In Geelong, we often see construction projects hit unexpected ground conditions because the soil profile shifts dramatically between the Barwon River flats and the volcanic basalt ridges to the north. A proper grain size analysis separates the coarse fraction from the fines, telling us exactly what we’re dealing with. Without that data, you’re guessing on compaction, drainage, and bearing capacity. We run both sieve and hydrometer methods in our NATA-accredited lab, covering particles from boulders down to 0.001 mm. For projects on the Bellarine Peninsula, where marine clays dominate, the hydrometer phase is critical. Complement this with a resistivity survey to map layer boundaries before drilling.
In Geelong’s mixed alluvial and basalt soils, a bimodal grading curve is common — sieve alone misses the clay fraction without hydrometer follow-up.
Scope of work in Geelong
Typical technical challenges in Geelong
The most common mistake we see in Geelong is relying solely on mechanical sieving for soils with high fines content. The Barwon River floodplain has silty clays with 40-60% passing the 75 µm sieve. If you skip the hydrometer, you classify it as silt when it actually behaves as a low-plasticity clay. That changes your compaction curves and your CBR estimates. We’ve seen road pavements fail within two years because the subgrade was treated as non-plastic. The hydrometer phase takes longer, but it’s the only way to get the real particle size distribution for fine-grained soils.
Our services
We offer two complementary testing services for grain size analysis in Geelong, both performed under NATA accreditation.
Mechanical Sieve Analysis
Dry and wet sieving for particles from 75 mm down to 75 µm. Suitable for sands, gravels, and crushed rock. Includes washing on the 75 µm sieve to remove fines before stacking. Results reported as cumulative percentage passing for each sieve size. Used for concrete aggregate, road base, and filter design.
Hydrometer Analysis
Sedimentation test for particles finer than 75 µm. Covers silt and clay fractions down to 0.001 mm using AS 1289 methodology. Includes dispersion with sodium hexametaphosphate, temperature correction, and meniscus adjustment. Essential for plasticity classification and compaction control in Geelong’s alluvial clays.
Frequently asked questions
What is the difference between sieve and hydrometer analysis?
Sieve analysis separates particles larger than 75 µm using stacked mechanical sieves. Hydrometer analysis measures the settling rate of particles smaller than 75 µm in a water column. Both are needed for a complete grain size distribution in soils containing clay and silt.
Why is grain size analysis important for Geelong construction?
Geelong has variable soil profiles — from sandy alluvium near the bay to stiff clays on the basalt plains. Grain size data determines compaction requirements, drainage characteristics, and bearing capacity. Without it, you risk differential settlement or pavement failure.
How long does a complete grain size analysis take?
Mechanical sieving takes about one working day. The hydrometer phase requires sedimentation readings over 24 hours, so a full analysis typically takes two to three business days. We prioritize urgent projects with same-day sieving if only coarse data is needed.
What is the cost range for grain size analysis in Geelong?
The typical range is between AU$140 and AU$270 per sample, depending on whether you require sieve only or sieve plus hydrometer. Volume discounts apply for multiple samples from the same project. Contact us for a firm quote based on your scope.