Which method is used to determine the permeability of granular soils like sands and gravels?

The method used to determine the permeability of granular soils, such as sands and gravels, is the Constant Head Permeability Test. This test is particularly suitable for coarse-grained soils that allow water to flow freely through their voids without significant resistance. In this test, water is supplied from a constant head reservoir, and the flow rate is measured to calculate the permeability coefficient.

The Constant Head method is effective for obtaining accurate permeability values because it maintains a consistent pressure head throughout the test, ensuring that the flow of water through the soil sample is steady and abundant. This allows for a clear measurement of the hydraulic conductivity, which is essential for understanding water movement in soil and its implications for engineering projects.

While the Falling Head Permeability Test is also a valid method used to determine permeability, especially for fine-grained soils where flow rates are lower, it does not provide the same reliability for granular soils like sands and gravels. Additionally, other options like the Permeability Coefficient Test and Shear Strength Test do not specifically address the measurement of permeability, making them unsuitable choices for this question.