Our field team deploys the Marchetti dilatometer blade — a 95 mm wide stainless steel probe — directly into the ground via a hydraulic penetrometer rig. In Bendigo, where the subsurface transitions from gold-bearing quartz reefs to stiff alluvial clays along the Campaspe River, the DMT provides key parameters: horizontal stress index (K_D), material index (I_D), and dilatometer modulus (E_D). We push the blade at a constant 20 mm/s rate, pausing every 200 mm to inflate the membrane and record the A and B pressures. This method yields continuous profiles without soil removal, ideal for sites where historical mining activity or variable fill layers require careful stiffness characterisation. Before testing, we review borehole logs from nearby Council records to target depth intervals with known heterogeneity. The resulting data feeds directly into settlement calculations for slab-on-grade and footing designs across residential subdivisions in Bendigo's growth corridors. We complement this with a geotechnical resistivity survey to map subsurface anomalies before DMT deployment, ensuring the probe avoids buried debris.
The DMT delivers in-situ horizontal stress and modulus data with a resolution unmatched by standard SPT or laboratory triaxial tests on disturbed samples.
Methodology and scope
Bendigo sits on the Box Creek Fault system, with sedimentary sequences that vary laterally within short distances. This makes the DMT particularly valuable for measuring the constrained modulus (M_DMT) and coefficient of earth pressure at rest (K_0). The test follows AS 1289.6.5.2 and Australian standard AS 1726-2017 for site investigation. Key outputs include:
Material index (I_D) for soil classification — clay, silt or sand
Horizontal stress index (K_D) for OCR estimation
Dilatometer modulus (E_D) for immediate settlement analysis
K_0 values for retaining wall design and excavation support
We typically complete 30 to 50 test points per project in Bendigo, spaced 5–8 m apart along alignment corridors. The equipment is calibrated weekly against a NATA-traceable load cell. For projects requiring shear strength profiles at depth, we cross-reference DMT results with cone penetration tests to validate soil behaviour type boundaries. The combined dataset reduces uncertainty in bearing capacity estimates by roughly 15–20 percent compared to SPT-only approaches.
Technical reference image — Bendigo
Local considerations
Ignoring the DMT in Bendigo can lead to underestimating foundation settlements on the stiff to hard clays that dominate the eastern suburbs. The local geology includes the Bendigo Goldfield's folded Ordovician turbidites, where weathered rock zones sit directly beneath thin soil covers. Without a dilatometer test, designers may overestimate bearing capacity by assuming uniform stiffness values. AS 4678-2002 for earth retaining structures and AS/NZS 1170.4 for seismic actions require site-specific modulus profiles for serviceability checks. The K_0 values measured by DMT directly affect lateral earth pressure calculations for basement walls and shoring systems. In areas with historical underground workings, the DMT's ability to detect soft zones at depth is critical — a standard borehole may miss a metre-thick void. We always pair DMT soundings with MASW surveys to cross-check vs30/" data-interlink="1">shear wave velocity profiles, particularly when seismic site class influences foundation design.
Continuous profiling at 200 mm intervals to 15 m depth. Includes A and B pressure readings, material index, horizontal stress index, and constrained modulus. Delivered as a PDF report with depth plots and interpreted soil behavior type chart.
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DMT with Dissipation Testing
Adds pore pressure dissipation tests at selected depths to estimate coefficient of consolidation (c_h). Essential for soft clay layers in Bendigo's low-lying areas where long-term settlement governs pavement design.
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DMT for Retaining Wall Design
Extended profiling to 25 m with K_0 determinations at 1 m intervals. Includes lateral earth pressure coefficients at rest and at failure, directly input for AS 4678-2002 wall design. Recommended for deep excavations near Bendigo's heritage buildings.
Applicable standards
AS 1289.6.5.2: Standard Test Method for Performing the Flat Plate Dilatometer, AS 1726-2017: Geotechnical Site Investigations, AS 4678-2002: Earth Retaining Structures, AS/NZS 1170.4: Structural Design Actions – Earthquake
Frequently asked questions
How does the DMT differ from the CPT in Bendigo's soils?
The DMT measures horizontal stress and modulus directly, while the CPT provides cone resistance and friction sleeve data. In Bendigo's stiff clays, the DMT gives more reliable K_0 and settlement parameters. For profiling thin sand layers interbedded with clays, the CPT's higher vertical resolution is preferable. We often combine both tests on critical projects.
What is the typical cost range for a Flat Dilatometer Test in Bendigo?
For a standard DMT profile to 15 m depth with 30 test points, the cost ranges between AU$1.450 and AU$1.430, including mobilisation within the Bendigo urban area. Dissipation testing adds approximately AU$180 per test. Volume discounts apply for multi-lot subdivisions or repeat projects.
Can the DMT detect old mine workings beneath Bendigo?
Yes, indirectly. The DMT measures soil stiffness and stress state; a sudden drop in modulus (E_D) or a shift in material index (I_D) at depth can indicate a filled or open void. However, the DMT blade is not a void-finder. We recommend pairing it with georadar or MASW surveys to confirm anomalies before drilling confirmation boreholes.
What depth can the DMT reach in Bendigo's ground conditions?
In typical Bendigo soils — stiff clays and weathered siltstone — the DMT can reach 25–30 m with a 10-tonne cone penetrometer truck. Harder layers like quartz reefs or fresh sandstone may stop the blade at shallower depths. We review existing borehole logs to estimate refusal depth before mobilisation and adjust the test plan accordingly.
