A plate bearing test can produce pages of load readings, settlement figures and graphs, but the most important question for a contractor is much simpler: what do the results actually mean for the construction work?
The test records how the ground, formation or prepared platform responds when a known load is applied through a rigid steel plate. The directly measured information is relatively simple: applied force and settlement. The engineering meaning comes from how those measurements change as the pressure increases.
That distinction matters. A plate bearing test does not produce a universal “pass” number, it does not automatically determine the ultimate bearing capacity of the ground, and it does not prove that an entire working platform is satisfactory because one location performed well.
The key message: a plate bearing test measures local load-settlement behaviour at a defined location, using a defined plate and loading arrangement. Whether the result is acceptable depends on the pressure actually achieved, the settlement recorded and the project-specific acceptance criteria set by the responsible engineer or designer.
Jump to: What the test measures | BS 1377-9:2025 | Load vs pressure | Reading the report | Settlement | Plate size | Working platforms | Bearing capacity | CBR, LWD and DCP | Common mistakes | Checklist | FAQ
What Does a Plate Bearing Test Actually Measure?
A plate bearing test, also commonly called a plate load test, applies vertical force through a circular steel plate placed onto the material being assessed. Settlement of the plate is measured as the applied load increases. The resulting data allows a load-settlement relationship to be produced. This is the core output of the test.
| Parameter | What It Means | Measured or Derived? |
|---|---|---|
| Applied force | The vertical force applied through the hydraulic loading system. | Measured, normally expressed in kN. |
| Settlement | Downward movement of the plate as load is applied. | Measured in mm. |
| Bearing pressure | Applied force divided by the contact area of the plate. | Calculated, normally expressed in kPa or kN/m². |
| Load-settlement curve | Shows how ground deformation develops as pressure increases. | Derived from the recorded test data. |
| Residual settlement | Permanent settlement remaining after unloading where an unloading cycle is undertaken. | Derived from displacement readings. |
Values such as allowable bearing pressure, modulus of subgrade reaction or equivalent CBR are different. These are engineering interpretations or derived parameters and should not be confused with the raw measurements made during the test.
BS 1377-9:2025: The Current UK Standard
The current British Standard is BS 1377-9:2025 — Methods of test for soils for civil engineering purposes. In-situ tests. The 2025 edition replaced BS 1377-9:1990, which is now withdrawn. For new work, project teams should therefore check that specifications, testing instructions and reports refer to the current standard where applicable.
That does not mean historic test results produced legitimately to the earlier standard suddenly become meaningless. Older reports remain records of the testing undertaken at the time, but their method and relevance should be understood when those results are used on a current project. STRUCTinspect has covered the wider implications of the standard update separately. The important point for result interpretation is that the standard defines the testing method; it does not provide one universal settlement limit that automatically makes every formation or working platform pass or fail.
Load in kN vs Bearing Pressure in kPa
One of the most common mistakes in plate bearing reports is confusing force with pressure. Load is the total force applied by the hydraulic system and is normally expressed in kilonewtons (kN). Bearing pressure is that force distributed over the area of the test plate. It is expressed in kilopascals (kPa) or kilonewtons per square metre (kN/m²). Numerically, 1 kPa equals 1 kN/m².
Pressure = Applied Force ÷ Plate Area
This is why the plate diameter must always be stated when interpreting a load in kN.
This is why the plate diameter must always be stated when interpreting a load in kN.
For example, applying the same 100 kN force through different plate diameters produces very different pressures:
| Illustrative Plate Diameter | Approximate Plate Area | Pressure at 100 kN |
|---|---|---|
| 300 mm | 0.0707 m² | Approximately 1,414 kPa |
| 450 mm | 0.1590 m² | Approximately 629 kPa |
| 600 mm | 0.2827 m² | Approximately 354 kPa |
The same 100 kN force therefore does not represent the same test when the plate diameter changes.
