Dynamic Measurement of Air Permeability as a Function of Water Content

Determining the air permeability of a soil column as a function of water content is typically a tedious task because each measurement of permeability requires a constant water content over space and time. Between each individual measurement of permeability, the water content of the sample must be modified and allowed to equilibrate. A dynamic air permeability test is proposed that measures airflow rate, water content, and air pressure, while continually modifying the water content. Dry air is pumped into the inlet of an initially wet soil column, which slowly dries the soil within approximately 24-48 hours. A computer controlled gamma ray attenuation system measures and logs the water content along the length of the soil column over time. Hypodermic needles are inserted into the soil column and connected to pressure transducers, which measure the air pressure at multiple locations over time. An electronic flow meter logs the airflow rate over time. These measurements enable direct calculation of air permeability as a function of water content. Due to the large number of air pressure and water content measurements along the length of the soil column, the air permeability functions of individual layers can be distinguished from the remainder of the soil core. Because all measurements are computer controlled and logged, the system is completely autonomous.