Mackay sits on the coastal floodplain of the Pioneer River, where more than 80,000 residents live on a mix of alluvial sands, estuarine clays, and residual soils from the surrounding volcanic ranges. That geological diversity makes grain size analysis a non-negotiable first step for any project here, whether you are building a retaining wall along the riverbank or a residential slab on the northern suburbs. We run the full sieve and hydrometer procedure in our NATA-accredited laboratory, separating particles from gravel down to colloidal clay fractions. The results feed directly into soil classification under the Unified Soil Classification System and the AS 1726 framework. Without this data, your geotechnical model is just an educated guess, and in Mackay's variable ground conditions that guess can cost you thousands in rework or foundation over-design.
In Mackay's alluvial and estuarine deposits, the fine fraction can exceed 60 percent, making hydrometer analysis essential for accurate soil classification.
Methodology and scope
One thing we see regularly in Mackay is that the fine fraction in the estuarine clays can spike above 60 percent, which completely changes how the soil behaves under load and during wetting-drying cycles. Our sieve analysis handles particles down to 75 microns, while the hydrometer test picks up the silt and clay fractions below that threshold. We follow AS 1289.3.6.1 for the mechanical sieving and AS 1289.3.6.3 for the sedimentation phase, ensuring every result is reproducible and defensible. The real value for your project comes when we correlate the grain size curve with other engineering properties. For example, combining grain size data with a plasticity index from the Atterberg limits gives you a reliable basis for estimating shrink-swell potential in Mackay's reactive clays.
Dry sieving for coarse fractions (gravel and sand)
Wet sieving to remove fines before hydrometer
Sedimentation analysis using AS 1289.3.6.1 methodology
Hydrometer corrections for temperature and dispersant
Technical reference image — Mackay
Local considerations
The equipment we mobilise for grain size testing in Mackay includes a stack of sieves from 75 mm down to 75 microns on a mechanical shaker, plus a thermostatically controlled sedimentation bath for the hydrometer phase. The hydrometer itself is a calibrated ASTM 152H model, read at timed intervals over 24 hours to capture the full settlement of clay particles. In a town where tropical rain can dump 200 mm in a single afternoon, getting undisturbed samples to the lab quickly is critical — fines can flocculate or wash out if not handled correctly. We use sealed plastic bags and rigid containers for transport, and we log every sample against the chain of custody. The risk of misclassifying a soil because the fines fraction was understated is real, especially when the design relies on drainage assumptions or settlement estimates.
Full mechanical sieving from 75 mm down to 75 microns, with wet sieving when the fines content exceeds 15 percent. We report the cumulative passing curve and the coefficients of uniformity (Cu) and curvature (Cc) for each sample.
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Hydrometer Sedimentation Test
Quantitative determination of the silt and clay fractions below 75 microns using the ASTM 152H hydrometer. The test runs over 24 hours with corrections for temperature, dispersant, and meniscus, giving you the full particle size distribution down to 0.5 microns.
Applicable standards
AS 1289.3.6.1 — Sieve analysis of soils, AS 1289.3.6.3 — Determination of the particle size distribution of a soil — Standard method of fine analysis using a hydrometer, AS 1289.3.6.1(2007) — Standard Test Method for Particle-Size Analysis of Soils, AS 1726 — Geotechnical site investigations
Frequently asked questions
Why do I need both sieve and hydrometer analysis for my Mackay project?
The sieve alone stops at 75 microns, but Mackay's estuarine clays contain significant material below that threshold. The hydrometer captures the silt and clay fractions down to 0.5 microns, which directly affect settlement estimates, drainage design, and shrink-swell behaviour. Without the hydrometer, you might classify a high-plasticity clay as a low-plasticity silt, leading to an under-designed foundation.
What is the typical turnaround time for grain size analysis in Mackay?
Standard turnaround is 5 to 7 business days from sample receipt. The hydrometer phase requires a full 24-hour sedimentation reading, so same-day results are not possible. If you need faster service, we can prioritise the sieve portion in 2 days and provide the hydrometer results later as a supplementary report.
How much does grain size analysis cost in Mackay?
The typical cost for a combined sieve and hydrometer analysis is between AU$170 and AU$300 per sample, depending on the number of fractions required and whether wet sieving is needed. Bulk discounts apply for projects with more than ten samples. Contact us for a quote tailored to your scope.
Can you correlate grain size results with other geotechnical parameters?
Yes. The particle size distribution curve feeds directly into the USCS classification, which then informs estimates of permeability, compressibility, and shear strength. We routinely cross-reference grain size data with Atterberg limits and in-situ density tests to build a reliable geotechnical model for your site.
