Shepparton sits on the Goulburn River floodplain, where the topsoils are silty clays and the water table sits at 2–4 m depth depending on the season. That moisture variability directly influences compaction targets. We run the Proctor test (Standard and Modified) on samples from every exploratory pit or borehole to determine the optimum moisture content and maximum dry density before any earthworks begin. Without that data, achieving the specified compaction ratio becomes guesswork. The local clay profiles tend to be highly plastic, so we also cross-check results with Atterberg limits to confirm the soil is within the workable moisture range for rolling and compaction.
Compaction curves from Shepparton's alluvial clays typically show optimum moisture near 18 % – missing that by 2 % can drop density by 5 %.
Method and coverage
- Air-drying the bulk sample until it reaches the target moisture increment
- Compacting in three layers (Standard) or five layers (Modified) with 25 blows per layer
- Weighing the mould, extruding the soil, and oven-drying a slice to measure actual water content
Regional considerations
The main compaction risk in Shepparton is moisture sensitivity. The alluvial clays shrink and swell rapidly with water content changes. If the Proctor curve is not obtained before bulk earthworks, the contractor may roll a subgrade that looks firm but fails the 95 % or 98 % density test after a wet spell. We have seen cases where a 3 % overshoot in moisture content caused 12 mm of differential settlement under a warehouse slab within six months. The Modified Proctor is especially important for road pavements on the Goulburn Valley Highway upgrades, where heavy truck loading demands a high-density, low-air-voids fill. Complementing the Proctor with subgrade testing on the same material gives a direct relation between compaction effort and CBR strength.
Standards that apply
AS 1289.5.1.1 – Soil compaction and density tests: Standard Proctor, AS 1289.5.2.1 – Soil compaction and density tests: Modified Proctor, AS 1726 – Geotechnical site investigations (sampling requirements)
Complementary services
Standard Proctor (AS 1289.5.1.1)
Low-energy compaction curve for residential slabs, light-duty pavements, and trench backfill. Includes moisture-density relationship and reporting of maximum dry density (MDD) and optimum moisture content (OMC).
Modified Proctor (AS 1289.5.2.1)
High-energy compaction curve for heavy-traffic roads, airport aprons, and industrial floors. Typically specified for Shepparton's arterial road projects and large-scale subdivision earthworks.
Compaction Curve + CBR Correlation
Proctor curve plus soaked and unsoaked CBR on the same sample at OMC. One integrated report saves time when designing pavement thickness under the Austroads pavement design guide.
Typical parameters
Top questions
What is the difference between Standard and Modified Proctor for Shepparton soils?
Standard Proctor uses 595 kJ/m³ of compaction energy, suitable for residential fills and low-traffic areas. Modified Proctor applies 2700 kJ/m³, matching the higher compactive effort of heavy rollers used on state road projects. Shepparton's silty clays often show a 3–5 % lower OMC and 0.05–0.10 t/m³ higher MDD under Modified effort.
How much does a Proctor test cost in Shepparton?
A single Standard Proctor test ranges from AU$140 to AU$220, and a Modified Proctor from AU$200 to AU$320. The price depends on sample quantity and whether you need the curve plus CBR in one run. We issue a NATA-endorsed certificate with each test.
How many samples do I need for a typical subdivision in Shepparton?
For a 20-lot subdivision, we recommend one Proctor test per soil type encountered – usually 3 to 5 tests covering the topsoil, clay subgrade, and any imported fill. Each test requires about 25 kg of bulk sample. If the material changes across the site, additional tests are needed to keep compaction control valid.