Coffs Harbour sits on a mix of coastal sands and residual clay soils derived from the Paleozoic metasediments of the Great Dividing Range. The shallow water table near the beachfront adds complexity to rigid pavement design. We assess subgrade reactivity, drainage conditions, and traffic loads to define slab thickness and joint spacing. Before finalising the design, we often run a resistivity survey to map soil variability across the site, and a dilatometer test to obtain the in-situ modulus of subgrade reaction. This local data ensures the pavement resists curling and fatigue cracking under Coffs Harbour's subtropical rainfall.
The shallow water table near Coffs Harbour beachfront adds complexity to rigid pavement design, requiring careful subgrade drainage assessment.
Method and coverage
A recent warehouse project on the industrial estate off Hogbin Drive required a rigid pavement for heavy forklift traffic. The subgrade was a stiff clay with low permeability. We designed a 200 mm jointed reinforced slab with dowelled contraction joints every 5 m. The design followed the 1992 AUSTROADS Pavement Design Guide and AS 1726 for site investigation. We verified the subgrade modulus with plate load tests (Austroads method) and used the Westergaard edge-loading equations to check corner stresses. A losa de cimentacion approach was considered for the adjoining building slab, but the rigid pavement stood alone. Key outputs:
Slab thickness: 200 mm
Joint spacing: 5.0 m
Concrete flexural strength: 4.5 MPa at 28 days
Subgrade reaction modulus (k): 35 MPa/m
Technical reference image — Coffs Harbour
Regional considerations
Coffs Harbour receives over 1,600 mm of rain annually, with intense east-coast lows. Poor subgrade drainage under a rigid pavement can lead to pumping at joints, loss of support, and slab corner cracking. We have seen premature failures in local streets where the subgrade was not treated. Our designs include a 150 mm granular subbase with a minimum CBR of 15% and a geotextile separator where the clay is active. We also require a 1% crossfall and edge drains to intercept lateral flow. Skipping these steps raises the risk of slab faulting and ride quality loss within 5 years.
Boreholes, DCP tests, and laboratory CBR to characterise support conditions across the site.
02
Pavement Structural Design
Slab thickness, joint layout, steel reinforcement, and concrete specification per AUSTROADS and AS 3600.
03
Drainage Design
Subbase drainage layer, edge drains, and crossfall analysis to prevent water entrapment.
04
Construction Quality Assurance
Inspection of subgrade preparation, concrete placement, joint cutting, and curing.
Standards that apply
AS 1726:2017 Geotechnical site investigations, AUSTROADS Pavement Design Guide (1992 or later), AS 3600:2018 Concrete structures, AS 4678:2002 Earth-retaining structures (if integral kerbs)
Top questions
How does the subgrade type in Coffs Harbour affect rigid pavement design?
The coastal sands have high permeability but low bearing capacity, while the residual clays are stiff but shrink-swell reactive. Both require different subbase thickness and drainage. We test the subgrade modulus (k) on site to tailor the design.
What design code do you follow for rigid pavements in Coffs Harbour?
We apply the AUSTROADS Pavement Design Guide and AS 1726 for site investigation. Concrete design follows AS 3600. For heavy industrial loads, we also reference the Portland Cement Association method.
What is the typical cost range for a rigid pavement design study in Coffs Harbour?
The cost typically ranges between AU$2,770 and AU$10,770, depending on site size, number of boreholes, laboratory tests, and design complexity. Contact us for a specific quote.
Do you consider joint spacing and load transfer in your designs?
Yes. We calculate joint spacing based on slab thickness, concrete strength, and subgrade friction. Dowel bars are specified at contraction joints for heavy traffic to transfer load and prevent faulting.
