Ballarat's 19th-century gold rush drove rapid urban expansion over deep alluvial terraces and swampy flats. Many of the older suburbs were built on soft clays and silts left by ancient lake systems, which still cause differential settlement in heritage structures today. That's why we rely on the Flat Dilatometer Test (DMT) here more than in many other Victorian cities. It gives us precise horizontal stress and modulus data without the disturbance of a borehole. Before we design a footing for a Ballarat home, we often run a DMT alongside a calicata exploratoria to correlate stratigraphy with mechanical response. The test is fast — about 20 minutes per push — and yields reliable parameters for both shallow and deep foundations.
The DMT yields horizontal stress and modulus data without borehole disturbance — critical for Ballarat's soft lacustrine clays.
Technical details of the service in Ballarat
- Material Index (ID) for soil classification
- Horizontal Stress Index (KD) to estimate overconsolidation ratio
- Dilatometer Modulus (ED) for immediate settlement calculations
Typical technical challenges in Ballarat
Ballarat sits on the margin of the Otway Basin, where Cenozoic sediments overlie Paleozoic basement. The shallow water table — often within 2-3 m of the surface in low-lying areas — means that even a moderate rain event can saturate soft clays and trigger differential movement. The DMT's ability to detect overconsolidation from past desiccation or loading helps us identify zones prone to collapse or heave. We've seen cases where ignoring the lateral stress history led to cracked slabs within two years. For projects near the Yarrowee River floodplain, we always push the blade to at least 6 m to map the soft layer thickness.
Our services
We offer two complementary DMT-based services tailored to Ballarat's ground conditions:
DMT Seismic Profiling (SDMT)
Adds shear wave velocity measurement to the standard DMT push, giving VS profiles for site class assessment per AS/NZS 1170. Essential for seismic response analysis in Ballarat's moderate seismicity zone.
DMT for Settlement Design
Focused on immediate and consolidation settlement estimates using ED and constrained modulus (M). We provide a report with settlement contours for footing pads, rafts, and slabs.
Frequently asked questions
How does the DMT differ from the CPT in Ballarat soils?
The CPT measures cone resistance and sleeve friction, while the DMT measures horizontal stress and modulus directly. In Ballarat's soft lacustrine clays, the DMT's membrane displacement gives a more sensitive reading of overconsolidation and stiffness at low stress levels. We often use both: CPT for stratigraphy, DMT for deformation parameters.
What is the typical cost of a DMT in Ballarat?
A standard DMT sounding to 10 m depth ranges between AU$1.430 and AU$1.860, including mobilisation within the Ballarat urban area. Deeper pushes or seismic add-ons increase the price. Contact us for a firm quote based on your specific site and access conditions.
Can the DMT be used for liquefaction assessment?
Indirectly, yes. The DMT's KD index correlates well with cyclic resistance ratio (CRR) using the method by Robertson (2010). For Ballarat sites with loose saturated sands — rare but possible near old creek channels — we combine DMT with SPT to get both KD and N-values for a solid liquefaction evaluation.
What depth can the DMT reach in Ballarat's stiff basalt clays?
In residual basaltic clays over Mount Clear or Buninyong, the blade typically reaches 8-12 m before refusal. In the softer alluvial fills near the city centre, we've pushed to 25 m. The limiting factor is the thrust capacity of the rig — we use a 20-tonne CPT truck for deep profiles.