In Australia, the compaction test for soil is conducted in accordance with the Australian Standard AS 1289.5.1.1:2018.
It provides detailed specifications for the compaction test equipment, compactive effort, sample preparation, and calculations to ensure consistent and accurate results. It is a widely recognised standard used by geotechnical engineers and soil testing laboratories across Australia for evaluating the compaction properties of soils.
Most common compaction test
Confirmation of the specified compaction level is typically evaluated by conducting a laboratory test called the Proctor compaction test, also known as the Standard or Modified Proctor test. This test provides a reliable and standardised method for determining the maximum dry density (SMDD) and optimum moisture content (%) of a soil.
During the Proctor test, a soil sample is compacted in a controlled manner using specified compactive efforts and moisture contents. The process generally involves:
- Obtaining a soil sample from the field and collecting it at different depths or alignments.
- The soil sample is screened over a sieve to determine the size of the compaction mould required, then the sample is divided and mixed with specific moisture contents at a range of moisture contents that straddles dry and wet from the estimated optimum moisture contents.
- The subsamples are then compacted in a compaction mould using the same compactive effort either by a manual standard compaction hammer or automatic mechanical equipment.
- The compacted samples are then weighed, divided by the known volume of the mould to determine the wet density (t/m3) at each compaction point. The moisture content is determined for each compaction point to determine the dry density (t/m3).
- Each dry density and moisture content value are plotted on a graph, known as the compaction curve (parabola curve), which shows the relationship between moisture content and dry density.
By analysing the compaction curve, engineers can determine the moisture content that yields the maximum dry density, referred to as the optimum moisture content. The achieved maximum dry density at the optimum moisture content is compared to the field in situ density. The field dry density divided by the laboratory maximum dry density gives the density ratio, expressed as a percentage.
The Proctor compaction test provides valuable information for assessing the suitability of the soil for construction and designing foundations, embankments, and other structures.
Douglas Partners can provide compaction testing services during construction to verify that the soil has been compacted in accordance with the specification. Learn more here.
