Adequate saturation of the High Air Entry (HAE) ceramic disc is important in order to perform a Soil Water Characteristic Curve (SWCC) test as it provides higher accuracy to the determination of the water volume changes. Saturation of the HAE disc allows a direct contact between the water in the soil pores and the water underneath the disc. In this way, water can move freely, under differential pressure, through the disc. In contrast, air cannot pass the HAE disc if it has a pressure lower than the Air Entry Value of the disc.

There are several laboratory and in situ tests that can be done to estimate the permeability of the soil and every test has its own advantages and disadvantages. The two most common are “the constant head permeability method” and “the falling head permeability method”.

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