How to Read a Plate Bearing Test Report
A useful plate bearing report should allow the project team to reconstruct what was actually tested and compare the measured response with the design requirement.
| Report Item | What to Check | Why It Matters |
|---|---|---|
| Test location | Drawing reference, coordinates, grid or clearly marked position. | The result represents that location, not automatically the entire site. |
| Test level | Formation, capping layer, platform surface or other specified level. | Testing the wrong level can make the data irrelevant to the design question. |
| Plate diameter | Actual diameter used during the test. | Controls contact area and affects the volume of ground influencing the result. |
| Maximum force | Peak load achieved in kN. | Needed to calculate the actual maximum test pressure. |
| Maximum pressure | Pressure actually achieved in kPa. | Must be sufficient to answer the project's design question. |
| Settlement readings | Settlement at each load stage. | Shows how deformation develops as loading increases. |
| Reaction arrangement | Excavator, kentledge, vehicle or other reaction arrangement. | An inadequate reaction can prevent the required test pressure being reached. |
| Acceptance criteria | Required pressure and allowable settlement supplied for the project. | Without an acceptance basis, the report provides measurements rather than a meaningful project pass/fail decision. |
What Does Settlement Mean?
Settlement is the downward movement of the plate under load. The number becomes meaningful only when it is considered alongside the pressure at which it occurred. For example, a report showing only 1 mm of settlement may initially look excellent. But if the test only reached 150 kPa while the project needed evidence at a significantly higher pressure, the low settlement does not demonstrate performance at the required load. The entire load-settlement curve therefore matters.
Near-Linear Behaviour
A relatively consistent relationship between increasing pressure and settlement can indicate predictable ground response within the test range. It should not automatically be described as proof that the ground has unlimited additional capacity.
Increasingly Non-Linear Behaviour
If settlement begins increasing disproportionately as pressure rises, the ground may be moving away from relatively stiff behaviour towards yielding or greater permanent deformation. The significance depends on the material, loading history and project acceptance criteria.
Sudden Settlement
A sudden increase in settlement with little additional load can indicate local failure or punching behaviour and requires engineering review. Testing should not simply continue because a nominal target pressure has not yet been reached.
Residual Settlement
Where unloading is part of the test procedure, some of the movement may recover as the load is removed. Settlement remaining after unloading is residual or permanent deformation. The ratio between recoverable and permanent movement can provide useful information about the behaviour of the tested material, but there is no universal residual-settlement percentage that independently defines a pass for every construction application.
There is no universal “25 mm means pass” rule for plate bearing testing. Acceptance should be defined for the actual structure, working platform, plant loading and design requirement.
Why Plate Diameter Matters
Plate diameter affects more than the simple pressure calculation. It also affects the zone of ground contributing to the measured response. A relatively small plate primarily influences material close to the surface. A larger loaded footprint affects a greater volume of ground. This creates an important limitation where a strong granular layer sits over a weaker subgrade.
A small plate may record very little settlement because it is predominantly assessing the compacted platform material near the surface. A much larger piling rig track, crane pad or outrigger can influence the ground differently and may mobilise weaker material beneath the platform. For this reason, the test plate should not be selected simply because it is the easiest plate available in the testing vehicle. The testing arrangement should relate to the engineering question the project is trying to answer.
A high result from a small plate is not automatically evidence that a much larger plant footprint will behave in the same way. Plate size, platform thickness, underlying layers and actual plant loading all need to be considered by the designer.
Plate Bearing Tests on Working Platforms
Plate bearing tests are frequently requested on piling mats and working platforms supporting tracked plant, cranes and other heavy equipment. The test can provide valuable local evidence about settlement response at the tested point. What it cannot do is replace the working platform design.
Working platform performance also depends on factors including:
- platform thickness and material;
- strength and condition of the underlying subgrade;
- drainage and water conditions;
- plant track or outrigger geometry;
- platform deterioration and trafficking;
- local trenches, excavations and services;
- geogrid or reinforcement where incorporated;
- construction quality and maintenance.
The BRE BR470 Working platforms for tracked plant: Good practice guide and the Federation of Piling Specialists working platform framework provide wider context for platform design and control. For more on this subject, see Plate Load Test for Working Platforms: What Site Teams Need to Know. The important distinction is that a plate bearing test is evidence for the working platform assessment. It should not be presented as a universal certificate approving the entire platform.
Does the Test Measure Bearing Capacity?
Not necessarily. On many construction sites, the loading system reaches the specified maximum test pressure before the ground reaches an identifiable ultimate failure condition. If the ground sustains 400 kPa and the test stops because that was the specified target pressure, the correct statement is that the tested location was loaded to 400 kPa and exhibited the recorded settlement response.
