Swelling of a clay soil profile under ponding

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Abstract
The total vertical swelling under long-term ponding, of two apparently identical soil profiles, into one of which gypsum had been incorporated, is described. The effect of gypsum per se was minor, and reduced swelling only near the surface. Its indirect effect was to allow more water entry, which in turn increased the swelling of deeper soil. Total and incremental swelling to a depth of 2.10 m, and water absorption, are analysed in terms of models of swelling and shrinking. Except for the interval 0.25-0.55 m in the untreated profile, swelling was not normal, the water absorbed being somewhat greater than themeasured swelling. It is concluded that, particularly in the profile with gypsum, macropores contained an appreciable amount of water which did not contribute to swelling; others have called this structural water, and the macropores, structural pores. The likely types of macropore, as described in micromorphology, are indicated.