For geotechnical and civil projects in Mackay, infiltration testing is a critical component under AS 1726. The city's high seasonal rainfall — averaging over 1600 mm annually — combined with its coastal alluvial and residual clay soils demands precise field measurements of hydraulic conductivity. We perform double-ring infiltrometer tests according to AS 1289 and Porchet tests per local standards to determine true infiltration rates. This data directly informs the design of soakwells, stormwater detention systems, and subsurface drainage. Before undertaking any large-scale earthworks in Mackay, a reliable permeability field test ensures the proposed infiltration rates are not overestimated, preventing surface ponding or groundwater mounding issues.
Double-ring infiltrometer testing in Mackay's clayey sands reduces Ksat overestimation by up to 40% compared to single-ring methods, avoiding undersized drainage systems.
Methodology and scope
Mackay's urban expansion over the past two decades has pushed development into areas underlain by the Mackay Formation — a sequence of clayey sands, silts, and marine muds with highly variable permeability. Our infiltration testing protocol adapts to these conditions: we first classify soil texture using field hand-sorting and hydrometer analysis, then select either the Porchet (single-ring constant head) or double-ring infiltrometer method. The double-ring setup isolates vertical flow, giving accurate Ksat values even in layered profiles. For sites near the Pioneer River or coastal lowlands, we couple the infiltration test with a drainage geotechnical survey to evaluate lateral groundwater flow paths. All field data is reduced using the Philip or Green-Ampt models to produce design infiltration rates.
Technical reference image — Mackay
Local considerations
In Mackay, many times we see designs that assume uniform infiltration across a site when in fact the clay lenses in the Mackay Formation create anisotropic conditions. A single ring test can miss these horizontal barriers, leading to soakwell failure within the first wet season. The real risk is not just surface ponding — it's the development of a perched water table that saturates foundation subgrades and triggers differential movement in slabs. Using the double-ring infiltrometer method, we identify these low-permeability layers and recommend targeted drainage measures or increased soakwell depths. This approach has proven essential in the Glenella and Mount Pleasant suburbs.
Inner 300 mm, outer 600 mm (double); 300 mm (Porchet)
Test depth
0.3 m to 2.0 m below ground surface
Duration per test
2–6 hours depending on soil permeability
Reporting standard
AS 1726-2017, AS/NZS 1547:2012
Associated technical services
01
Double-ring infiltrometer testing
Standard AS 1289 method with inner/outer ring setup for accurate saturated hydraulic conductivity in clayey sands and silts. Includes constant-head water supply and timed readings until steady-state flow is achieved.
02
Porchet (single-ring) testing
Constant-head single-ring method suitable for preliminary assessments or sites with uniform sandy soils. Faster execution — typically 2 hours per test — but less accurate in layered profiles.
03
Infiltration rate analysis & reporting
Field data reduced using Philip and Green-Ampt infiltration models. Report includes Ksat values, design infiltration rates, and recommendations for soakwell sizing per AS/NZS 1547.
04
Permeability profiling
Combination of double-ring tests at multiple depths to identify low-permeability clay lenses. Coupled with soil classification and moisture content profiles for comprehensive drainage design input.
Applicable standards
AS 1726-2017 Geotechnical site investigations, AS 1289.6.8.1 Standard test method for infiltration rate of soils in field using double-ring infiltrometer, AS/NZS 1547:2012 On-site domestic wastewater management, AS 4678-2002 Earth retaining structures (referenced for drainage design)
Frequently asked questions
What is the difference between a double-ring and single-ring infiltration test?
The double-ring infiltrometer uses an outer guard ring to force vertical flow in the inner ring, giving a more accurate measure of saturated hydraulic conductivity (Ksat) in layered soils typical of Mackay's alluvial profiles. The single-ring (Porchet) method allows lateral flow, which overestimates infiltration rates by up to 40% in clayey sands. For soakwell design in subdivisions, we recommend double-ring testing.
How much does an infiltration test cost in Mackay?
A standard double-ring infiltrometer test including field work and reporting typically ranges between AU$560 and AU$640 per test point. Volume discounts apply for developments requiring 6 or more test locations. The price includes setup, water supply, 4–6 hours of field monitoring, and a certified report with design infiltration rates.
When should I conduct infiltration testing for a Mackay development?
Infiltration testing should be done after the site has been cleared and rough-graded, but before final engineering design. In Mackay, the best period is during the dry season (May to October) when the water table is lowest and soil moisture is at field capacity — this yields the most conservative design rates. For council approvals, tests must be performed within 12 months of the application date.
