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Porosity Factors that Control the Hydraulic Conductivity of Soil‐Saprolite Transitional Zones
Author(s) -
Vepraskas M. J.,
Kleiss H. J.,
Amoozegar A.,
Guertal W. R.
Publication year - 1996
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1996.03615995006000010031x
Subject(s) - saprolite , geology , soil horizon , hydraulic conductivity , horizon , new horizons , porosity , soil science , mineralogy , soil water , geotechnical engineering , geometry , mathematics , aerospace engineering , engineering , spacecraft
Abstract Slowly permeable transitional horizons separate soil and saprolite, but these horizons cannot be identified easily in the field. The objectives of this study were to determine why the soil‐saprolite transitional zone (BC and CB horizons) is slowly permeable, and to evaluate ways for identifying it in the field. Two saprolite deposits were studied in the North Carolina Piedmont. At each site, saturated and unsaturated hydraulic conductivities ( K sat and K unsat ) were measured for major horizons. Volume fractions of water‐conducting pores were also compared with the changes in hydraulic conductivity with depth. Horizon mean K sat values at both sites ranged from virtually 0 to approximately 3 cm h ‐1 . The lowest K sat values (<0.3 cm h ‐1 ) occurred in or near the transitional horizons that were directly below the Bt horizons. Changes in the volume of pores within or between mineral grains (termed inter/intraparticle pores ) with depth corresponded to changes in both K sat and K unsat . In the transitional horizons, the inter/intraparticle pores were plugged with clay and this caused the horizons to have low K values. In situ measurements of K sat with depth were the most accurate technique to use for identifying transitional zones in the field. Examination of both the soil and rock structures in pits was also an acceptable technique. Texture and consistence were not considered reliable for pin‐pointing transitional horizons.