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Soil Science Society of America Journal Abstract -

Evaluation of the Relationship between Compressibility and Shear Strength of Andisols


This article in SSSAJ

  1. Vol. 57 No. 4, p. 923-929
    Received: May 6, 1992

    * Corresponding author(s):
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  1. D. H. McNabb  and
  2. L. Boersma
  1. Soils Branch, Alberta Environmental Centre, Bag 4000, Vegreville, AB, Canada T9C 1T4
    Dep. of Crop and Soil Science, Oregon State Univ., Corvallis, OR 97331



Andisols, and other soils with low bulk density, are often considered less susceptible to compaction than soils with higher bulk densities. This study was initiated to test the hypothesis that high soil strength reduces the compressibility of soils with low bulk density. The compressibility and shear strength of three Andisols were compared with that of a fine-textured soil of crystalline mineralogy with a higher bulk density. Soil compressibility was measured in one-dimensional consolidation tests and shear strength was measured in direct shear tests. Cores of undisturbed soil were collected from the 7- to 12-cm depth of four forested soils in western Oregon. Cores were saturated prior to testing. Compression indexes were 0.231 for the coarse-textured Andisol, 0.262 and 0.275 for two fine-textured Andisols, and 0.320 for the fine-textured soil of crystalline mineralogy, which was significantly higher than that of the Andisols. The angle of internal friction of the Andisols ranged from 33.0 to 33.7°, but was 28.9° for the fine-textured soil of crystalline mineralogy. A nonlinear model was successfully adapted to describe the relationship between bulk density and normal stress using data of these sample sets. These samples had different initial and compressed bulk densities. We concluded that Andisols are less compressible than other denser soils because of a high shear strength. The question of the susceptibility to compaction of soils with low bulk density must be reconsidered.

This is Paper no. 2859 of the Forest Research Lab., Oregon State Univ., Corvallis. This study was funded by the Forestry Intensified Research (FIR) Program in cooperation with the Bureau of Land Management, U.S. Forest Service, southwest Oregon counties and forest industries, and the Forest Research Lab., Corvallis.

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