Which test determines permeability by measuring changes in head level over time?

The Falling Head Test is specifically designed to determine the permeability of soil by measuring changes in water level (head) over time. In this method, a soil sample is placed in a permeameter and water is allowed to flow through it, while the head level is monitored. As water drains through the soil, the decrease in water level is measured at timed intervals. This change in head level is then used to calculate the hydraulic conductivity, indicating how easily water can flow through the soil.

This test is particularly useful in fine-grained soils where the permeability is lower, as it allows for an accurate assessment in conditions where a constant flow rate may not be easily maintained, as would be the case in constant head tests. The falling head setup takes into account the changing water level, which provides a clear picture of the soil’s permeability characteristics over time.