Rockhampton grew on the banks of the Fitzroy River, a setting that shaped its soil profile. Floodplain silts and clays sit alongside weathered basalt from the Berserker Range. Understanding how water moves through these layers is critical for foundation design and earthworks. We perform laboratory permeability tests using falling and constant head methods to determine hydraulic conductivity. These tests follow AS 1726 and are run on undisturbed or remoulded samples. The data helps predict drainage behaviour and seepage rates. For projects involving cut slopes, we often combine this analysis with a falla-taludes assessment. On sites with soft ground, results also support decisions on drenes-verticales spacing.
In Rockhampton's clay soils, a k value below 1x10⁻⁹ m/s often indicates very low drainage — critical for slope stability.
Scope of work
Area-specific notes
Rockhampton sits about 20 metres above sea level, but the Fitzroy River floodplain is prone to inundation after heavy cyclonic rain. High permeability in shallow sand layers can lead to rapid groundwater rise beneath slabs and foundations. If drainage is underestimated, hydrostatic pressure may build up behind retaining walls or under floor slabs. A laboratory permeability test provides a controlled measurement of hydraulic conductivity. This data is essential for designing subsoil drainage systems and assessing the risk of water softening in reactive clays. We have tested samples from the Koongal and Depot Hill areas where these issues are common.
Standards used
AS 1289.6.7.1 Falling head permeability test, AS 1289.6.7.2 Constant head permeability test, AS 1726 Geotechnical site investigations
Linked services
Falling Head Permeability Test
Used for fine-grained soils with low hydraulic conductivity. A standpipe is attached to the sample and the rate of water level drop is recorded. Results are expressed as coefficient of permeability k. Suitable for clays and silts from Rockhampton's alluvial and residual profiles.
Constant Head Permeability Test
Applied to coarse-grained soils where flow is higher. Water is supplied at a constant head and the volume passing through the sample is measured over time. Ideal for sands and gravels from river terrace deposits near the Fitzroy.
Typical parameters
FAQ
What is the difference between falling head and constant head permeability tests?
Falling head is used for low-permeability soils like clays and silts. Constant head is for high-permeability soils like sands and gravels. The choice depends on the expected flow rate through the sample.
How much does a laboratory permeability test cost in Rockhampton?
The typical range is between AU$560 and AU$1020 per test. Costs vary with sample preparation, number of specimens, and whether falling or constant head method is used.
How long does the test take?
A falling head test on clay can take 5 to 14 days due to slow flow. Constant head tests on sand may be completed in 1 to 3 days. Saturation and consolidation stages add time.
What sample types are accepted?
We accept undisturbed tube samples (50 mm or 100 mm diameter), block samples, and remoulded specimens compacted to target density. Samples must be sealed and labelled with depth and location.