CBR Testing: Prove Subgrade Strength for Roads, Pavements & Airfields
California Bearing Ratio (CBR) testing is a penetration test used in civil and geotechnical engineering to assess the strength of subgrade soils and granular base materials—a key input for road and pavement design. First developed in the 1930s, the method compares a material’s resistance to penetration against a reference crushed stone (assigned 100% CBR), giving engineers a practical strength index.
What CBR helps you determine
CBR results are commonly used to inform:
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required pavement thickness
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subgrade suitability and construction risk
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whether stabilisation (lime/cement) is needed
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likely load-bearing performance for roads and airfields
How laboratory CBR testing works
In the lab, material is recompacted into a mould at either its natural moisture content or optimum moisture content. Testing can also be carried out in a soaked condition to simulate saturated ground. It’s common to test stabilised materials (e.g., lime or cement treated) to confirm strength improvement where soft soils would otherwise underperform.
In the UK, CBR testing is typically undertaken to BS 1377:1990 and BS EN 13286-47 (unbound and hydraulically bound mixtures).
Why choose The Testing Lab PLC?
At The Testing Lab PLC, we deliver CBR testing with consistent preparation, reliable results, and clear reporting—so you can make confident decisions on design, earthworks suitability, and stabilisation performance.
Need CBR testing? Contact The Testing Lab PLC to discuss samples, soaked/non-soaked requirements, and turnaround.
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