What laboratory testing method is used to determine the permeability of fine-grained soils such as silts and clays?

The Falling Head Permeability Test is specifically designed for determining the permeability of fine-grained soils, including silts and clays. This test is suitable for materials with low permeabilities, which are characteristic of fine-grained soils. The setup involves allowing water to flow through a soil sample while the head of water decreases over time. By measuring the time it takes for the water level in a standpipe to fall to a specific level, the flow rate can be calculated. The falling head approach is ideal for fine-grained soils because these types of soils have slow permeability, making it more appropriate than other methods such as the constant head test, which is more effective for coarse-grained soils with higher permeability.

In contrast, the Constant Head Permeability Test is not suitable for fine-grained soils because it requires a higher hydraulic gradient that may simply not be achievable in these types of soils. The Soil Compaction Test assesses the density and moisture content of soils but does not evaluate permeability. The Atterberg Limits Test, which determines the plasticity and consistency of soils, is unrelated to permeability measurements. Thus, the Falling Head Permeability Test is the appropriate method for this context.