AN INSTRUMENT FOR THE IN-SITU CHARACTERIZATION OF SOIL STRUCTURAL STABILITY BASED ON THE RELATIVE INTRINSIC PERMEABILITIES TO AIR AND WATER

The predominant methods of measuring soil structural stability are con fined to laboratory methods that, by their nature, do not quantify the field stability of the soil. An instrument is presented here for meas uring the soil structural stability in situ. Stability is assessed by a method based on the change in structural characteristics that may oc cur when the soil is permeated by non-interactive and interactive flui ds. The instrument utilises air (at small pressure) and water as these respective permeating fluids. A ratio of the intrinsic permeability o f the soil to these two fluids (k(a)/k(w)) is then used as a structura l stability index, with unity representing fundamental stability. Base -line data using a relatively stable sand medium, and in situ site dat a from several soil types in New South Wales, Australia, display an in dex ranging from 6 to 574. Analysis of the data shows significant diff erences in k(a)/k(w) values between soil types and management practice s. The effect of within-site sample mutual correlation on the signific ance tests is assessed and sampling technique is discussed. Comparison with results obtained using a qualitative field test for aggregate st ability and a laboratory-based stability index is shown.