Permeability of soil can be determined by permeameters, by allowing the water to flow through soil sample under either constant head or under variable head.

Permeability measurement:

Permeability is a property of soils that determines the ease with which water can flow through them. It is an important parameter in geotechnical engineering as it influences the seepage characteristics and stability of soil structures such as foundations, embankments, and retaining walls.

Direct measurement:

Permeability can be directly measured in the laboratory using a device called a permeameter. A permeameter is a specialized apparatus designed to apply a hydraulic gradient to a soil specimen and measure the resulting flow rate of water through the specimen.

Working principle of a permeameter:

A permeameter consists of a soil sample, a flow cell, and a system for applying a hydraulic gradient. The soil sample is prepared in the form of a cylindrical specimen with a known cross-sectional area and length. The flow cell is a chamber that holds the soil specimen and allows water to flow through it. The hydraulic gradient is created by applying a pressure difference across the specimen using a water reservoir and a pressure control system.

Measurement procedure:

The permeability measurement using a permeameter involves the following steps:

1. Preparation of soil specimen: A representative soil sample is collected and compacted into the permeameter's sample chamber. The sample is carefully prepared to achieve the desired density and void ratio.

2. Saturation of the specimen: The soil specimen is fully saturated with water by allowing water to flow through it under a low hydraulic gradient. This ensures that all the void spaces are filled with water and there is no trapped air.

3. Application of hydraulic gradient: A pressure difference is applied across the specimen by connecting the flow cell to a water reservoir. The pressure control system maintains a constant pressure difference throughout the test.

4. Measurement of flow rate: The flow rate of water through the specimen is measured using a calibrated flow meter. The flow rate is typically measured at regular intervals of time to observe any variations.

5. Calculation of permeability: The permeability of the soil specimen is calculated using Darcy's law, which relates the flow rate, hydraulic gradient, and cross-sectional area of the specimen. The permeability is usually expressed in terms of centimeters per second (cm/s) or meters per second (m/s).

Advantages of direct measurement:

- Direct measurement using a permeameter provides accurate and reliable results.
- It allows for the determination of permeability under controlled laboratory conditions.
- It can be used to measure permeability of both intact and reconstituted soil specimens.
- The test can be performed on a wide range of soil types and grain sizes.

In conclusion, permeability can be determined by direct measurement using a permeameter, which applies a hydraulic gradient to a soil specimen and measures the resulting flow rate of water. This method provides accurate and reliable results, making it an essential tool for geotechnical engineers in assessing the seepage characteristics of soils.

Permeameter