Which method is commonly used to estimate soil permeability?

The constant head test is commonly used to estimate soil permeability because it is specifically designed to measure the rate at which water flows through soil under a constant hydraulic head. This method is particularly suitable for granular soils, such as sands and gravels, which have relatively high permeability.

In the constant head test, water is allowed to flow through a soil sample at a steady rate, and the volume of water collected over a specific period is measured. The test operates under the assumption that the soil is saturated and the flow is laminar, which allows for a calculation of the hydraulic conductivity or permeability of the soil. This quantifies how easily water can move through the soil, making it a key parameter for various geotechnical engineering applications, including drainage design and groundwater flow analysis.

Other methods mentioned do not serve the purpose of measuring permeability. The Atterberg limits test assesses the plasticity characteristics of fine-grained soils, the Proctor compaction test evaluates moisture-density relationships for optimal compaction of soil, and the plasticity index test provides insights into the range of moisture content over which soil remains plastic. While these tests are valuable in soil characterization, they do not directly measure the permeability of the soil.