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SOIL PHYSICS

Testing Soil Encasing Materials for Measuring Hydraulic Conductivity of a Sandy-Loam Soil by the Cube Methods

Dipartimento di Ingegneria e Tecnologie Agro-Forestali, Facoltà di Agraria, Università degli Studi, Viale delle Scienze, 90128, Palermo, Italy

^* Corresponding author (bagav{at}unipa.it).

The Cube Method (CM) and the Modified Cube Method (MCM) were developed for measuring vertical (K_v) and horizontal (K_h) saturated hydraulic conductivity of a single soil sample. By these methods, a cube of soil is carved out in situ and a suitable material is applied to enclose the cube in a tightly fitting casing before moving the sample to the laboratory. Problems may be associated with the use of gypsum, originally used to encase soil. The suitability of molten wax and expandable polyurethane foam to encase a soil cube was tested for a sandy-loam soil. Wax-treated samples yielded lower conductivity results than untreated samples by a maximum factor of 3.7. The observed discrepancies were attributed, at least in part, to soil pore obstruction phenomena caused by wax. Using foam to fill a gap 60% full and partially preventing leakage of expanded foam from the gap was found to be appropriate to reach the following objectives: (i) filling completely the gap after foam expansion, (ii) preventing flow at the boundary between the foam cast and a smooth surface, (iii) minimizing both dry and wet soil compaction phenomena during foam expansion, (iv) minimizing foam intrusion into exposed pores of 1.0 x 10^–3 to 3.0 x 10^–3 m (intrusion depth 2.0 x 10^–3 m), and (v) allowing removal of any intrusion by the detachment of the set foam from the treated surface. Applying foam to collect undisturbed soil samples yielded K_v results (7.41 x 10^–5– 1.67 x 10^–4 m s^–1) falling in the range of a larger number of previously measured conductivities (2.06 x 10^–5– 2.03 x 10^–4 m s^–1), and it showed that K_v was 2.3 times larger than K_h. In conclusion, using wax is not recommended to obtain fully representative soil samples. Foam was a promising encasing material for the investigated soil.

Abbreviations: CHP, constant-head laboratory permeameter • CM, Cube Method • K_h, horizontal saturated hydraulic conductivity • K_v, vertical saturated hydaulic conductivity • MCM, Modified Cube Method • NT, untreated soil cores • SFH, simplified falling head • TCM, Two-Core Method • W, wax-treated soil cores