Scaling of the structure and strength of soil aggregates

PD Hallett*, AR Dexter, NRA Bird, JPK Seville

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

In this study we provide experimental evidence to support concepts concerning the scaling of soil strength and pore structure over a range of aggregate sizes. The aggregates were obtained by the repetitive fracture of larger soil aggregates. This ensured that the smaller aggregates studied were the building blocks of the larger aggregates. Sieving tilled soil to obtain a range of aggregate sizes introduces artifacts due to stresses imparted during tillage and due to the different effects of wet/dry cycles on aggregates of different sizes.

Aggregate strength was measured by the indirect tension test. The measurements of pore structure are (a) specific volume, (b) the pore size distribution by mercury porosimetry, (c) the pore size distribution measured on thin-sections, and (d) the proportion of the fracture surface consisting of pre-existing cracks. In the latter approach, incipient cracks in soil that link up during fracture were stained using methylene blue dye. Scaling of all pore structure properties is assessed using fractals.

For the three soils tested, aggregate strength increased with decreasing aggregate size. A log-log relationship between aggregate size and strength is found from which both friability and a fractal dimension are determined. Measurements of pore structure scaling suggest that fewer pores are available for crack propagation with decreasing aggregate size. Specific volume and the proportion of pre-existing cracks on fracture surfaces both decreased as aggregate size decreased. Analysis of thin-sections and measurements of pore-size distributions using mercury porosimetry suggest that only the few largest cracks form incipient interaggregate fracture surfaces and control the strength.

The results are consistent with the concept that aggregate strength scaling is dependent upon pore structure scaling. A comparison of aggregate strength with the amount of pre-existing cracks on the fracture surfaces shows that fracture occurs because of crack propagation. Further research examining the mechanisms of crack propagation in soil is required to determine a physical relationship between pore structure and strength scaling in soil aggregates.

Original languageEnglish
Title of host publicationSUBSOIL COMPACTION: DISTRIBUTION, PROCESSES AND CONSEQUENCES
EditorsR Horn, JJH VandenAkker, J Arvidsson
Place of PublicationREISKIRCHEN
PublisherCATENA VERLAG
Pages22-31
Number of pages4
ISBN (Print)3-923381-44-1
Publication statusPublished - 2000
EventInternational Workshop on Subsoil Compaction - KIEL, Germany
Duration: 1 Mar 1999 → …

Publication series

NameADVANCES IN GEOECOLOGY
PublisherCATENA VERLAG
Volume32

Conference

ConferenceInternational Workshop on Subsoil Compaction
CountryGermany
CityKIEL
Period1/03/99 → …

Keywords

  • FRACTURE
  • aggregate
  • soil structure
  • PARTICLES
  • strength
  • fracture
  • scaling

Cite this

Hallett, PD., Dexter, AR., Bird, NRA., & Seville, JPK. (2000). Scaling of the structure and strength of soil aggregates. In R. Horn, JJH. VandenAkker, & J. Arvidsson (Eds.), SUBSOIL COMPACTION: DISTRIBUTION, PROCESSES AND CONSEQUENCES (pp. 22-31). (ADVANCES IN GEOECOLOGY; Vol. 32). CATENA VERLAG.