A Handheld Device for Intrusive and Nonintrusive Field Measurements of Air Permeability

Abstract

Air permeability is an easy to measure soil parameter that is of direct importance in gas transport studies. Its values can also be used as indicators of soil hydraulic conductivity. Near the soil surface, both air and water permeability values are important for hydrological and agricultural studies involving, for example, soil aeration and water runoff during rainfall events. We provide a design of a rugged, lightweight, handheld, single-reading device allowing for fast measurements of air permeability near the soil surface. The device makes use of two interchangeable air probes. The contact probe, well documented in the petroleum engineering literature, is proposed as an addition to the traditional insertion probe. The advantages and drawbacks of each probe type are discussed briefly. Central to the in situ measurement of air permeability is the concept of the probe geometric factor. Empirical relationships are presented to make the application of this concept more amenable. Relative differences in air permeability values obtained with the two probes seem to be acceptable for permeability measurements. Even though in most cases contact probe air permeability values were higher than insertion probe values, no clear trend existed. The differences were attributed to differences in soil compaction, bypass flow, and different measurement volumes associated with the two probe types. For the flow rates and pressures encountered during the measurements, the flow rate behaved as a linear function of the pressure gradient. In other words, the assumed Darcy-type equation was applicable.