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.

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

The CBR Test was formulated by the California State Highway Department, where the CBR Test is a penetration test replicating that of wheel loads, determining the mechanical strength of the subgrade and/or subbase.

CBR Test – Gravel Particles <20mm

A CBR Test is performed on the subgrade and/or sub-base of the road, where the maximum particle size does not exceed 20mm. Where particle sizes exceed 20mm, a Modulus of Subgrade Reaction Test is required (see below).

The CBR Test uses a fully loaded Sub Surface 4WD vehicle, jacked up to provide a stable deadweight. 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 is a type of CBR Test which are performed on the subgrade and/or sub-base of a pavement, where particle sizes are 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 and a hydraulic jack is used 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?

A CBR Test or a Modulus of Subgrade Reaction Test should be undertaken every 20 to 30 metres, to determine the CBR Value of the subgrade and/or sub-base as a percentage, where the value can be used to design the pavement in accordance to The Department for Transport’s Manual for Roads and Bridges, Volume 7, Section 2.

Subject to site conditions and test depths, we can undertake up to 10 CBR Tests and between 5 – 7 Modulus of Subgrade Reaction Tests per day and provide fast mobilisation and results with a professional, reliable and competitively priced service.

Whom to Contact

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

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