AS 1726 requires site classification based on reliable in-situ measurements, and the Flat Dilatometer Test (DMT) fits that need especially well in Gold Coast. The city's Quaternary sand deposits overlying stiff clay and weathered rock create a layered profile where conventional SPT alone often misses subtle stiffness changes. DMT measures lateral stress, constrained modulus, and undrained shear strength in one push — data that directly feeds foundation design and settlement estimates. Running a DMT alongside a CPT gives us two independent readings of the same soil column, which reduces uncertainty when designing for coastal conditions. Our team runs the test per AS 1289.6.5.2 and cross-references results with local geotechnical databases from previous Gold Coast projects.
DMT captures lateral stress and stiffness at 20 cm intervals — higher resolution than SPT and directly usable for settlement and K0 estimates.
Methodology and scope
Local considerations
A high-rise project in Broadbeach recently relied on DMT results after initial SPT blow counts showed uniform sand across 8 meters. The DMT identified a 2-meter layer of loose, low-stress sand at 3.5 m depth that the SPT had averaged out. That layer would have caused differential settlement under the planned raft foundation. The engineer redesigned the foundation depth based on DMT's KD profile, avoiding a costly rework. This scenario repeats across Gold Coast's coastal strip — DMT catches the thin, low-stiffness layers that SPT and CPT can miss in sands.
Applicable standards
AS 1726:2017 Geotechnical Site Investigations, AS 1289.6.5.2 Standard Test Method for Performing the Flat Plate Dilatometer, FHWA-SA-91-044 Flat Dilatometer Manual (FHWA)
Associated technical services
DMT Sounding Campaign
Full-profile DMT soundings using a 15-tonne CPT rig with dilatometer blade. Continuous 20 cm readings to 30 m depth. Output includes ID, KD, ED, M, su, and K0 profiles delivered in digital format.
DMT Interpretation & Reporting
Data reduction per AS 1289.6.5.2 with correlation to AS 1726 site classes. Includes settlement analysis, K0 estimation, and liquefaction screening for sands. Report includes raw readings, derived parameters, and engineering recommendations.
Typical parameters
Frequently asked questions
What does the Flat Dilatometer Test (DMT) measure in Gold Coast sands?
DMT measures lateral stress, stiffness, and consolidation properties at 20 cm intervals. It provides the horizontal stress index (KD), material index (ID), constrained modulus (M), undrained shear strength (su), and at-rest earth pressure coefficient (K0). These parameters are critical for foundation design in Gold Coast's layered coastal sands.
How does DMT differ from SPT or CPT for site investigation in Gold Coast?
DMT offers higher vertical resolution than SPT (20 cm vs 1.5 m samples) and measures lateral stress directly, which SPT and CPT do not. In Gold Coast's Holocene sands, DMT identifies thin low-stiffness layers that SPT can average out. CPT provides continuous cone resistance but does not measure K0 or dilatometer modulus.
What is the typical cost of a DMT sounding in Gold Coast?
A standard DMT sounding to 20 m depth typically costs between AU$1,340 and AU$1,580, including mobilization within Gold Coast city limits. The rate varies with depth, site access, and number of soundings. Contact our lab for a quote tailored to your project scope.
Which Gold Coast soil conditions are best suited for DMT testing?
DMT performs best in sands, silts, and low-plasticity clays — exactly the materials found across Gold Coast's coastal plain and floodplain deposits. It is less effective in gravels or very stiff clays where the blade cannot penetrate. For those conditions, we recommend CPT or SPT as alternatives.