What Is A Plate Load Test And How Is It Done?

Ever wondered how engineers figure out whether the soil at a site can actually support a building, machine, crane, road, or even a heavy container?

Well we often test the soil right there in the field.

And among all tests, one of the most reliable tests for shallow foundations is the plate load test, something me and my team do a lot on construction sites.

You can think of it as a strength test for the ground. Here, we place a heavy steel plate on the soil, push down on it using a hydraulic jack, and observe how much the soil compresses under different loads. 

From that simple insight, we get valuable numbers like: 

• Bearing capacity (how much pressure the soil can safely handle),
• Settlement behavior (how much the soil will compress under load), and
• Overall suitability for shallow foundations, roads, working platforms, and crane pads.

In this blog, I will walk you through all things plate load testing. You’ll know: 

• What this test is all about 
• How it works
• Why is it so important 
• What equipment we used
• How we interpret results

So, let’s get started. 

Key takeaways

• A plate load test measures how soil reacts to pressure.
  
• It helps determine if the soil can support a building or structure.
  
• Engineers apply gradual loads to see how much the soil settles.
  
• Results show safe bearing capacity, settlement behavior, and soil suitability.
  
• Plate load tests are key for shallow foundations, crane pads, and roads.
  
• It’s a real-world test, not just based on soil reports or lab results.
  
• The test can take 3-6 hours, depending on the soil type.
  
• Larger plates give more accurate results for bigger foundations.
  
• The test helps confirm if the ground is ready to bear heavy loads.

What is a plate load test? 

In simplest words, a plate load test is among those construction material testing where you load a steel plate placed on the ground and measure how much the soil settles.

That’s it.

You’ll gradually increase load using a hydraulic jack and record settlement after each increment. 

And you can use these measurements to understand how strong the soil is and how it behaves under real loads.

This is one of the most direct and reliable tests for shallow foundation design. That’s because you’re loading the soil exactly the way a footing, column base, slab, or crane platform would load it.

Don’t Let Site Conditions Delay Your Project

From geotechnical reports to environmental assessments, and more, our ACI-certified experts deliver the data and insights you need to stay on schedule.

Contact Us

Why is a plate load test done?

You might be curious why engineers like us go through all the trouble of hauling a steel plate, jacks, gauges, and a reaction frame to a construction site. 

It is simple.

A plate load testing gives you the most realistic information about how the soil will behave under actual loads. 

There is no guessing or lab assumptions, just the ground responding to pressure right where you plan to build.

All in all, here’s why engineers do this test at your construction site: 

1. To determine safe bearing capacity

One of the biggest questions in foundation design is: How much pressure can this soil safely handle?

Now, plate load testing answers that by applying load step by step and watching how the soil reacts. 

From this, you can calculate the safe bearing capacity of soil or the maximum pressure the soil can take without risk of excessive settlement or failure. This is the number engineers use to size footings and slabs confidently.

2. To predict settlement

Even if the soil is strong enough, it will still compress a bit when you put load during construction.

Now, the question really is how much will it compress?

For instance: 

• A small amount of compression is normal.
• A large amount of compression can cause problems.
• And uneven settlement is the worst as it can tilt foundations, crack walls, and damage machinery.

A load test gives a clear load-settlement curve that shows exactly how the soil will behave as loads increase. This is critical for structures that are sensitive to movement.

3. To verify geotechnical investigation results

Soil reports from geotechnical site investigations are based on boreholes, standard or cone penetration tests, and lab tests. And they give you a good picture of the soil profile. 

But they are still indirect measurements.

A plate load test, on the other hand, tells you how the soil performs in the field, under a real load, at the exact spot where you’re planning to build.

This helps confirm, and sometimes correct, the assumptions made during soil investigation, especially in sites where the soil varies a lot over short distances.

4. To check suitability for certain structures

Plate load testing is very useful when you want to confirm that the ground can support certain types of foundations or working areas. 

In fact, it is usually done before building or installing:

• Shallow foundations and footings
• Machine foundations that need stable support
• Wind turbine foundations
• Temporary works platforms
• Heavy crane pads
• Embankments
• Road base and subgrade layers
• Container yards
• Piling and rig platforms

In all these cases, the loads can be high and safety is critical, so real settlement data becomes essential.

5. For quality control during construction

Sometimes the soil is fine during design, but conditions change during construction. 

Maybe it rains, the soil gets disturbed, or fill is placed. 

Now, a quick load test helps confirm that the ground is still capable of supporting the planned load.

