AS 1726:2017 sets the standard for in-situ testing in Australia, and the field vane shear test (VST) is the go-to method for measuring undrained shear strength in soft clays. Bendigo's geology, with its deep alluvial deposits in the Bendigo Creek valley and around Lake Weeroona, means many sites encounter low-strength saturated clays that can't be sampled undisturbed. We've used the VST on residential subdivisions near Epsom and commercial projects in the CBD to confirm design parameters before piling or slab-on-grade. Combining VST results with a [MASW survey](/masw-vs30/) gives a clearer picture of stiffness profiles across the site.
The field vane shear test delivers undrained shear strength in soft clays where undisturbed sampling fails — critical data for Bendigo's alluvial deposits.
Methodology and scope
Comparing the old goldfields around Ironbark with the floodplain near White Hills reveals stark differences in ground behaviour. The former has stiff residual soils; the latter has soft, compressible clays where a Vane Shear Test becomes essential. We run the test following AS 1289.6.2.1, using a 65mm vane for soft clays and a 38mm vane for firmer layers. The procedure is quick: advance the vane to test depth, rotate at 6°/min, and record peak torque. For low-sensitivity clays we also measure remoulded strength. This data feeds directly into bearing capacity calculations and slope stability checks. When we need additional shear strength profiles, we pair the VST with a dilatometer test for more detailed modulus values across the site.
Technical reference image — Bendigo
Local considerations
Bendigo sits on Ordovician bedrock overlain by up to 15 metres of alluvial clay, sand, and gravel in the valley floors. The water table is shallow near Bendigo Creek, often within 2–3 metres of the surface. Soft clay layers in these zones can have undrained shear strengths below 20 kPa — too weak to support shallow footings without improvement. Skipping the field vane shear test in these conditions risks differential settlement exceeding 25 mm, which cracks brick veneer and slabs. We've seen it happen on two housing projects in Kangaroo Flat where fill was placed without shear strength verification.
Full vane shear testing in low-strength alluvial clays. Includes peak and remoulded strength measurements, sensitivity index, and a certified report with Su vs depth profile.
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VST for Slope Stability & Embankments
Targeted testing along planned cut slopes and fill embankments. We correlate VST results with stability analysis to confirm safety factors per AS 4678.
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VST with Inclinometer Monitoring
Combined service: VST to establish baseline shear strength plus inclinometer casing installation for long-term deformation monitoring. Ideal for landfill or levee projects.
Applicable standards
AS 1726:2017 – Geotechnical site investigations, AS 1289.6.2.1 – Standard test method for field vane shear test, AS 4678:2002 – Earth retaining structures
Frequently asked questions
What is the difference between a field vane shear test and a laboratory triaxial test?
The VST measures undrained shear strength in situ without disturbing the soil fabric, which is critical for soft clays that are nearly impossible to sample intact. A triaxial test requires undisturbed samples and measures shear strength under controlled drainage conditions. In Bendigo's soft alluvial clays, the VST often gives lower and more realistic Su values because it avoids sample disturbance.
How deep can a field vane shear test reach in Bendigo's soils?
With standard extension rods and a track-mounted or truck-mounted rig, we routinely reach 30 metres in Bendigo. Most tests are shallower — between 3 and 15 metres — because that's where the soft alluvial clays sit. Deeper tests are possible if the vane can penetrate without rod buckling, but we rarely need to go beyond 20 metres in this region.
How much does a field vane shear test cost in Bendigo?
The cost for a field vane shear test in Bendigo typically ranges between AU$1,000 and AU$2,360 depending on depth, number of test points, and site access. We provide a fixed-price quote after a quick site visit. Mobilisation is included for sites within 30 km of Bendigo's CBD.
When should I choose a VST over a CPT or SPT?
Choose the VST when the ground is soft clay (Su < 50 kPa) and you need undrained shear strength directly. The CPT gives a continuous profile but requires correlation to estimate Su. The SPT is unreliable in soft clays because the spoon displaces the soil. For Bendigo's alluvial flats, we often run VST at discrete depths alongside a CPT to calibrate the cone factor.
