In Geelong, the subsurface conditions vary significantly between the volcanic plains north of the Barwon River and the Quaternary alluvium along the coast. The Flat Dilatometer Test (DMT) offers a fast, repeatable way to measure in-situ horizontal stress, modulus, and soil behaviour type. We follow AS 1726-2017 for site investigation and AS 1289.6.5.2 for the DMT procedure. For deep foundations in soft clays, we often combine DMT with ensayo SPT to cross-check strength profiles. The test is particularly useful in Geelong's stiff basaltic clays, where conventional sampling disturbs the fabric.
The DMT gives us three independent parameters per reading – material index, horizontal stress, and modulus – all from one push.
Scope of work in Geelong
Typical technical challenges in Geelong
Geelong sits on the Otway Basin, with known tectonic activity from the Torquay fault zone. The last significant earthquake (magnitude 5.5) in 2012 near Moe caused minor damage, but the probability of a larger event in the region is non‑negligible. For sites in the Newtown or Belmont suburbs underlain by soft estuarine clays, a DMT profile is essential to identify layers with high compressibility and low lateral stress. Ignoring these can lead to differential settlement exceeding 50 mm in a 10‑storey building.
Our services
We offer two tailored DMT service levels to match project budget and complexity:
Standard DMT Sounding
Single‑point readings every 200 mm to a maximum depth of 30 m. Includes raw data, ID/KD/ED profiles, and a brief interpretation report. Suitable for preliminary design and subgrade classification.
Advanced DMT with Seismic Module
Adds shear‑wave velocity (Vs) measurement at 1‑m intervals using a geophone embedded in the blade. Provides G0 and small‑strain stiffness. Ideal for dynamic analyses and settlement verification in Geelong's soft zones.
Frequently asked questions
How does the DMT differ from the CPT in Geelong clays?
The DMT measures horizontal stress and stiffness directly, while the CPT gives cone resistance and pore pressure. In stiff basaltic clays of Geelong, the DMT often shows a higher sensitivity to fabric changes than the CPT. We typically use both when a detailed stiffness profile is needed.
What is the typical cost of a DMT investigation in Geelong?
The range for a standard DMT project in Geelong is AU$1,450 to AU$1,760. This includes mobilisation within 20 km of the city centre, five DMT pushes to 15 m depth, and a basic report. Volume discounts apply for multi‑location surveys.
Can the DMT be used to assess liquefaction potential?
Yes, but indirectly. The DMT provides KD and ED, which correlate with cyclic resistance ratio (CRR) through Marchetti & Monaco (2005) relationships. For a full liquefaction assessment, we combine DMT with SPT or Vs data. In Geelong's sandy layers near the Barwon River, this combination gives reliable triggering curves.
What depth can the DMT reach in Geelong's volcanic soils?
In stiff basaltic clays and weathered basalt, the DMT typically reaches 25–30 m with a 20‑tonne CPT truck. In very dense layers, refusal may occur earlier. We pre‑drill through hard crusts using a rotary tool to avoid blade damage. Maximum depth in soft alluvium exceeds 40 m.