Many industrial sites in Mackay show premature cracking in rigid pavements because the subgrade evaluation stopped at a standard CBR. The local geology, dominated by alluvial clays and tidal flat deposits near the Pioneer River, demands a deeper assessment of subgrade reaction modulus (k-value). Without a site-specific k-value, a 200 mm slab on a soft clay can lose 40% of its structural capacity. We combine plate load tests, ensayo CBR vial for soaked and unsoaked conditions, and undisturbed sampling to calibrate the modulus. This avoids the common error of using generic Austroads tables for a site where groundwater sits 1.2 m below formation level.
A rigid pavement on Mackay alluvial clay without a site-specific k-value can lose 40% of its structural capacity within five years.
Methodology and scope
A typical distribution centre in Paget, Mackay, with a 250 mm jointed reinforced concrete pavement requires two critical inputs: the design CBR and the elastic modulus of the subgrade. We run repeated plate load tests (AS 1289) on the prepared subgrade to derive the modulus of subgrade reaction. The process follows this sequence:
In-situ CBR at 95% of standard Proctor density (AS 1289.6.1.1)
Plate load test with 300 mm and 762 mm plates to compute k-value ratio
Triaxial modulus testing on recompacted samples for fatigue analysis
When the subgrade shows high plasticity (PI > 30), we incorporate suelos expansivos modelling to check for differential movement at joints. For heavy-duty pavements in fuel terminals, we cross-check the slab thickness with capacidad de carga analysis of the underlying foundation layer. The goal is to limit edge stress below 1.8 MPa for 40 MPa concrete under 10⁶ load repetitions.
Technical reference image — Mackay
Local considerations
Mackay sits in a region with a shallow water table, often 0.5–1.5 m below surface after the wet season. If the rigid pavement design ignores the effect of moisture on subgrade modulus, the slab loses support under the outer wheel path. The result is corner cracking starting at the second year of service. We require drainage trials and permeabilidad campo testing to size edge drains. Where the subgrade is compressible (CBR < 3%), we evaluate the need for a cement-treated sub-base or geogrid reinforcement below the slab. The design must also account for the cyclic loading from cane trucks on local haul roads, which induce tensile stresses 30% higher than standard highway traffic.
Field and laboratory CBR at OMC, soaked and unsoaked, plus dynamic cone penetrometer profiles for uniformity across the pavement footprint.
02
Modulus of Subgrade Reaction (k-value)
Plate load tests with 300 mm and 762 mm plates on prepared subgrade, reported as a design k-value with correction for slab size.
03
Concrete Mix Design Review
Verification of flexural strength, shrinkage, and coefficient of thermal expansion to match the joint spacing and climate of Mackay.
04
Pavement Structural Analysis
Finite element modelling of slab stresses under axle loads, including dowel bar transfer and edge support from curbs or tied shoulders.
Applicable standards
Austroads Guide to Pavement Technology Part 2 (2017), AS 1726:2017 – Geotechnical site investigations, AS 4678:2002 – Earth retaining structures (interface with pavement), AS 1289 – Standard test method for nonrepetitive static plate load tests
Frequently asked questions
What CBR value is typical for rigid pavement subgrades in Mackay?
For natural subgrade in Mackay, the soaked CBR ranges from 2% to 7% depending on the clay content and moisture. After lime or cement stabilisation, it can reach 15–25%, which significantly reduces the required slab thickness.
How much does rigid pavement design service cost in Mackay?
The cost for a full rigid pavement design package, including subgrade testing, k-value derivation, and structural analysis, ranges between AU$2,860 and AU$10,100 depending on the pavement area and testing density. Final pricing is confirmed after site inspection.
Do you follow Austroads or AASHTO for joint spacing in Mackay pavements?
We follow Austroads Guide Part 2 (2017) as the primary reference, with AASHTO empirical checks for heavy-traffic industrial pavements. Joint spacing is calculated from slab length-to-thickness ratio, concrete flexural strength, and subgrade restraint, typically 4.5–6.0 m for Mackay conditions.
