Under AS 1726-2017, the Flat Dilatometer Test (DMT) is a recognised in-situ method for measuring horizontal stress, modulus, and consolidation characteristics in fine-grained soils. In Shepparton, where the Goulburn River floodplain deposits include soft silty clays up to 15 m thick, the DMT provides critical data that SPT or CPT alone cannot capture. The test involves inserting a stainless steel blade with a flexible membrane into the soil and recording the lift-off pressure (p0) and the 1.1 mm deflection pressure (p1). From these, we derive the material index (ID), horizontal stress index (KD), and dilatometer modulus (ED). For projects on river terrace clays, we often combine DMT with calicatas exploratorias to correlate stratigraphy, and with ensayo SPT for strength profiles in deeper sand layers. The result is a high-resolution geotechnical model tailored to Shepparton’s variable ground conditions.
The DMT provides the only direct measure of horizontal stress in Shepparton’s expansive clays, critical for predicting heave and lateral pressure on retaining structures.
Method and coverage
- Material Index (ID): 0.1–3.5 (clay to sand)
- Horizontal Stress Index (KD): 1.5–6.0 (indicating OCR)
- Dilatometer Modulus (ED): 2–50 MPa
- Constrained Modulus (M): derived from ED and ID
Regional considerations
A commercial development on Shepparton’s Numurkah Road encountered 8 m of soft to firm clay overlying dense sand. The initial design assumed uniform settlement, but DMT profiles revealed a 2 m thick layer with KD values below 2.0, indicating underconsolidated clay prone to long-term creep. Without the DMT data, the raft foundation would have experienced differential settlements exceeding 40 mm. We recommended a deep soil mixing program to improve the soft zone. The project proceeded with a hybrid foundation system, saving the client from costly remedial work. This case underscores why DMT is not optional for Shepparton’s floodplain sites.
Standards that apply
AS 1289.6.5.2, AS 1726-2017, AS 4678-2002, NATA ISO/IEC 17025
Complementary services
Standard DMT Sounding
Blade insertion at 0.5 m intervals to 20 m depth. Reports include ID, KD, ED, M, and OCR profiles. Suitable for soft clays, silts, and loose sands.
DMT with Pore Pressure (DMT-P)
Adds pore pressure measurement during dissipation phases. Used to estimate consolidation coefficient (ch) in low-permeability clays typical of Shepparton’s floodplain.
Seismic DMT (SDMT)
Combines DMT with down-hole seismic measurement for vs30/" data-interlink="1">shear wave velocity (Vs). Provides dynamic modulus (G0) for seismic site classification per AS 1170.4.
Typical parameters
Top questions
How does the DMT differ from the CPT in Shepparton’s soils?
The CPT measures cone resistance and sleeve friction continuously, but it does not directly capture horizontal stress or stress history. The DMT provides the horizontal stress index (KD) and dilatometer modulus (ED), which are essential for accurately estimating K0 and OCR in Shepparton’s expansive clays. For soft floodplain deposits, we often run both tests to cross-validate parameters.
What is the typical cost range for a DMT sounding in Shepparton?
A standard DMT sounding to 20 m depth, including full reporting and NATA-calibrated equipment, typically falls between AU$1,370 and AU$1,460. Costs may vary with site access, number of soundings, and required depth. We provide a fixed quote after a site walkover.
Can the DMT be used to assess liquefaction potential?
Yes, but indirectly. The DMT provides the horizontal stress index (KD) and material index (ID), which correlate with relative density and stress state. For liquefaction triggering analysis, we recommend combining DMT with SPT or Vs measurements. The NCEER 2001 method can be adapted using DMT-derived parameters, though it is less common than SPT-based approaches.
How long does a DMT test take on site in Shepparton?
A single 20 m DMT sounding takes approximately 1.5 to 2 hours, including setup, blade insertion, and data download. Multiple soundings on the same site can be completed in one day. We schedule work around Shepparton’s irrigation schedules to avoid saturated ground conditions that could affect blade insertion.