Mackay sits on the floodplain of the Pioneer River, where Quaternary alluvium up to 40 m deep overlays the bedrock. These saturated, loose to medium-dense sands and soft clays make the Flat Dilatometer Test (DMT) a logical first step for foundation design in Mackay. The DMT delivers the in-situ horizontal stress index and modulus with minimal disturbance, data that standard SPT cannot replicate in these compressible layers. Our team runs the test to AS 1289.6.1.1 and supplements it with ensayo CPT when continuous stratigraphic profiling is required.
The DMT’s horizontal stress index is the single most reliable predictor of lateral earth pressure in Mackay’s overconsolidated clays.
Methodology and scope
A common mistake contractors make in Mackay is relying solely on SPT N-values to estimate settlement in the soft estuarine clays of the Bakers Creek area. These clays often show low N-values but moderate strength — the DMT picks up the difference. We deploy the flat blade using standard CPT rigs, recording every 200 mm. The test yields three key parameters: material index (ID), horizontal stress index (KD), and dilatometer modulus (ED). All data is processed in real time and cross-checked against Casagrande’s soil classification framework. For projects requiring undrained shear strength profiles, we combine DMT with veleta-campo to validate the correlation.
Technical reference image — Mackay
Local considerations
The DMT blade is 95 mm wide and 15 mm thick, inserted hydraulically at 20 mm/s. In Mackay’s gravelly lenses near the river mouth, the membrane risks rupture if the push rate exceeds 25 mm/s. We monitor penetration resistance continuously and adjust the inflation sequence. A torn membrane voids the test and wastes a shift. Our crews carry spare membranes and calibrate the gauge against a dead-weight tester before each deployment. The real risk is misinterpreting KD in the cemented layers of the Andromache River terrace, where the index can double without a corresponding strength gain.
Full-depth soundings with 200 mm intervals in sands, silts, and clays. Real-time data acquisition and on-site preliminary interpretation.
02
Seismic DMT (SDMT)
Combines vs30/" data-interlink="1">shear wave velocity measurement with DMT readings. Ideal for site class determination under AS 1170.4 in Mackay’s soft soil zones.
03
Pore Pressure DMT (PDMT)
Dissipation tests to estimate in-situ coefficient of consolidation. Critical for settlement analysis in the North Mackay industrial precinct.
04
DMT for Deep Foundations
Direct measurement of lateral earth pressure for drilled shaft design. Used in the Harbour Road bridge project to verify shaft capacity.
Applicable standards
AS 1289.6.1.1 – Determination of the DMT index, AS 1289.6.5.2 – Standard Test Method for Performing the Flat Plate Dilatometer, FHWA-RD-97-022 – DMT calibration guidelines
Frequently asked questions
How does the DMT compare to SPT in Mackay's soils?
The DMT provides continuous profiles of horizontal stress and modulus, unlike the SPT which gives discrete blow counts. In the soft clays of the Pioneer River floodplain, the DMT detects thin sand lenses that SPT often misses. It also yields a reliable overconsolidation ratio, which is critical for settlement estimates.
What is the typical cost range for a DMT in Mackay?
A standard DMT sounding in Mackay costs between AU$1,450 and AU$1,540 per 10 m depth, including mobilization and a preliminary report. Additional costs apply for seismic or pore pressure modules. Prices reduce slightly for multiple soundings in the same zone.
How deep can the DMT penetrate in Mackay's alluvial soils?
We routinely reach 25 m in the loose sands and soft clays of the northern suburbs. In the cemented gravels near the city center, refusal occurs around 15 m. The limiting factor is the thrust capacity of the CPT rig, not the blade itself.
