We have worked on several rural road upgrades around Shepparton where the underlying clay soils were too plastic to support pavement loads without treatment. One project along the Goulburn Valley Highway required stabilising a 2.5 km stretch of active floodplain clay with a plasticity index above 40. We designed a lime-cement blend at 4% by dry weight, achieving a 7-day UCS gain from 0.8 MPa to 2.3 MPa. Before prescribing the mix, we first ran a full classification of the soil to determine clay mineralogy and then correlated the results with CBR vial soak values to set the design subgrade modulus.
In Shepparton's alluvial clays, a plasticity index above 35 almost always requires chemical stabilisation before the pavement can achieve design life.
Method and coverage
Regional considerations
The main geotechnical risk in Shepparton is the high shrink-swell potential of the Goulburn Valley clays. Without proper soil stabilisation for roads, the pavement will crack longitudinally and develop differential settlement at bridge approaches. AS 4678-2002 requires a minimum soaked CBR of 5% for subgrades under flexible pavements, but many natural soils here fail at 1–2%. If the stabilisation depth is underestimated or the lime content is too low, the road may show rutting within two years. We always run a full suite of index tests plus a trial compaction strip to verify the design mix before bulk placement.
Standards that apply
AS 1726-2017 Geotechnical site investigations, AS 4678-2002 Earth-retaining structures (applied to cut slopes), Austroads Guide to Pavement Technology Part 2: Pavement Structural Design (2017)
Complementary services
Lime Stabilisation
Application of quicklime (CaO) or hydrated lime to reduce plasticity and increase workability. We design the dosage based on the Eades & Grim test (AS 1289) and verify with pH measurements at 1-hour and 24-hour intervals. Typical dosage for Shepparton clays is 3–5%.
Cement Stabilisation
Portland cement mixed at 3–7% by dry mass for faster strength gain. Suitable for low-PI clays and silty sands. We perform unconfined compression tests at 7 and 28 days and correlate with CBR to validate the design modulus. Used when construction schedules are tight.
Mechanical Stabilisation with Geogrids
Combining in-situ mixing with geogrid reinforcement for very soft subgrades (CBR < 2%). We excavate 300–400 mm, mix with granular borrow and a biaxial geogrid, then compact in layers. Effective for access roads and temporary haul routes in the Shepparton floodplain.
Typical parameters
Top questions
How much does soil stabilisation for roads cost in Shepparton?
The typical cost ranges between AU$1,420 and AU$5,030 per lane-km depending on the stabilisation depth, additive type, and site access. A full design-and-verify package including laboratory testing and a trial strip is usually AU$2,800–$4,200. Final pricing depends on the soil volume and the required strength target.
What tests are needed before designing a stabilisation mix?
We always run Atterberg limits, linear shrinkage, particle size distribution, and a modified Proctor compaction test (AS 1289.5.2.1). For Shepparton clays we also do the Eades & Grim pH test to determine the initial lime consumption. A soaked CBR at 98% MDD gives the baseline strength. These tests take about 10 working days.
Can soil stabilisation be done in wet conditions?
Lime stabilisation can proceed when the soil moisture content is within 2% of OMC. If the site is saturated after rain, we may need to pre-dry by disc harrowing or delay until the water table drops. Cement stabilisation is more sensitive to moisture; we avoid it when the surface is visibly wet or when groundwater is within 0.5 m of the treatment depth.
How deep should stabilisation be for a local road in Shepparton?
For residential streets with light traffic, 200 mm of stabilised subgrade is usually enough. For collector roads and heavy haul routes, we recommend 300–400 mm. The depth is confirmed by DCP testing after stabilisation to ensure the treated layer extends through the full active zone of the clay, typically 0.6–1.0 m below formation level.