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A Method for Determining the Stability of Soil Structure Based Upon Air and Water Permeability Measurements¹

ABSTRACT

A method is described for determining the stability of soil structure based upon intrinsic permeability, the measurement being made first with air, and then with water. The change in permeability is attributable to the instability of the soil to the wetting and slaking action of the water.

Procedures and equipment for making tests with fragmented samples are described. Experimental data which show that the permeability ratio, air to water, is correlated with treatments known to produce differences in structural stability, are presented for both fragmented samples and soil cores. The air-water permeability ratio is shown to be correlated with both the exchangeable-sodium-percentage and clay content of soils. The effect of a polymeric soil conditioner of the type VAMA (Vinyl acetate-maleic acid) in stabilizing the structure of alkali soils, is reflected in the permeability ratio determination.

The permeability ratio for soils varies over a range of from slightly greater than 1 to 10,000 or more. This large range permits effective appraisal of soil treatments that affect soil stability.

On the basis of the reported tests, it appears that at the 20 to 1 level of odds, single determinations of the permeability ratio will distinguish a 45% difference for fragmented samples and a 185% difference for cores.

The permeability ratio expresses in a single dimensionless number the effects of many factors and processes that influence the stability of soil structure. It is an integrated measure of the effects of swelling, slaking, dispersion, and other processes that take place to change soil structure as a result of wetting with water.

¹ Contribution from the U. S. Salinity Laboratory, Riverside, Calif., and the Division of Soil and Plant Relationships, Beltsville, Md., BPISAE, U. S. Dept. of Agriculture in cooperation with the 17 Western States and the Territory of Hawaii.

² Agricultural engineer. The author is indebted to R. W. Austin for assistance with some of the exploratory measurements upon which this paper is based and for the assistance rendered in obtaining the experimental data reported in tables 3 and 4.

Received for publication May 23, 1953.