Shepparton's growth as a regional hub has driven demand for reliable road infrastructure across the Goulburn Valley. The city's expansion into former floodplains and irrigated farmland means subgrade conditions vary significantly within short distances. Our team has worked on subgrade investigations for arterial roads, industrial access routes, and residential subdivisions throughout the Greater Shepparton area. We combine local knowledge of the Shepparton Formation soils with laboratory testing to deliver pavement designs that handle both seasonal moisture changes and heavy agricultural traffic. Before specifying pavement thickness, we always run granulometría and Atterberg limits to classify the foundation layer.
A 10% increase in subgrade CBR can reduce required pavement thickness by 15-20 mm, saving significant material costs over a 2 km haul road.
Method and coverage
- Dynamic cone penetrometer (DCP) surveys for rapid in-situ CBR profiling along proposed alignments
- Modified Proctor compaction (AS 1289.5.2.1) to establish optimum moisture content for each soil layer
- Soaked CBR testing at field density to simulate worst-case moisture conditions during spring
Regional considerations
Shepparton sits on the Shepparton Formation, a sequence of Quaternary alluvial clays, silts, and sands with variable clay content. Shallow groundwater tables between 1.5 and 4 m depth are common near the Goulburn River, creating risk of capillary rise into the subgrade. Without proper drainage design, these conditions lead to loss of bearing capacity and differential heave. We recommend installing piezometers and monitoring moisture migration when designing subgrade for low-lying sections. The instrumentación geotécnica we deploy tracks real-time changes during construction.
Standards that apply
AS 1289.6.1.1 (CBR test), AS 1289.5.2.1 (Modified Proctor), Austroads Guide to Pavement Technology Part 2: Pavement Structural Design (2017)
Complementary services
Subgrade Investigation & Soil Classification
We drill test pits and boreholes to log soil profiles, collect undisturbed samples, and run classification tests including particle size distribution and Atterberg limits. Results feed directly into pavement design parameters.
CBR & Compaction Control for Subgrade
In-situ CBR testing with DCP and field density tests using nuclear gauge or sand replacement. We verify that compacted subgrade meets specified density and moisture requirements before base placement.
Subgrade Improvement Design
For weak or expansive soils, we specify lime or cement stabilisation depths, geotextile separation layers, or replacement with select fill. Designs follow Austroads guidelines and include construction specifications.
Typical parameters
Top questions
What CBR value is typical for Shepparton subgrade soils?
Most natural subgrade in Shepparton ranges between CBR 2 and 8 when tested soaked at 98% modified maximum dry density. Heavier clay zones can drop below CBR 2. We recommend soaked CBR testing because the seasonal water table rise saturates the subgrade during winter and spring.
How much does a road subgrade design investigation cost in Shepparton?
A standard investigation for a local road covering test pits, classification tests, and CBR testing typically ranges between AU$1,670 and AU$4,680 depending on site access, number of test locations, and the complexity of soil conditions. We provide a fixed-price quote after reviewing the project scope.
Do I need lime stabilisation for my Shepparton road project?
Lime treatment is often justified when the subgrade CBR sits below 3 or when linear shrinkage exceeds 12%. For Shepparton's grey cracking clays, adding 3-5% hydrated lime reduces plasticity index by 10-15 points and improves workability. We run a lime-modification test (AS 1289.5.5.1) to determine the optimum dosage before specifying treatment.