The correct answer is A. constant head method.
The constant head method is the most suitable method for the determination of permeability of clayey soil because it is the most accurate and reliable method. The falling head method is not as accurate as the constant head method because it is affected by the surface tension of the water. The horizontal permeability test is not suitable for clayey soil because clayey soil is not a homogeneous material.
The constant head method is a laboratory test used to determine the permeability of soil. The test is conducted by placing a sample of soil in a permeameter and applying a constant head of water to the top of the sample. The rate at which water flows through the sample is measured, and the permeability of the soil is calculated from this data.
The falling head method is a laboratory test used to determine the permeability of soil. The test is conducted by placing a sample of soil in a permeameter and allowing water to flow through the sample under a falling head of water. The rate at which water flows through the sample is measured, and the permeability of the soil is calculated from this data.
The horizontal permeability test is a field test used to determine the permeability of soil. The test is conducted by excavating a trench in the soil and filling it with water. The rate at which water flows through the trench is measured, and the permeability of the soil is calculated from this data.
Clayey soil is a type of soil that is composed of very fine particles of clay. Clayey soil is very dense and has a low permeability. This means that water flows very slowly through clayey soil.