It is not automatically correct to state that the ultimate bearing capacity is 400 kPa. Likewise, if the reaction vehicle begins to lift before the intended test pressure is reached, the maximum figure recorded may simply represent the capacity of the reaction arrangement, not the capacity of the ground.
| Report Statement | What It Actually Means |
|---|---|
| Maximum test pressure: 300 kPa | The ground was subjected to a maximum pressure of 300 kPa during that test. |
| Settlement at 300 kPa: 3.2 mm | The plate moved approximately 3.2 mm at that pressure under the stated test conditions. |
| Ultimate bearing capacity: 300 kPa | This statement requires an engineering basis. It should not be inferred merely because 300 kPa was the highest pressure applied. |
Plate Bearing Test vs CBR, LWD and DCP
Plate bearing, CBR, Light Weight Deflectometer and Dynamic Cone Penetrometer tests are sometimes discussed as though they provide interchangeable numbers. They do not.
| Test | Main Measurement | Typical Use |
|---|---|---|
| Plate bearing test | Static load-settlement response. | Formation, working platform and ground response under sustained loading. |
| CBR | Penetration resistance expressed as California Bearing Ratio. | Pavement and subgrade assessment. |
| LWD | Dynamic surface deflection and stiffness-related response. | Rapid compaction and uniformity assessment. |
| DCP | Penetration resistance with depth. | Identifying variability and weaker layers beneath the surface. |
An empirical relationship may sometimes be used to derive an equivalent CBR from other measured parameters. That is not the same as directly carrying out a CBR test. Particular care is required on layered working platforms. A mathematical conversion developed for a relatively uniform subgrade should not automatically be applied to a composite system containing aggregate, geogrid and a weaker underlying formation. See also Light Weight Deflectometer Test: What It Measures on Construction Sites and CBR Test in Construction: What the Result Means for Subgrade Design.
What About Ev1 and Ev2?
Another common source of confusion is the use of Ev1, Ev2 and the Ev2/Ev1 ratio. These deformation modulus concepts are associated with plate loading procedures such as DIN 18134. They should not automatically be presented as though they are standard BS 1377-9:2025 outputs. If Ev1 or Ev2 values are required by a project, the specification should identify the applicable method and acceptance criteria. A test performed to a DIN procedure should be reported as such rather than simply being labelled as a BS 1377 plate bearing test.
Stiffness is not the same as bearing capacity. A deformation modulus describes load-deformation behaviour under the relevant test method. It does not independently prove ultimate shear resistance or overall platform stability.
Common Plate Bearing Test Mistakes
| Mistake | Why It Matters | Better Approach |
|---|---|---|
| “The ground passed at 250 kN.” | kN is force, not bearing pressure. | State plate diameter, applied force and calculated pressure. |
| Treating maximum test pressure as ultimate capacity. | The test may simply have stopped at the specified load or reaction limit. | Report the maximum test pressure and measured response accurately. |
| Using a generic settlement limit. | Different structures and plant have different tolerance requirements. | Obtain project-specific acceptance criteria from the designer. |
| One test used to approve an entire platform. | Ground conditions can vary substantially across a site. | Use a test plan based on platform area, variability and project risk. |
| Directly converting every plate result to CBR. | Empirical correlations may not apply to layered or reinforced platforms. | Use the test method and parameter actually required by the specification. |
| Ignoring the reaction arrangement. | Insufficient kentledge can stop the test before the target pressure is achieved. | Plan the required reaction load before mobilisation. |
Checklist Before Booking a Plate Bearing Test
- Purpose: state exactly what engineering question the test needs to answer.
- Standard: confirm the required test method and current standard reference.
- Location: provide drawings, grid references or marked test positions.
- Test level: confirm formation, sub-base, working platform surface or other level.
- Plate diameter: confirm the plate required by the design or test brief.
- Target pressure: obtain the required pressure from the engineer or designer.
- Settlement criterion: define the allowable movement at the required pressure.
- Loading sequence: identify any project-specific requirements.
- Reaction load: provide suitable plant or kentledge capable of supporting the intended test load.
- Ground description: confirm what layer or material is being assessed.
- Reporting: confirm required plots, photographs, equipment details and interpretation.
- Acceptance responsibility: identify who will review the measured data against the design criteria.
Need Plate Bearing Testing?
For an accurate quotation, provide the test locations, test level, required plate diameter, target bearing pressure, settlement criteria and proposed reaction arrangement. Where these parameters have not yet been defined, they should be confirmed by the geotechnical engineer, temporary works designer or other competent designer responsible for the intended loading case.
Who Decides Whether the Result Passes?
