A mid-rise development on Collins Street recently uncovered a layer of soft estuarine clay at 6 m depth, right where the footing zone was planned. Without a proper bearing capacity analysis, that building would have settled unevenly within months. Hobart sits on a mix of dolerite bedrock, alluvial sands, and marine clays deposited during past glacial periods. The city's landscape demands site-specific investigation because soil profiles change abruptly between the CBD and the suburbs. We combine fieldwork with laboratory testing to deliver reliable bearing capacity values for any project. Before construction, we often perform a plate load test on site to validate our calculations against real ground response.
Hobart's dolerite bedrock offers high bearing capacity, but soft alluvial clays in the Derwent estuary can drop values below 100 kPa.
Methodology and scope
- In-situ testing with SPT and CPT to measure penetration resistance
- Laboratory triaxial and consolidation tests on undisturbed samples
- Empirical correlations from local databases calibrated to Hobart soils
Local considerations
AS 4678 clause 4.3.2 requires bearing capacity analysis to account for both ultimate limit state and serviceability limit state. In Hobart, the main risk is not the dolerite — it is the hidden pockets of soft clay or loose sand left behind by ancient river channels. A site may test fine at one corner but fail at another. Without thorough investigation, differential settlement can crack walls and tilt floors. We always cross‑check field data with laboratory consolidation curves to catch these weak zones before the foundation is poured.
Applicable standards
AS 1726 – Geotechnical Site Investigations, AS 4678 – Earth Retaining Structures, AS/NZS 1170 – Structural Design Actions
Associated technical services
Shallow Foundation Bearing Capacity
For spread footings, strip footings, and slabs on grade. We calculate ultimate and allowable bearing capacity using Terzaghi, Meyerhof, and Hansen methods. Field tests include plate load tests and SPT. Laboratory tests cover triaxial, direct shear, and consolidation. Suitable for residential, commercial, and industrial structures up to 5 storeys.
Deep Foundation Bearing Capacity
For piles, piers, and drilled shafts in Hobart's variable soils. We evaluate end‑bearing and skin friction from SPT, CPT, and laboratory strength tests. We also perform dynamic pile testing and static load tests when required. Suitable for high‑rise buildings, bridges, and infrastructure projects where shallow soils are inadequate.
Typical parameters
Frequently asked questions
What is the typical bearing capacity of Hobart soils?
It varies widely. Weathered dolerite in areas like Sandy Bay can support 500–800 kPa for shallow foundations. Soft alluvial clays in Moonah or the Derwent estuary may only provide 100–150 kPa. Our analysis always accounts for local conditions.
How much does a bearing capacity analysis cost in Hobart?
The typical range for a residential site is AU$830 to AU$2,890, depending on the number of test pits, SPT holes, and laboratory tests. Larger commercial projects may cost more due to deeper borings and advanced triaxial testing. Contact us for a tailored quote.
What is the difference between ultimate and allowable bearing capacity?
Ultimate bearing capacity (qu) is the maximum pressure the soil can support before failure. Allowable bearing capacity (qa) is qu divided by a factor of safety (usually 2.5 to 3.0). We always report both values so the structural engineer can design with the appropriate safety margin.