In-Situ California Bearing Ratio (CBR)
Site Test
The in-situ California Bearing Ratio (CBR) test measures the strength of soil directly on site by assessing its resistance to penetration. The test determines how much pressure is required to push a standard plunger into the ground. The greater the resistance to penetration, the higher the CBR value, indicating stronger ground capable of supporting construction loads.

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The Process

The test is carried out using a CBR testing rig positioned over the test location. A cylindrical plunger of standard size is pushed into the soil at a controlled rate while the applied force is recorded. The resistance offered by the soil is compared with a standard reference material to calculate the CBR percentage.

The Reason

Subgrade strength is a key factor in pavement and foundation design. The in-situ CBR test provides a direct measurement of soil strength without the need to remove and transport samples to a laboratory. This allows engineers to quickly verify whether the ground conditions meet the required design specifications.

The Application

In-situ CBR testing is commonly used in road construction, car parks, and other paved areas to assess subgrade strength. The results help engineers determine whether the existing ground is suitable for supporting pavement layers or if additional treatment, compaction, or replacement of materials is required.

Frequently Asked Questions

Why is in-situ CBR testing important for my project?

The test confirms whether the ground has sufficient bearing capacity to support pavement or construction loads. Amtest testing helps ensure the subgrade meets the project specification before construction continues.

When should an in-situ CBR test be carried out?

The test is typically performed during ground investigations or after subgrade preparation but before pavement layers are installed. Amtest can carry out testing at the stage most relevant to your project.

Will Amtest provide documentation of the results?

Yes. Amtest provides clear test reports detailing the measured CBR values, helping contractors and engineers demonstrate compliance with design and specification requirements.

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In-Situ California Bearing Ratio (CBR)

The California Bearing Ratio (CBR) test is a simple and effective method to assess the strength of soil and sub-grade materials on construction sites. This test evaluates the material's resistance to penetration, providing essential data for pavement and foundation design.

The Process

  1. Testing Procedure
    • A plunger is pressed into the soil at a controlled rate over a standard area.
    • The pressure required to penetrate the soil is measured and recorded.
  2. Comparison with Standard Material
    • The measured pressure is compared to the pressure needed to penetrate a standard crushed rock material under identical conditions.
  3. CBR Value Calculation
    • The result is expressed as a percentage, where higher CBR values indicate stronger and more stable surfaces.

Why Is This Test Important?

  • Design Validation: Ensures the subgrade or base layers meet the load-bearing requirements for roads and pavements.
  • Material Suitability: Determines whether the existing soil is suitable for construction or requires improvement.
  • Project Planning: Helps engineers design layers and thicknesses to optimise pavement performance and longevity.

The CBR test is crucial for assessing ground conditions, ensuring safe and reliable construction practices. Contact us to arrange on-site CBR testing and get precise results for your project.