Optimum Compliance Benchmark

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Benchmark your project

Because you and others in the supply-chain rely upon testing companies, like Simtec, to pass-off your work, we created the Optimum Compliance BenchmarkTM (OCB).

We have documented the practices and procedures that produce the conditions for an optimum compliance outcome, going far beyond minimum compliance requirements (see the sample below).

Using Simtec historical data, we found that approximately 95% of the compliance levels not being met were due to low-quality or incorrect materials being used. The remaining 5% was simply a result of not adhering to best practices. The Simtec OCB datasheets help mitigate those risks.

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Simtec Materials Testing Ltd will in no event be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising out of, or in connection with, the use of this website or our OCB (optimum Compliance Benchmark) guides. Any reliance you place on such information tips, help and advice is therefore strictly at your own risk.

Example OCB Datasheet

Unbound Layer Testing

CBR (Determination of the equivalent California Bearing Ratio using the plate bearing test)

Validation of results

By using a UKAS accredited testing organisation results will be accepted by all UK Government agencies, including Highways England and local authorities.

Referencing standard(s)

BS1377: Part 9: 1990 Clause 4.1 Design Manual for Pavement Foundations CD 225 IAN73/06 Rev 1:2009 (Withdrawn)

Establishing testing layers

In most cases (depending on the layer thickness) formation and capping requires a 450mm diameter plate and a Sub-base requires a 300mm diameter plate.

Adhere to specified min CBR % for the relevant Local Highways Authority or Highways England.

Preparation & compaction

Formation & Sub-Formation: Proof roll the Subgrade before test. Capping Layer materials require compaction to the requirements of Table 6/1 – Series 600 of the SHW.

Type 1 Sub-Base: Ensure appropriate thickness and adequate compaction. Avoid segregation of stone materials and ensure smooth level test surface.


Kentledge provision should be in excess of 6 tonnes and have an accessible flat area to seat the jack. A Back Hoe digger or a 360 excavator is ideal.

Length of time

Kentledge is required for the duration of the test. Testing at each location typically lasts 30 mins. Individual test duration will vary according to the ground conditions.

Weather conditions

Weather does not adversely affect the testing regime. However, rain over a prolonged period will distort the CBR value of both the formation and sub-base layers. Avoid testing when the surface is frozen or affected by frost and snow or is saturated.