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ORIGINAL RESEARCH

A Dynamic Air Permeameter for Coarse-Textured Soil Columns and Cores

Biosyst. Eng. and Environ. Sci., The Univ. of Tennessee, 2506 E. J. Chapman Drive, Knoxville, TN 37996
^* Corresponding author (jtyner{at}utk.edu)

Received 21 June 2004.

The objective of this research was to develop a rapid method to measure the air permeability of multiple layers of a coarse-textured soil column or core. The method required dry air to be pumped through an initially wet soil column, which evaporated the water from the soil within 24 to 48 h. During the drying process, the airflow rate was recorded, and the air pressure was measured at multiple locations along the length of the column. Concurrently, a -ray system was employed to collect water content and dry bulk density measurements. The air permeability as a function of water content was then calculated for each measured interval along the length of the soil column. The method was applied to a hand-packed soil sample intended to be as homogenous as possible, and it was shown that small variations in bulk density contributed to measurable variation in the resulting air permeability. A two-layer, hand-packed soil sample was similarly tested, and the method clearly identified the air permeability of both layers. The method was also successfully performed on an intact heterogeneous field sample collected in a brass sampling tube. Measured air permeabilities from the three tests ranged from 9.8 x 10^–13 to 2.1 x 10^–10 m². The method is not appropriate for fine-textured soils or those that shrink significantly when dried.

Abbreviations: k_a, dry air permeability • Q, volumetric airflow rate • RH_in, inlet relative humidity • RH_out, outlet relative humidity • L, sample length • P, differential pressure • , volumetric water content • _db, dry bulk density