuses on measuring the strength of subgrade soil and pavement materials but does not assess shear strength in the way that the tests mentioned in the correct answer do. Lastly, the permeability test determines the rate at which water can flow through soil, reflecting soil drainage properties rather than shear strength.

Thus, the correct tests for