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Soil Science Society of America Journal Abstract - SOIL PHYSICS

Compressibility of Repacked Soil as Affected by Wetting and Drying between Uniaxial Compression Tests


This article in SSSAJ

  1. Vol. 74 No. 5, p. 1483-1492
    Received: Oct 5, 2009

    * Corresponding author(s): beat.schaeffer@empa.ch
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  1. B. Schäffer *a,
  2. P. Boivinb and
  3. R. Schulinc
  1. a Inst. of Terrestrial Ecosystems, ETH Zurich, Universitaetstrasse 16, 8092 Zurich, Switzerland, currently at Empa, Swiss Federal Laboratories for Materials Science and Technology, Lab. of Acoustics/Noise Control, Überlandstrasse 129, 8600 Dübendorf, Switzerland
    b Agronomy-hepia, Univ. of Applied Sciences of Western, Switzerland, 150 route de Presinge, 1254 Jussy, Switzerland
    c Inst. of Terrestrial Ecosystems, ETH Zurich, Universitaetstrasse 16, 8092 Zurich, Switzerland


According to the classical concept of precompression stress, soil compaction increases precompression stress up to the maximum applied stress, while it leaves the compression index, i.e., the slope of the virgin compression line, unaffected. In field studies performed under unsaturated conditions, however, soil compaction was usually found to increase the precompression stress less than expected and to decrease the compression index. Our hypothesis was that this discrepancy may result from changes in the soil moisture status between compaction in the field and compression tests, including the common practice of preconditioning samples to a standard initial water potential for compression tests. To test this hypothesis, we performed confined uniaxial compression tests in which samples of repacked agricultural loamy topsoil were subjected to five compression cycles with increasing maximum stress. Part of the samples were subjected to a wetting–drying cycle and subsequently conditioned to water potentials of either −1, −6, or −30 kPa before each of Compression Cycles 1, 3, and 5, while the other samples were conditioned to these water potentials only before Cycle 1 and not subjected to any wetting–drying cycles. The concept of precompression stress was found to be fully valid as long as the samples were not subjected to wetting–drying cycles and not reconditioned between compression events. In contrast, the wetting–drying cycles and sample conditioning between compression events reduced both the precompression stress and the compression index. Such effects are not accounted for by the classical concept of precompression stress.

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