Sub Surface provide CBR (California Bearing Ratio) values for the design of pavements (roads) via a CBR Test. As described in BS1377: Part 9: 1990: Soils for Civil Engineering Purposes.

The CBR Test is a penetration test replicating wheel loads to determine the mechanical strength of a subgrade or subbase. The California State Highway Department created the CBR test in 1929.

If you require testing for working platforms, such as crane outrigger pads, piling mats, etc. please follow the link to Plate Bearing Test.

CBR Test – Gravel Particles <20mm

A CBR Test is performed on the subgrade of a road when the maximum particle size does not exceed 20mm. A Modulus of Subgrade Reaction Test is performed when particle sizes exceed 20mm (see below).

A fully loaded Sub Surface 4WD vehicle, jacked up to provide a stable deadweight, is used to perform the test. The test records the pressure required for a cylindrical plunger to penetrate the ground a minimum of 5mm, at a rate of 1.0 mm/min. The pressure recorded to penetrate the ground 2.5mm and 5.00mm is used to determine the CBR Value.

Modulus of Subgrade Reaction Test (CBR Value) – Gravel Particles >20mm

Modulus of Subgrade Reaction Tests are used to determine the CBR value when the maximum particle size is greater than 20mm. The test uses the same apparatus as a Plate Bearing Test, generally using a 600mm diameter plate. A tracked excavator (13tonne minimum) is required to provide a deadweight. This enables a hydraulic jack to apply pressure to the plate. The CBR Value is determined by the pressure required to penetrate the ground 1.25mm.

How Many CBR Tests Do I Need?

CBR Tests or Modulus of Subgrade Reaction Tests should be undertaken every 20 to 30 metres. A CBR Value of the subgrade and/or sub-base is calculated as a percentage. The results can then be used to design roads in accordance with HE-DMRB-P CD 225 Revision 1 Design for New Pavement Foundations.

Sub Surface can undertake up to 10 CBR Tests and between 5 Modulus of Subgrade Reaction Tests per day, depending on the site conditions and test depths.

We provide fast mobilisation and results, with a professional, reliable and competitively priced service.

Whom to Contact

If you would like a quote for CBR Testing or Modulus of Subgrade Reaction testing, please do not hesitate to contact your Regional Sub Surface Office.

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