CBR (California Bearing Ratio) testing is a method used to determine the load bearing capacity of road materials and subgrade soils. It is used to determine the ability of the material to resist penetration under load and is vital in pavement and road designs.

Our CBR Testing Services

Our experienced geotechnical team at Atlas Engineering offers a range of CBR testing services tailored to your project needs, all conducted in accordance with relevant Australian Standards, including AS 1289.6.1.1.

• Laboratory CBR Testing: Conducted on samples remoulded in the laboratory to specific moisture content and density conditions. This includes:
  • Soaked CBR tests (typically 4-day soak) to simulate worst-case saturation conditions.
  • Unsoaked CBR tests for conditions where saturation is not anticipated.
• Field (In-situ) CBR Testing: While less common for design due to variability, we can advise on appropriate field methods if required.
• Material Evaluation: Testing quarried materials, recycled materials, and stabilised soils for suitability in pavement construction.
• Compliance Testing: Verifying that compacted materials on site meet the specified CBR design values.

We provide detailed NATA-endorsed reports that clearly present the test results, methodologies, and relevant site information.

The CBR Testing Process

Our standard laboratory CBR testing process generally involves the following steps:

1. Sample Collection & Preparation: Representative samples are obtained from your site or quarry. The material is prepared and compacted in the laboratory into standard CBR moulds at a specified moisture content and compactive effort (e.g., standard or modified compaction).
2. Soaking (if required): For soaked CBR tests, the compacted specimen, with a surcharge weight, is submerged in water for a specified period (typically 96 hours / 4 days) to measure swelling and simulate long-term moisture conditions.
3. Penetration Test: A standard plunger is forced into the soil specimen at a constant penetration rate (1.0 mm/min or 1.27 mm/min, depending on the standard variation). The loads required to achieve specific penetrations (typically 2.5 mm and 5.0 mm) are recorded.
4. Calculation & Reporting: The recorded loads are compared to standard loads for high-quality crushed stone. The CBR value is expressed as a percentage of the standard load. The higher values at 2.5 mm or 5.0 mm penetration (after correction if necessary) are usually reported as the CBR.