Our team brings a calibrated hydraulic jack and a set of steel plates ranging from 300 to 762 mm in diameter directly to your site in Mackay. We position the reaction frame against a loaded truck or anchored beams, then apply load increments while monitoring settlement with precision dial gauges. Each plate load test follows the procedures of AS 1726 for in-situ stiffness evaluation. The data we collect lets us calculate the modulus of subgrade reaction (k-value) and ultimate bearing capacity for spread footings, raft slabs, or pavement layers. For sites with shallow water table, we also incorporate asentamiento diferencialanalysis to understand uneven movement risks.
A plate load test directly measures how the ground will deform under real footing pressures, not a laboratory estimate.
Methodology and scope
Mackay sits on Quaternary alluvial deposits and coastal sands, where soil stiffness varies widely within short distances — a 5 m change in location can double the modulus. That is why we perform plate load tests at multiple points, not just one. The test itself follows a standard sequence:
Seat the plate on a thin layer of fine sand or plaster to ensure uniform contact.
Apply load in eight equal increments up to 1.5 times the design pressure.
Hold each increment until settlement stabilises (typically 5-10 min).
We record the load-settlement curve and derive the modulus of subgrade reaction, which feeds directly into foundation design. To complement these results, we often cross-reference with ensayo triaxial for shear strength parameters, and with consolidacion data when clay layers underlie the test depth. The combination of PLT and lab tests gives a complete picture of the subgrade behaviour.
Technical reference image — Mackay
Local considerations
Mackay's coastal geology includes soft estuarine clays and loose sands near the Pioneer River. These materials can show high compressibility and low bearing capacity, especially after heavy rain when the water table rises within a metre of the surface. A foundation designed without a plate load test may assume uniform stiffness that does not exist. The real risk is not just total settlement but differential settlement between adjacent footings, which cracks slabs and misaligns structures. We have seen cases where a single PLT at the right depth revealed a 40% drop in subgrade modulus compared to the assumed design value, forcing a redesign of the footing size before concrete was poured.
Settlement at each load increment, rebound settlement
Derived values
Modulus of subgrade reaction (k), modulus of elasticity (E)
Test duration per point
2 to 4 hours including setup
Applicable standard
AS 1726 – Geotechnical site investigations
Associated technical services
01
Static plate load test (non-repetitive)
Standard single-cycle load test for bearing capacity and modulus of subgrade reaction. Ideal for shallow foundations, crane pads, and pavement subgrades. Load applied in equal increments to 1.5 times design pressure.
02
Cyclic plate load test
Repeat loading-unloading cycles to simulate traffic or machinery vibrations. Used for heavy industrial slabs, port pavements, and rail subballast. Provides resilient modulus and permanent deformation behaviour.
Applicable standards
AS 1726 – Geotechnical site investigations, AS 1289 – Standard test method for nonrepetitive static plate load tests, AS 4678 – Earth-retaining structures (reference for design parameters)
Frequently asked questions
How deep does the plate load test represent the soil profile?
The test influences soil to a depth of about 1.5 to 2 times the plate diameter. For a 450 mm plate, that is roughly 0.7 to 0.9 m. If your foundation sits deeper, we can perform the test at that depth in a test pit or use a larger plate to increase the zone of influence.
What is the difference between plate load test modulus and laboratory modulus?
The plate load test gives an in-situ modulus that reflects the actual soil fabric, moisture content, and stress history. Laboratory tests on undisturbed samples often give higher values because sampling disturbs the soil structure. For design, the in-situ modulus from PLT is more reliable for immediate settlement calculations.
How much does a plate load test cost in Mackay?
The typical cost ranges between AU$1,310 and AU$2,190 per test point, including mobilisation within the Mackay region. Final pricing depends on the plate size, number of test points, and site access conditions. We provide a fixed quote after a quick site review.
