In civil engineering terms, ground bearing capacity is key to safe and economical construction. One of the most direct field test methods to determine in situ strength and design parameters is the plate load test or plate bearing test.
But when do you use a plate load test? In this post we’ll talk about scenarios where a plate load test is more useful, how it compares to other tests (like the CBR test which measures the California Bearing Ratio) and the practical steps in conducting a plate bearing investigation.
Top 9 Testing Tools for Landing Pages That Boost Conversion Rates
1. What is a Plate Load Test?
A plate load test (or plate bearing test) measures how the ground (subgrade, fill or natural soil) responds to a given load applied through a circular steel plate of a specified plate diameter.
The test plate is placed on the surface or at the intended foundation level (often in a shallow pit) and a gradually increasing load is applied using a hydraulic jack. Engineers observe the settlement of the plate at each load increment. From these test results you can:
- Safe bearing capacity (or ultimate bearing capacity with additional calculations)
- Subgrade reaction (often noted as the sub grade reaction or grade reaction)
- Strain modulus of the subgrade
- Potential equivalent CBR value (comparing to cbr test data)
This in situ test helps to check if the actual strength of the ground meets the required values for working platforms, crane pads, piling pads, foundation footings and more.
2. When do you use a Plate Load Test?
- Design of Shallow Foundations
- Plate load tests are useful for checking the bearing capacity and subgrade reaction at foundation level, for shallow pit foundations, pad footings or strip footings.
- By observing how a circular steel plate settles under design load, engineers can determine the safe bearing capacity and decide on plate size or thickness of structural elements.
- Working Platforms & Crane Pads
- Construction equipment like piling rigs or cranes applies high bearing pressure on working platforms or piling pads.
- A plate bearing test gives reliable results to check if the granular material or compacted soil can safely distribute these load demands, especially for crane outriggers that applies significant, localized load.
- Quality Control for Fill and Subgrade
- If you have areas with engineered fill or granular material, the plate load method is a cost effective way to check compaction adequacy and actual strength.
- Together with a cbr test, a plate load test can help you get an equivalent CBR (or equivalent CBR value) to meet site investigation requirements or design parameters.
- Comparisons and Verification of CBR Values
- While the California Bearing Ratio (cbr test) is widely used, the plate bearing method can give deeper insight on subgrade reaction for large loads.
- The plate load test can support (or verify) cbr value results, especially when the maximum particle size or the ground conditions are not suitable for standard cbr test procedures.
- Large or Specialized Projects
- High load structures, unusual subgrade conditions or construction equipment with special load requirements may need a larger reaction load and varying plate diameter to simulate real world test load scenarios.
- Examples are heavy industrial floors, large storage tanks, piling rig support areas and crane pads.
Raise Your Own raised License Plate Frame For Personal Use
3. What to look for
- Test Plate (Circular Steel Plate)
- Designed to specific plate diameter required, ranging from 300 mm to 750 mm (or more).
- Plate size varies depending on the design load and the in situ tests.
- Loading System (Hydraulic Jack)
- A hydraulic jack applies the test load to the test plate, the reaction load.
- Reaction load can come from a piling rig, a vehicle with crane outriggers or a dedicated reaction frame.
- Load Increment and Settlement Measurements
- Load increments are applied rapidly or in controlled manner and dial gauges record settlement (how the plate sinks).
- Each increment is held until settlement rate stabilizes, to get a reliable measurement for that load level.
- Data Analysis
- Test results are plotted to get bearing capacity or safe bearing capacity and to estimate subgrade reaction (or sub grade reaction modulus).
- By dividing the plate settlement under given load, engineers can scale up to full scale foundations.
4. Plate Load vs CBR Test
- Purpose: A cbr test is used for road or pavement design to classify subgrades by their California Bearing Ratio. The plate load test (or plate bearing test) is more focused on bearing pressure and structural loads.
- Load Simulation: Plate load simulates structural load at foundation level, while cbr test simulates wheel load penetration for roads.
- Equivalent CBR Value: Some engineers use plate load data to get equivalent CBR for design. But note that the two tests are different in scope and approach.
5. Tips for Good Plate Load Testing
- Choose the Right Plate Diameter
- Make sure you have the right plate diameter for your design load. Using plate diameter too small or too large can misrepresent the site conditions.
- Provide Sufficient Reaction Load
- The reaction load system (e.g. piling rig, truck or hydraulic jack) must exceed the maximum load required. Insufficient reaction load can invalidate the test results.
- Define Clear Load Increments
- Apply the load in uniform increments and allow settlement reading at each increment. Jumping loads too fast can mask the soil strain modulus.
- Subgrade Variations
- Do multiple in situ tests if soil properties vary across your site. The value of a single plate load test is limited if conditions are very different.
- Monitor and Record
- Use precise dial gauges and ensure stable referencing during the test. Changes in ambient conditions or poor equipment setup can affect the results.
- Compare with Others
- Combine plate load test data with site investigation requirements, such as borehole logs or cbr test results, to get the full picture of the sub grade.
What Is The Use of Raised License Plate Frames
Summary
When to use plate load test? Anytime you need direct in situ information on how soil or granular material will behave under real loads—especially for shallow pit foundations, piling pads, crane outriggers and working platform designs.
By applying a circular steel plate to the ground and measuring its settlement under a test load, a plate bearing test gives you cost effective and reliable results for civil engineering.
Whether you’re validating equivalent CBR value for cbr test or confirming the ultimate bearing capacity of your foundation level, plate load (or plate bearing) test is one of the simplest way to know the actual strength of the ground.
Plan well—choose the right plate size, ensure sufficient reaction load and follow good practices for the test—to get the design parameters you need for quality control in your next project. Contact Site Testing Services LTD for expert advice.
