California Bearing Ratio Test Services from ACS
At ACS, we carry out in-situ California Bearing Ratio (CBR) testing and reporting to help you understand how your ground will perform under load. Our experienced team uses modern, calibrated equipment to deliver accurate, reliable results for a wide range of construction and infrastructure projects across the UK.
What Is California Bearing Ratio Testing?
The CBR test was originally developed by the California Division of Highways in the 1930s and is now a recognised standard method under BS 1377-9. It remains one of the most widely used ways to assess subgrade strength for highways, pavements, and earthworks.
In simple terms, CBR testing measures how resistant a soil is to penetration. This resistance is expressed as a percentage value (the CBR value), which indicates how well the ground can support loads and resist deformation.
Engineers use this data to design pavements and foundations, assess whether existing ground is suitable for construction, and identify where ground improvement may be required. Understanding ground conditions early is key to reducing risk, avoiding delays, and making informed design decisions.
Our In-Situ CBR Testing Methods
We offer a range of in-situ California Bearing Ratio (CBR) testing methods to suit different ground conditions, materials, and site constraints. ACS clients can have peace of mind that all testing is carried out in accordance with relevant British and European standards and tailored to meet your specific project requirements.
Calculation of Nominal CBR Value (Incremental Plate Load Test)
Where ground conditions or material size limit standard CBR testing, we can use plate bearing tests to determine an equivalent (nominal) CBR value.
How it works:
- A circular steel plate is placed on the ground surface
- Load is applied in controlled increments
- Settlement is measured at each stage
- Results are used to calculate soil stiffness and correlate to a CBR value
This approach is particularly useful for coarse materials and where larger particle sizes are present.
Calculation of Nominal CBR Value (Dynamic Cone Penetrometer)
The Dynamic Cone Penetrometer (DCP) test provides a rapid assessment of ground strength, especially where access is limited.
How it works:
- A metal cone is driven into the ground using a sliding hammer
- The depth of penetration per blow is recorded
- Results are used to estimate CBR values across different soil layers
This method is commonly used for preliminary investigations, remote or restricted-access locations, and profiling strength variation with depth. While less precise than direct CBR testing, it offers a practical and efficient alternative when conditions require it.
The Role of California Bearing Ratio Tests
CBR testing plays an essential role in early-stage planning and on-site verification. It provides the data needed to assess ground performance and support safe, efficient design.
You can use CBR testing to support:
- Subgrade evaluation – Understand the strength and consistency of underlying soils.
- Design optimisation – Inform pavement thickness and foundation design.
- Construction quality control – Verify that ground conditions meet specification.
- Material selection – Compare the suitability of different fill or sub-base materials.
- Comparative analysis – Assess variation across a site or between locations.
CBR test services are widely used for roads, car parks, industrial yards, and general civil engineering works. It’s also valuable for assessing existing ground conditions as part of site investigations.
Why Choose ACS for CBR Testing?
ACS provides California Bearing Ratio testing and consultancy services to clients across the construction and civil engineering sectors.
From our main laboratory in Poole, Dorset, we support projects with both on-site testing and expert guidance. Our Operations Manager and senior technicians are available to help you select the right testing approach and interpret your results.
- UKAS accredited since 1990
- Comprehensive CBR test services with UK-wide reach
- Testing carried out to British and European Standards
- Experienced, CSCS-qualified site technicians
- Clear, accurate, and timely reporting
At ACS, we’re dedicated to delivering reliable data and a straightforward service. You’ll know what’s being tested, why it matters, and how it applies to your project. If you’re planning a new development or need to assess existing ground conditions, our team is ready to help.
Contact us for California Bearing Ratio (CBR) Testing
Frequently Asked Questions
What is the California Bearing Ratio?
California Bearing Ratio is a measure of how strong a soil is compared to a standard crushed rock material. It’s expressed as a percentage, with higher values indicating stronger ground that can support heavier loads.
How do you calculate the California Bearing Ratio?
CBR is calculated by comparing the load required to penetrate the test soil with the load required to achieve the same penetration in a standard material.
Formula: CBR = (Test Load ÷ Standard Load) × 100
CBR testing in the UK is typically carried out at specific penetration depths, and results may be taken at multiple points to assess variation across a site.
How long does a CBR test take?
A standard in-situ CBR test typically takes around 30 minutes per location, depending on site conditions and accessibility.
What is the maximum particle size for CBR testing?
In-situ CBR testing is generally suitable for materials with particle sizes up to 20mm. For coarser materials, alternative methods such as plate bearing tests may be more appropriate.
Please see below for a list of the services provided by ACS:
Geo-Environmental Consultancy
The ACS Geo-Environmental Consultancy Department has been operating as part of ACS for over 10 years.
On-Site Testing Services
ACS offers a comprehensive range of professional on-site testing, all carried out by our fully trained site technicians.
Aggregates and Soils Testing
From our main laboratory in Poole, Dorset, ACS provide quality testing and material consultancy for the construction and civil engineering industry.
Bituminous Testing
ACS carries out testing on new bituminous binder material and testing on hardened material for physical and chemical properties. Circa pre 1980’s Tar (Carcinogenic effects) was also used as a binder, ACS staff can sample and test materials to assess if Tar was used.
Concrete Testing
Concrete was the first service to be offered by ACS back in 1987. Since then, we have increased our scope to cover a wide range of UKAS Accredited testing methods on fresh and hardened concrete.
Mortar and Screed Testing
ACS can sample and test new and hardened mortar. Hardened mortar for mix proportions and constituents, new mortar for compressive and flexural strength.
Natural Stone Testing
Our newly refurbished stone testing laboratory has given us the opportunity to expand our testing scope. In addition, we have increased production and improved on our turnaround of samples.
Site Laboratory Services
Over the last 35 years, ACS have supplied custom fitted site laboratories with technicians to many construction sites and projects worldwide.