Plate Bearing Test
test A plate bearing test is an in-situ test used in civil engineering to determine the strength and bearing capacity, stiffness, and settlement characteristics of the ground under a known load. The test provides accurate and reliable data on how the ground behaves when a load is applied, making it essential for assessing working platforms, temporary structures, and areas supporting heavy construction equipment.
Unlike laboratory tests, a plate bearing test reflects real site conditions, ground particle sizes, and compaction levels at the test location, helping engineers make informed decisions that support the overall project’s success.
What a Plate Bearing Test Measures
A plate bearing test determines:
- Ground bearing capacity and overall load-bearing capacity
- Ultimate bearing capacity of the ground
- Safe bearing capacity under a factor of safety
- Settlement characteristics and likely settlement
- Subgrade reaction and ground stiffness
- Actual strength and capacity of the ground
Because the test is carried out directly on the ground surface or in a shallow pit, it provides realistic insight into how the ground will behave beneath the foundation of a structure or platform.
How the Plate Bearing Test Is Carried Out
The plate bearing test is carried out in accordance with BS 1377 Part 9: 1990.
A circular steel plate (the test plate) of known plate diameter is positioned on prepared ground. Common plate sizes typically range from 300mm to 750mm, depending on ground conditions and loading requirements.
The test involves:
- Positioning the steel plate on the ground or in a shallow pit
- Applying load using a hydraulic jack and a load cell
- Increasing the load in controlled load increments
- Recording settlement at each stage using dial gauges
- Continuing until shear failure occurs or the plate begins to settle quickly
The load is applied gradually until the plate begins to show rapid settlement, indicating that the ground is reaching its failure condition. This is simply how a plate bearing test works.
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Load Application, Reaction Load, and Equipment
To do the test safely and accurately, we need to apply a reaction load to the load cell. That’s usually done using a tracked excavator; we typically use one that’s at least 15 tonnes in weight.
The other bits of equipment that we use in a plate bearing test are
- A tracked excavator or piling rig as a reaction load
- A hydraulic jack and load cell to apply the load
- A circular steel plate
- Settlement gauges measure how much the ground settles
The test simulates real loading scenarios for all sorts of things like crane bases, crane outriggers, piling mats, and working platforms.
Ultimate Bearing Capacity and Safe Bearing Capacity
The ultimate bearing capacity is calculated by dividing the total load value applied to the plate by the area of the steel plate:
Ultimate bearing capacity = total load ÷ plate area
The safe bearing capacity is then determined by applying a factor of safety (typically 3) to reduce the risk of excessive settlement or ground failure.
This process ensures that the ground can safely support the load required by temporary or semi-permanent structures.
Settlement Behaviour and Interpretation
When we’re doing a plate bearing test, we’re also keeping an eye on how much the ground settles. That tells us whether we need to be concerned about the settlement levels and whether we need to do any ground improvement or redesign before we can build on the site.
Plate Bearing Test vs CBR Test
The California Bearing Ratio (CBR) test assesses penetration resistance over a much smaller area and is typically used for pavements, roads, and slab design involving fine-grained soils.
A plate-bearing test:
- Covers a larger surface area. While the results of both tests give the same equivalent value, the capabilities of the plate bearing test make it more suitable for testing a larger surface area compared to a CBR test.
- It is more suitable for granular soils and larger particle sizes
- Provides direct load–settlement data
Results from a plate bearing test can be used to calculate an equivalent CBR value, allowing comparison with traditional CBR test results while offering more realistic performance data for temporary works.
Typical Applications
Plate bearing tests play a crucial role in verifying stability and safety for:
- Working platforms for piling rigs
- Crane outrigger pads and crane bases
- Piling mats and access routes
- Temporary haul roads and construction compounds
- Areas supporting heavy construction equipment
The test is commonly used to determine whether ground conditions are suitable before installing heavy machinery or temporary structures.
Advantages of Plate Load Test Services
There are a few key advantages to a plate bearing test. Here are some of them:
- It gives us the accurate results that we need to know how the ground will behave
- It’s suitable for all sorts of different soil types
- It’s a more realistic test than a CBR test for coarse materials
- It minimises the risk of construction failure
- It helps us comply with design requirements and keeps us safe
- It helps prevent ground collapse or excessive settlement
We can typically get the results of a test in 24 hours, and we can do a load of 4 to 8 tests a day; that’s a pretty quick turnaround. For projects that need spot-checking of heavy machinery, temporary working platforms, or structures that’ll be used only for a while, plate bearing testing is probably about as good as it gets when it comes to assessing their stability & safety.