Melbourne's geology is a geotechnical mosaic — from the stiff Yarra River clay terraces to the loose Quaternary sands of the Port Phillip coastline. The Flat Dilatometer Test (DMT) shines precisely in these conditions because it captures lateral stress and deformation modulus at every 20 cm depth increment, something a standard SPT log alone cannot do. We have deployed the DMT across over 60 sites in Melbourne, from Southbank high-rises to Cranbourne residential subdivisions, and the pattern is consistent: the city's variable alluvium demands a test that reads both strength and stiffness in the same push. Before mobilising the blade, we often pair the DMT with a resistivity survey to map stratigraphic boundaries, ensuring we target the critical layers. The blade itself is a stainless steel wedge with an expandable membrane — it measures the pressure needed to lift the membrane (p0), then the pressure at 1.1 mm expansion (p1). From those two numbers we derive the material index (Id), horizontal stress index (Kd), and dilatometer modulus (Ed). For Melbourne's deeply weathered Silurian mudstone profiles, the DMT's ability to detect overconsolidation ratios above 4 is particularly valuable — it tells us whether the ground has been preloaded by past glaciation or simply deposited under normal conditions.
The DMT gives us both stiffness and stress history in one push — for Melbourne's variable alluvium, it halves the uncertainty in settlement predictions.