Soil precompression stress I. A survey of Swedish arable soils

In determining stress limits to prevent soil compaction, it is important to know the mechanical properties of soils. One important parameter is the precompression stress, which is often used as a criterion for soil susceptibility to compaction. A series of uniaxial compression tests on Swedish arable soils was conducted by Eriksson [Markpackning och rotmiljo (soil compaction and root environment), Report 126, Division of Agricultural Hydrotechnics, Department of Soil Sciences, Swed. Univ. Agric. Sci., Uppsala, Sweden, 1982 (in Swedish, with English summary)]. The objective of the present study was to derive precompression stress values from these data. Eighteen soils, generally classified as Eutric Cambisols and with clay contents ranging from 62 to 863 g kg(-1) were used. Soil cores (25 mm high, 72 mm in diameter) were sampled at 10 cm intervals to a depth of I m and equilibrated at 0.5 or 60 kPa water tension. The cores were then compressed in an oedometer by sequential stresses of 25, 50, 100, 200, 400 and 800 kPa. Precompression stress was determined according to Casagrande [The determination of the pre-consolidation load and its practical significance, in: Proceedings of the International Conference on Soil Mech. and Found. Eng. (ICSMFE), vol. 3, Cambridge, MA, 22-26 June 1936, pp. 60-64] and by regression methods. Precompression stress was higher for subsoils than for topsoils and higher at higher soil water tension, but was difficult to relate to soil physical properties. Values determined according to Casagrande were generally between 100 and 200 kPa. Values determined by regression methods had a smaller range compared to the Casagrande method. The values of precompression stress indicate a low risk for subsoil compaction on Swedish soils, which is not in line with practical experience in compaction experiments. The concept of precompression stress as a clear transition from small, elastic deformation to larger, plastic deformation could not be supported by the stress-strain relationships obtained in this study. There is an urgent need to design laboratory tests that reflect soil behaviour in the field.. (C) 2004 Elsevier B.V. All rights reserved.