Coefficient of permeability or simple permeability is expressed in terms of cm/sec, m/day, and feet/day.

The coefficient of permeability is a measure of the ability of a porous medium, such as soil or rock, to allow the flow of fluids through it. It is an important parameter in geotechnical engineering and hydrogeology, as it governs the movement of groundwater and other fluids through the ground.

The coefficient of permeability is defined as the rate of flow of a fluid through a unit area of the porous medium under a unit hydraulic gradient. It is denoted by the symbol "k" and has dimensions of length per time.

The coefficient of permeability can be expressed in various units, depending on the system of measurement used. The most common units are:

1. cm/sec: This unit is commonly used in the metric system. It represents the rate of flow of a fluid through a unit area of the porous medium in centimeters per second. This unit is convenient for laboratory testing and small-scale applications.

2. m/day: This unit is also commonly used in the metric system. It represents the rate of flow of a fluid through a unit area of the porous medium in meters per day. This unit is often used in field measurements and large-scale applications.

3. feet/day: This unit is commonly used in the Imperial system of measurement. It represents the rate of flow of a fluid through a unit area of the porous medium in feet per day. This unit is still used in some regions where the Imperial system is prevalent.

Since the coefficient of permeability can be expressed in different units, it is important to convert between these units when necessary to ensure consistency in calculations and comparisons.

In summary, the coefficient of permeability or simple permeability is expressed in terms of cm/sec, m/day, and feet/day, depending on the system of measurement used. The choice of unit depends on the specific application and the preferences of the engineer or scientist conducting the analysis.