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Undisturbed Sampling (Shelby Tube) in Melbourne, Victoria

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AS 1726 sets the standard for undisturbed soil sampling in Australia, and in Melbourne that standard matters more than most realise. The city sits atop a deep sequence of Quaternary sediments, including the Fishermens Bend Silt and Coode Island Silt, formations known for their high sensitivity and low shear strength. Undisturbed sampling (Shelby tube) is the only reliable method to extract intact specimens from these soft clays without altering moisture content or fabric. Before committing to foundation design, engineers typically correlate Shelby tube results with a CPT to validate stratigraphy, or use a dilatometer when stiffness parameters are needed for settlement analysis. The combination gives Melbourne practitioners a complete picture of sub-surface behaviour.

Illustrative image of Undisturbed sampling (Shelby tube) in Melbourne

Without undisturbed sampling, Melbourne's soft clay settlement can be underestimated by 40% or more in design calculations.

Our service areas

Ground improvement

Unsaturated soil analysis ›Stone column design ›Dynamic compaction design ›Deep Soil Mixing (DSM) design ›Geotechnical drainage design ›

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Slopes & Walls

Soil erosion analysis ›Slope stability analysis ›Slope failure analysis ›Debris flow analysis ›Factor of safety (FS) calculation ›

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Foundations

Differential settlement analysis ›Settlement analysis ›Bearing capacity analysis ›Foundations on fill (analysis) ›Shallow foundation design ›

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Methodology and scope

A local geotechnical team knows that Melbourne's urban infill often covers old creek channels and estuarine deposits. In those settings, a thin-walled Shelby tube pushed hydraulically into the borehole base preserves the soil's in-situ structure far better than split-spoon methods. The sampler must penetrate smoothly at a constant rate — typically 0.3 to 0.5 metres per second — to minimise disturbance. Once retrieved, the tube ends are sealed immediately with wax or plastic caps to retain moisture. Key parameters derived from these undisturbed samples include:

Undrained shear strength (su) via triaxial or vane tests
Consolidation characteristics (Cc, Cv)
Sensitivity (St) for evaluating brittle behaviour
Atterberg limits on truly intact material

Technical reference — Melbourne

Local considerations

Melbourne's variable water table, which fluctuates seasonally from 1.5 to 4 metres depth across the metropolitan area, creates a real risk of sample disturbance during extraction. If the tube is withdrawn too quickly, suction at the base causes tensile cracking in the clay — the sample becomes unusable for consolidation testing. The coastal humidity also accelerates moisture loss from open tubes. That is why field crews in Melbourne use immediate wax sealing and transport samples in humidified containers. Missing any of these steps compromises the entire laboratory programme and can lead to unconservative foundation designs.

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Applicable standards

AS 1726-2017 Geotechnical site investigations, AS 1289.6.0 Standard Practice for Thin-Walled Tube Sampling, AS 1289.0-2014 Methods of testing soils for engineering purposes

Technical parameters

Parameter	Typical value
Sample diameter (Shelby tube)	73 mm or 89 mm
Maximum sampling depth	30 m (typical rig limit)
Tube wall thickness	1.2 mm (thin-wall per AS 1726)
Area ratio (tube)	≤ 10% for low-disturbance
Recovery ratio target	> 95%
Storage before testing	≤ 14 days in sealed tube

Frequently asked questions

How much does undisturbed sampling (Shelby tube) cost in Melbourne?

Typical project costs range from AU$650 to AU$1,680 per sample, depending on depth, access constraints, and the number of tubes required. Bulk discounts apply for multi-borehole programs. A formal quote is issued after reviewing site conditions and the required testing suite.

What is the difference between undisturbed and disturbed samples?

An undisturbed sample preserves the in-situ density, moisture content, and soil structure — essential for consolidation and strength tests. A disturbed sample (e.g., from SPT split-spoon) is only suitable for classification, moisture content, or compaction tests. In Melbourne's soft clays, using a disturbed sample for settlement analysis can lead to significant error.

How do you prevent sample disturbance in Melbourne's soft clays?

We use thin-wall Shelby tubes with an area ratio below 10%, advance the sampler hydraulically at a steady rate of 0.3 to 0.5 m/s, and seal tubes immediately with wax caps. The samples are transported upright in temperature-controlled containers to minimise vibration and moisture loss.

Location and service area

We serve projects across Melbourne.

Location and service area