Brittle Fracture of Soil Aggregates and the Compaction of Aggregate Beds

Summary A statistical theory is developed for the brittle fracture of soil aggregates. Fracture is assumed to depend on the flaws, such as cracks and holes, within the aggregates, the weakest flaw limiting strength. An equation known as the third asymptote distribution of smallest values gives the distribution of these weakest flaws. The crushing strength of aggregates of five soils from South Australia and Queens land is compared with theory and agreement is good. Larger aggregates have smaller mean values of tensile strength than smaller aggregates at both ‐100 kPa and ‐153 MPa water potential. A sudden increase in strength occurs for aggregates larger than about 6 mm in the Queens land soils which is more marked with the drier samples. This is consistent with the idea that these larger aggregates are produced by the compacting effects of machinery, whereas the smaller aggregates are produced by the self‐mulching effect. Changes in the internal structure of beds of aggregates are described as a function of amount of uniaxial compaction. A statistical method gives information about the size distributions and relative positions of aggregates and voids within the compacted beds. Compaction occurred almost exclusively at the expense of inter‐aggregate porosity, and the largest voids were excluded first by compaction.