The testing company measures and reports what happened during the test. It should record the actual applied force, calculated pressure, settlement, location, plate size, equipment and other relevant observations. Where written acceptance criteria have been provided before testing, the measured results can be compared directly with those requirements.
What the testing provider should not do is invent a generic design criterion after the test. A statement such as “passed at 300 kPa” has little engineering value unless the project had already established that 300 kPa and the associated settlement limit were the required acceptance criteria. For working platforms and temporary works, final acceptance remains part of the wider engineering and temporary works control process.
Evidence-Based Summary
A plate bearing test measures load-settlement behaviour at a specific location.
Applied force is measured in kN. Bearing pressure is calculated from that force and the area of the test plate and is expressed in kPa or kN/m².
A low settlement figure only has meaning if the required test pressure was actually achieved.
The maximum pressure applied during the test is not automatically the ultimate bearing capacity of the ground.
Plate diameter and ground layering affect what volume of material contributes to the measured response.
Equivalent CBR correlations should not be treated as direct CBR measurements, particularly on layered or reinforced working platforms.
A plate bearing test provides engineering evidence. It does not, by itself, certify an entire working platform or replace its design.
FAQ: Plate Bearing Test Results
What does a plate bearing test measure?
It measures the settlement response of the ground beneath a rigid plate as vertical load is applied. Applied force and settlement are recorded, with bearing pressure calculated from the plate area.
Is a plate bearing test the same as a plate load test?
The terms are commonly used interchangeably in UK construction. The important point is to define the actual test method, plate size, target pressure and reporting requirements.
What is a good plate bearing test result?
There is no universal result that is “good” for every project. The measured settlement must be assessed at the required pressure against the acceptance criteria defined for the particular loading case.
Does low settlement automatically mean the ground passes?
No. Low settlement under an inadequate test pressure does not demonstrate how the ground will behave at the required design pressure.
Is there a universal maximum settlement under BS 1377-9:2025?
The article research did not identify a universal project pass/fail settlement limit applicable to every plate bearing test. Acceptance should be defined for the actual design and intended use.
Does the maximum test pressure equal bearing capacity?
Not automatically. It may simply be the specified maximum load or the highest pressure the available reaction arrangement could achieve.
Can plate bearing results be converted directly to CBR?
A plate bearing test does not directly measure CBR. Empirical correlations may be used in appropriate circumstances, but they should not be treated as universally valid, particularly on layered or reinforced systems.
Can one plate test approve a complete working platform?
No. The result represents the tested location and loading arrangement. The wider working platform assessment must consider ground variability, platform design, drainage, construction quality, plant loading and the chosen testing regime.
Why does plate size matter?
Plate diameter affects both the pressure created by a given force and the volume of ground contributing to the measured response. A smaller plate should not automatically be assumed to represent the behaviour beneath a much larger plant footprint.
What happens if the reaction excavator starts lifting?
The required test load may not have been achieved. The highest pressure recorded before the reaction becomes unstable should not automatically be interpreted as the ground's ultimate capacity.
Are Ev1 and Ev2 BS 1377 results?
Ev1 and Ev2 are associated with deformation-modulus plate loading procedures such as DIN 18134. If those parameters are required, the project should specify the appropriate test method rather than assuming they are standard outputs from a BS 1377-9:2025 test.
Primary Technical References
The primary British Standard reference is BS 1377-9:2025 — Methods of test for soils for civil engineering purposes. In-situ tests.
For working platforms, project teams should also consider BRE BR470 — Working platforms for tracked plant: Good practice guide and the Federation of Piling Specialists Working Platform Certificate framework where applicable. Pavement and subgrade applications should be interpreted against the relevant project specification and current highways design requirements rather than relying on generic conversion formulae. The official standards and design guidance should be consulted for detailed test procedures, calculations and project-specific requirements. This article explains how common plate bearing test results should be understood but does not reproduce the full standard test method.
Source Context and Technical Note
This article is a STRUCTinspect technical explainer intended to help contractors, engineers, temporary works teams and project managers understand what plate bearing test results mean in practical construction terms. Plate bearing testing provides localised evidence about ground response under a defined loading arrangement. It does not replace geotechnical design, working platform design, inspection, drainage control, maintenance or engineering judgement.
This article does not provide geotechnical, structural, temporary works, legal or contractual advice. Test locations, plate size, loading sequence, target pressure, settlement acceptance criteria and interpretation should be confirmed by the competent engineer, designer or specification author responsible for the intended construction loading case.
