The Wykeham Farrance loading frame we use for the unconfined compression test in Hervey Bay sits in our temperature-controlled lab on the Fraser Coast. We set the cylindrical specimen — trimmed from undisturbed tube samples — between the platens and apply axial load at a constant strain rate of 1% per minute. The proving ring dial gauge gives us the load at failure, and the built-in displacement transducer records axial strain simultaneously. For soft clays typical of the Pialba formation, we often run the test at a slower rate to capture the stress-strain curve properly. This method follows AS 1726-2017 clause 5.3.2 exactly, ensuring results are defensible for foundation design in Hervey Bay's coastal environment.
For Hervey Bay's soft coastal clays, the unconfined compression test delivers undrained shear strength in under 15 minutes per specimen, directly to AS 1726.
Service characteristics in Hervey Bay
Demonstration video
Critical ground factors in Hervey Bay
AS 1726-2017 clause 5.3.2 is clear: the unconfined compression test is only valid for saturated cohesive soils that remain undrained during loading. In Hervey Bay, where the water table sits at about 1.5 m depth in the low-lying areas near Urangan, applying UCS results to partially saturated soils can overestimate undrained shear strength by 20 to 30 percent. This is a real risk for slab-on-ground design in the newer developments around Eli Waters. We always check the degree of saturation before running the test and flag samples below 95% saturation for alternative testing methods like the ensayo triaxial with pore pressure measurement.
Our services
Our Hervey Bay lab offers two UCS-related services tailored to local project needs:
Standard UCS on Shelby tube samples
We run the unconfined compression test on 50 mm diameter specimens trimmed from undisturbed tube samples. Reporting includes qu, su, failure strain, moisture content, and stress-strain plot. Turnaround is 2 business days from sample receipt, suitable for preliminary foundation design in Hervey Bay's soft clays.
UCS with post-peak response analysis
For brittle or fissured clays common in the desiccated crust, we continue loading beyond failure to capture the residual strength. This data is critical for slope stability assessments and excavation support designs. We report both peak and residual qu, along with brittleness index (IB).
Frequently asked questions
Which soil types are suitable for the unconfined compression test in Hervey Bay?
The test is suitable for saturated cohesive soils — soft clays, silty clays, and clayey silts — that remain undrained during loading. It is not valid for sands, gravels, or partially saturated soils. In Hervey Bay, the test works well for the Quaternary clays found in the Pialba and Urangan areas.
What is the typical cost range for a UCS test in Hervey Bay?
The typical cost range for a standard unconfined compression test in Hervey Bay is between AU$560 and AU$850 per specimen, including sample preparation, testing, and reporting with stress-strain curves. Volume discounts apply for projects requiring 10 or more specimens.
How does the UCS test differ from a triaxial test?
The UCS test applies axial load only, with no confining pressure, making it faster and simpler than triaxial testing. It provides the undrained shear strength (su) for saturated clays. Triaxial testing adds confining stress to simulate in-situ conditions and can measure drained or undrained strength parameters. For Hervey Bay projects, we often use UCS for preliminary design and triaxial for detailed analysis.
What sample quality is required for reliable UCS results?
AS 1726 requires Class 1 undisturbed samples for UCS testing. In Hervey Bay, we use thin-walled Shelby tubes (50 mm or 75 mm diameter) pushed hydraulically to minimise disturbance. Samples must be sealed immediately to prevent moisture loss and tested within 7 days of collection. Any sample with visible cracks, gas pockets, or excessive disturbance is rejected.