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Strength Characteristics of Three Indurated Horizons in Massachusetts¹

ABSTRACT

Identification of fragipans is often difficult due to the lack of quantitative differentiating criteria. The unconfined compression (UC) test was used to characterize strength properties of three indurated horizons. Tests were performed in the laboratory on undisturbed core samples equilibrated to one of four moisture conditions: wet, 0.1 MPa, 0.5 MPa, or air-dried. Fragipans developed in basal till exhibited maximum UC strength values of about 100 kPa at moisture contents < 0.10 kg kg^–1 and minimum UC strength of < 25 kPa at wetnesses of 0.14 kg kg^–1 or more. Between these two critical moisture contents, strength varied inversely with wetness. A pan formed in post-glacial colluvial deposits showed similar maximum UC strength values but still retained about 70% of its UC strength at the wet moisture condition. The UC testing data enabled separation of the fragipans developed in the glacial till from indurated horizons formed in the colluvial material. Pocket and Proctor penetrometers were investigated to determine their suitability for routine recognition of fragipan horizons in the field, especially during wet soil conditions. Their application did not improve upon current field techniques.

¹ Contribution from the Massachusetts Agric. Exp. Stn. (Paper no. 2564), Dep. of Plant & Soil Sci., Univ. of Massachusetts, Amherst, MA 01003.

² Graduate Research Assistant and Associate Professor of Soil Science, respectively.

Received for publication March 15, 1983. Accepted for publication August 27, 1983.