Permeability is a property of soil that indicates its ability to allow water to pass through it. It is an important concept in Geotechnical Engineering. Definition Permeability is defined as the ease with which water flows through soil under a hydraulic gradient. Coefficient of Permeability (k) It is the rate of flow of water through a unit cross-sectional area of soil under a unit hydraulic gradient. Types of Permeability Tests Constant head test (for coarse soils) Falling head test (for fine soils) Applications of Permeability Design of earth dams and embankments Seepage analysis in soil structures Design of drainage systems Stability analysis of slopes Design of foundations Groundwater flow studies Design of filters and retaining structures Irrigation and canal design