A two-storey residential development in the inner-south suburb of Unley ran into trouble when standard strip footings failed to meet the required edge heave parameters during a pre-pour inspection. The site sat on a pocket of moderately reactive Keswick Clay, and the only viable solution was a structural stiffened raft designed to AS 2870. Our laboratory ran Atterberg limits and shrink-swell index testing on Shelby tube samples to provide the site classification data the structural engineer needed. This is where raft/mat foundation design in Adelaide moves beyond generic slab detailing and into the realm of soil-structure interaction. We correlate borehole logs with laboratory consolidation curves so the raft geometry and beam depth reflect the actual moisture variation profile across the Adelaide Plains, whether the project sits on the Hallett Cove sandstone transition or the deep alluvium of the River Torrens corridor. When the geotechnical profile gets complicated, we often pair the investigation with triaxial testing to define the drained strength parameters for finite element modeling, or use in-situ permeability data to calibrate the long-term suction predictions under the slab.
In Adelaide, the difference between a Class M and Class H1-D site often comes down to 15 mm of predicted ground movement—something only a full shrink-swell test suite can resolve.
