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Plate Bearing Ratio Test vs California Bearing Ratio Testing

The viewpoint of foundation designs has to start from the surface bearing strengths. Before construction of tall buildings and roads, soil load bearing tests have to be done. The test on the site ground is aimed at getting the soil properties. Plate bearing test, as well as California bearing test, are the main tests used today. The tests are conducted in the laboratory or on the site ground.

What Are the Distinguishing Factors?

1) The Main Purpose

Plate bearing Ratio is an investigation that aims to determine the actual strength as well as bearing capacity of ground awaiting a certain mass of construction, whereas CBR testing is penetration method that evaluates the ground ability as well as the powers of its subgrades and the base layers to hold a new carriage construction on it.

2) The Condition of Use

PBR is used where the testing involves large particle sizes or soils that have a harder texture. That is enabling the fact that the plates on the testing machine have a large surface area. On the other hand, CBR is suitable for areas where the particle sizes are small, such that they are not more than 20mm.
The limit to the small particle is due to be used in CBR devices, which typically have a small cylindrical surface that penetrates into the ground. The pressure obtained are rated against the set standard pressure required for uniform penetration. Those that correspond to 100 percent rate are the best ones.
Normally, PBR tests are used for designing of temporary structures such as crane outriggers pads. Then the results can be used as a base for groundwork as well as construction. The CBR test is used when measuring the pressure on the ground soil where the new road, pavement or any carriageway is going to undergo development.

3) The Aims of the Test

PBR is done to test maximum weights that a surface can hold firmly. That means that the results limit the construction weights, in some cases, the results may lead to abortion of plans to construct a building in certain places. Otherwise, the construction massiveness may be reduced if plans have to continue.
In some parts, the plate bearing test results may determine the depths of the groundwork that is going to be required. Contrary, CBR method aims at testing the thickness factor that is going to be needed for all materials to be used for construction. The test is done to make sure the construction will have the strengths of bearing possible pressures. Therefore, the CBR results influence the materials to be used in a building, which includes their natural properties such as size as well as density.

4) How It Is Performed

PBR is performed at the foundation level, but at times, it can be done on the surface that is slightly below the ground. The method involves the application of pressure on the surface that is under testing.
When it comes to CBR, penetration is the primary action required whereby, the machines cylindrical plunger is driven into the ground at a constant rate. Usually, a four-wheel drive vehicle is used to provide reaction weight for the purposes of force production. That because the test has to be done with real weighs that are available.
PBR requires a total of six tests mostly to be able to come up with a conclusion on a ground that would influence plans. However, the CBR requires at least eight tests for analysis as well as determination to be derived. The differences in testing are due to surface areas. It is easier to ascertain results for plate bearing than in the case of CBR that tests smaller areas regarding surface penetrated. For PBR, a large surface area is involved.
When it comes to PBR, tests can be done on the ground or testing of a sample in a lab setup. Both can be effective and reliable. For CBR, both site ground, and sample tests can also be done. It is more recommendable for CBR conduction on the site ground where you can test with real carriage vehicles to come up with results that are more reliable.

5) The Testing Process

The plate bearing test takes a straightforward process whereby, the plates undergo subjection to various pressure amounts, and the record making happens. The pressure exerted is added at a consistent rate. The records taken are then plotted on a graph to determine the bearing capacity value of the ground tested. On the other hand, the California bearing test is performed by measuring pressure amounts required in penetration by the plunger used on different surfaces of the site ground.

6) Other Strengths

When it comes to the possibility of defects, CBR offers more efficiency compared to PBR tests on the identification of defections that may occur during the tests as well as analysis.


- Both tests are done with aims to support and development of stable construction output. Both are investigative practices.
- The two tests apply to temporal foundations during building work on a site ground.
- Conduction of both tests comes before any construction work starts. In fact, they are the first things that must be done before continuing with the plans of construction. The test results can have significant impacts on the schedules, budget, materials to be used and many other influences.
If you require any site testing services contact us today to see how we can help you. We offer site testing right across the UK.

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