AS 1289.6.7.1 sets the benchmark for laboratory permeability testing in Australia, and in Bendigo it matters more than you might expect. The region's geology transitions from deep clay soils in the lowlands to sandy gravels near the former goldfields. That variability means a single permeability assumption for your site can be dangerously wrong. Our falling head test works well for the fine-grained soils typical of residential subdivisions in Kennington and Strathdale. For the coarser alluvial deposits found along Bendigo Creek, the constant head method gives you the reliable flow data needed for drainage design. Before we get to the lab stage, we often recommend a calicatas exploratorias to log the soil profile and select representative samples, then we pair the permeability result with a granulometria to confirm the grading curve. It is a straightforward sequence that removes guesswork from your earthworks or foundation planning.
A single permeability test on the wrong soil layer can mislead your drainage design by two orders of magnitude, especially in Bendigo's variable alluvial clays.
Methodology and scope
Take a typical 8-lot subdivision in Epsom. The contractor hits stiff clay at 1.5 m, but just 50 m away a test pit shows sandy silt. Without a lab permeability test on each soil type, the stormwater design either over-engineers the soakwells or under-sizes them. Here is how we run the process:
We extract undisturbed tube samples or bulk disturbed samples from your site.
In the lab, we saturate the specimen and apply a known hydraulic gradient under either falling head (for clays and silts, k < 10⁻⁴ m/s) or constant head (for sands and gravels, k > 10⁻⁴ m/s).
Results are reported as coefficient of permeability (k) in m/s, along with void ratio and test temperature.
We have run this sequence for over 200 Bendigo projects. The data feeds directly into retaining wall backfill specifications, pavement subgrade drainage, and septic system approvals. It is a small investment that saves rework when the first heavy rain arrives.
Technical reference image — Bendigo
Local considerations
Bendigo sits in a temperate climate with dry summers and winter rainfall averaging 500 mm annually, but the risk is not the total rain — it is how the ground behaves during those wet months. The expansive clays common around Golden Square and Kangaroo Flat can lose up to 80 % of their bearing capacity when saturated. If your laboratory permeability test misses the actual in-situ fabric (fissures, root holes, old mine workings), the k value reported will be too low and your soakwell will fail. That is why we insist on representative sampling and why we cross-check results with the soil classification before finalising the report.
Falling head (AS 1289.6.7.1) or constant head (AS 1289.6.7.2)
Sample type
Undisturbed tube (U50/U75) for clays; bulk disturbed for sands/gravels
Permeability range measured
1 x 10⁻⁹ to 1 x 10⁻² m/s
Reported parameters
Coefficient of permeability k, void ratio, test temperature, specimen dimensions
Typical turnaround
5–7 working days from sample reception
Accreditation
NATA ISO/IEC 17025 for permeability testing
Associated technical services
01
Falling head permeability (clays & silts)
For fine-grained soils with low hydraulic conductivity. We use undisturbed tube samples to preserve the natural structure and measure k under decreasing head conditions.
02
Constant head permeability (sands & gravels)
Applied to granular soils where flow rates are higher. The test maintains a steady hydraulic gradient and is ideal for drainage layer design and filter specification.
03
Combined permeability + classification suite
We bundle the permeability test with Atterberg limits and particle size distribution so you get a complete hydraulic and mechanical profile of the soil in one report.
Applicable standards
AS 1289.6.7.1 – Falling head permeability test, AS 1289.6.7.2 – Constant head permeability test, AS 1726 – Geotechnical site investigation
Frequently asked questions
What is the difference between falling head and constant head permeability tests?
Falling head is used for fine-grained soils like clays and silts where water flows slowly through the sample. The head of water decreases as it percolates, and we measure the time for a known drop. Constant head is used for sands and gravels where flow is faster; we maintain a steady water level and measure the volume collected over time. The right method depends entirely on the soil type found on your Bendigo site.
How much does a laboratory permeability test cost in Bendigo?
For a standard falling or constant head test on a single sample, the cost typically ranges between AU$620 and AU$1110. The variation depends on sample type (undisturbed tube vs. bulk disturbed), the number of tests, and whether you require a combined suite with classification tests. Contact us for a quote based on your specific scope.
Do you need undisturbed samples for the permeability test?
For falling head tests on clays, yes — an undisturbed tube sample (U50 or U75) is preferred because it preserves the natural fabric, fissures, and void ratio that control permeability. For constant head tests on sands and gravels, a bulk disturbed sample is usually sufficient because the granular structure is less sensitive to disturbance. We will advise on sampling method when you discuss your Bendigo project with us.
Can I use a laboratory permeability value for soakwell design in Bendigo?
Yes, but only if the sample is representative of the actual drainage layer. Bendigo soils can change from clay to sandy gravel within metres, especially near old mining areas. We recommend a minimum of one permeability test per soil stratum, and we always cross-check the lab k value against field observations. For critical soakwells, a field infiltration test on site may complement the lab data.
