Dual-platform micromechanical characterization of soils: Oscillation shear rheometry and spherical indentation

Reza Hosseinpour-Ashenaabad*, Thomas Keller, Mats Larsbo, Paul D. Hallett

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)
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The dynamics of soil structure is caused by biotic and abiotic processes, with the onset and magnitude of deformation controlled by soil rheological and mechanical properties. Quantification of such properties is challenging because soil behaviour changes with soil moisture, but common rheological tests are not applicable over all consistency ranges. Here, we combine oscillation shear rheometry with spherical indentation mechanical measurements of soil to obtain greater characterization over a broader range of water contents. The elastic modulus could be measured with either approach, with good agreement found for measured silt and clay textured remoulded agricultural soils. For shear rheometry, plastic viscosity, complex modulus and shear yield stress were also obtained. The spherical indentation provided measurements of hardness and yield stress. Although yield stress was correlated between approaches, the values were orders of magnitude greater for the indenter (0.54 +/- 0.33 kPa vs. 34.4 +/- 31.2 kPa), presumably because of different loading and failure conditions. At drier water contents, yield stress varied more between the two tests on the clay soil, which corresponded with brittle fracture creating artefacts in shear rheometry measurements. Spherical indentation has not been widely applied to the testing of soils, but the good agreement over a wide water content range between elastic modulus obtained from spherical indentation measurements (0.66 +/- 0.27 MPa in wetter zone to 4.45 +/- 2.53 MPa in drier zone) and shear rheometry (0.47 +/- 0.11 MPa in wetter zone to 2.02 +/- 0.98 MPa in drier zone) is promising. Moreover, spherical indentation can be applied to materials varying from brittle to viscous and allows testing on structurally intact soil aggregates. The geometry of a spherical indenter may more closely mimic contacting soil aggregates, so scope exists to extend the approach to explore the slumping of aggregated seedbeds produced by tillage.

Original languageEnglish
Article number105467
Number of pages12
JournalSoil & Tillage Research
Early online date27 Jun 2022
Publication statusPublished - Sept 2022

Bibliographical note

Funding from the NJ faculty at the Swedish University of Agricultural Sciences (SLU) is acknowledged for partly funding RH’s Ph.D. work. PH acknowledges funding from UKRI (BB/L026058/1, ES/T003073/1, NE/S009167/1) that supported background research that led to this study. This research was partly funded by the Faculty of Natural Resources and Agricultural Sciences (NJ Faculty) of the Swedish University of Agricultural Sciences.


  • Rheometry
  • Indentation
  • Micromechanics
  • Soil pastes
  • Viscoelasticity
  • Elastic modulus


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