A plate bearing test measures how the ground behaves under load. A rigid steel plate is bedded onto the test surface and loaded in stages against a reaction, while the settlement is recorded. From that data an engineer can assess bearing capacity, settlement behaviour and the modulus of subgrade reaction, taken directly from the ground as built rather than from assumption. In the UK the test is carried out to BS 1377 Part 9, the standard for in-situ tests on soils for civil engineering purposes.
It is one of the most direct ways to confirm that a formation, a piling platform or a granular sub-base will carry the loads placed on it. This guide explains how the test is run, what it tells you, how it relates to working platform sign-off under BR 470, and how it differs from a CBR test.
How a plate bearing test works
The principle is simple. A steel plate is placed on a prepared, level test surface, and a hydraulic jack applies load to the plate against a reaction. The load is applied in increments; each stage is held, and the settlement of the plate is measured. Plotting load against settlement shows how stiff the ground is and how much it deforms under a known pressure.
The reaction that the jack pushes against has to come from somewhere. It is provided either by kentledge, meaning a stacked dead weight such as a loaded lorry, an excavator or concrete blocks, or by a machine positioned to act as the reaction. The choice depends on the load to be reached and the access on site, and it is agreed before the test so the correct reaction is available on the day.
What the test tells you
A plate bearing test is used to assess:
- Bearing capacity of a formation or foundation subgrade
- Settlement and deformation under a known applied load
- Modulus of subgrade reaction for slab and pavement design
- The performance of granular working platforms and piling mats
- Compacted fill, sub-bases and capping layers
- The suitability of a formation before foundations, slabs or hardstanding are built
The results let a designer check measured ground behaviour against the values the design assumed. Where the ground underperforms, that is far better discovered under a test plate than under a loaded structure or a tracking rig.
Working platforms and BR 470
One of the most common reasons for a plate bearing test is signing off a working platform. Before a piling rig or a crane tracks onto a granular platform, someone has to be confident the platform will carry it. BR 470, the BRE good practice guide to the design, installation, maintenance and repair of ground-supported working platforms for tracked plant, is the reference for that work.
A plate bearing test provides on-site verification that the completed platform performs in line with its design. The measured load and settlement data is presented so it can be checked against the platform design and BR 470, giving the temporary works coordinator or checking engineer the evidence to accept the platform, or to query it, before plant is allowed on. This is a safety-critical decision, and measured data is what supports it.
When you need one
Plate bearing tests are commonly required to sign off a working platform or piling mat before a rig or crane tracks onto it, at foundation formation level to confirm the ground meets the assumed design bearing value, before casting a ground-bearing slab or laying external hardstanding, to verify compacted fill or a granular sub-base after earthworks, and for temporary works checks where plant loads bear on made-up ground. In short, wherever a design needs validating against real ground conditions rather than published figures.
Common questions
What is a plate bearing test?
A plate bearing test, or plate load test, is an in-situ field test in which a steel plate is loaded against a reaction and the settlement is measured. It is used to assess the bearing capacity, settlement behaviour and modulus of subgrade reaction of the ground, giving a direct measurement of how a formation, sub-base or working platform performs under load. It is carried out to BS 1377 Part 9.
What standard is a plate bearing test carried out to?
In the UK, plate bearing testing on soils is carried out to BS 1377 Part 9, the code covering in-situ tests within the methods of test for soils for civil engineering purposes. Where the test is used to verify a working platform for tracked plant, the results are assessed against the design guidance in BR 470.
What is BR 470 and how does it relate to plate testing?
BR 470 is the BRE good practice guide to the design, installation, maintenance and repair of ground-supported working platforms for tracked plant. Plate bearing testing is one way to verify on site that a completed working platform performs in line with its design before piling rigs or cranes are allowed to track onto it.
Is a plate bearing test the same as a CBR test?
No. A plate bearing test measures the ground’s response to a loaded plate to assess bearing capacity and settlement. A CBR, or California Bearing Ratio, test measures the strength of a subgrade or sub-base and is more often used in pavement and road design. The two give related but different information, and the right test depends on what your design needs to confirm.
If you need a formation, sub-base or working platform verified against measured ground conditions, our plate bearing testing service brings the plate, jack, reaction arrangement and instrumentation to site and reports the data for sign-off against your design and BR 470. If your project also involves proving fixings once installed, our guide on anchor pull tests covers on-site load testing to BS 8539.