Contractors and owners love this test for that reason, as it gives immediate on-site assurance that everything is safe before moving ahead.

TL;DR, here’s why plate load tests are important:

Reason	Description
Determine Safe Bearing Capacity	Helps calculate how much pressure soil can safely handle.
Predict Settlement	Measures how much the soil will compress under load, helping avoid problems.
Verify Geotechnical Results	Confirms soil profile and behavior based on real-life testing.
Check Suitability for Structures	Ensures soil is suitable for foundations, crane pads, roads, and other structures.
Quality Control During Construction	Verifies soil’s capability as construction proceeds.

Where is plate load testing most useful?

Plate load testing becomes critical when: 

• The structure is shallow
• The loads are moderate to heavy
• You need real settlement data
• Soil layers are soft to medium stiff
• The soil is heterogeneous (meaning it varies a lot)
• You’re building something temporary but safety-critical (like a crane pad)

Note: It is less useful for deep foundations or when soil variability becomes significant below the test depth.

How is a plate load test done? 

A plate load test might look complicated when you see all the equipment on site. But the actual process is very systematic. 

Think of it like checking how strong and steady the ground is by pressing on it gradually and watching how it responds. 

Here’s how the whole thing happens in the field.

STEP 1: Excavation of the test pit

The first step is preparing the spot where the test will be done. Here, a small pit is excavated down to the exact depth where the foundation is planned. 

This is important because you don’t want to test the surface soil if your actual footing will sit deeper.

The pit is usually made big enough (about five times the width of the plate) so there’s plenty of space to work. Also, there are no side walls to interfere with the load distribution. 

Now, once the pit is ready, the bottom surface is cleaned, levelled, and made firm. And any loose soil, stones, or debris are removed because even small irregularities can affect the settlement readings.

STEP 2: Placing and leveling the plate

Next up, the steel plate is placed right at the center of the pit. 

Here, the soil surface isn’t perfectly smooth, a thin layer of sand is spread to help the plate make full contact. 

Engineers then check and adjust the plate until it is perfectly level.

This may sound like a small detail, but it’s actually one of the most important steps. That’s because if the plate is even slightly tilted, the load won’t be applied uniformly, and the settlement readings will be inaccurate.

STEP 3: Setting up the hydraulics and reaction frame

Once the plate is in place, the hydraulic jack is positioned directly on top of it. 

Above the jack, a reaction system is set up. This could be a heavy steel frame, a weighted truck, or concrete blocks. 

This reaction system acts as the anchor against which the jack pushes down.

Also, dial gauges or digital settlement sensors are mounted on a separate reference beam to measure settlement. The beam stands independently and it doesn’t touch the jack, the plate, or the reaction frame. 

This way, the gauges only measure the soil’s movement, and not any vibration or shifting of the equipment.

STEP 4: Applying the seating load

Before the real loading starts, a light seating load is applied. Think of this as gently pressing the plate down just enough to close any tiny gaps and make sure everything is properly in contact.

And after holding it for a short while, the load is released.

This step helps the system settle in, removes slack, and ensures the test starts from a stable and accurate baseline.

STEP 5: Applying incremental loads

Now the actual testing begins. 

Here, the load is applied in small amounts and increased gradually. For instance, 5 kN, 10 kN, 20 kN, 30 kN, and so on. 

The exact values depend on the type of soil and the purpose of the test.

Now, each time a new load is applied, it’s held until the settlement slows down or stabilizes. This waiting period can be just a few minutes for sandy soils or slightly longer for clayey soils. 

During every increment or load increase, engineers carefully record:

• The load applied
• The settlement readings from dial gauges
• The time
• Any visible changes such as cracks, tilting, or sudden drops

Some engineering teams also note the temperature, especially in sensitive projects, because it can affect the instrumentation.

This step-by-step loading helps build a clear load-settlement curve showing how the soil behaves under increasing pressure.

STEP 6: Reaching maximum load

In this step of plate load testing the loading continues until one of three things happens:

• The soil shows signs of failure (sudden or rapid settlement)
• The test reaches the planned maximum load, often 1.5 to 2 times the design load
• The settlement goes beyond a set limit, such as 25 mm

This helps identify the soil’s ultimate load capacity and how close it is to a failure condition.

STEP 7: Unloading and observation

After reaching maximum load, the jack pressure is gradually released in stages. 

Just like loading, unloading is also controlled and measured. Here, the rebound, or how much the soil springs back, gives valuable information about how much of the settlement was elastic (recoverable) and how much was plastic (permanent).

This final step helps engineers understand the soil’s stiffness and long-term behavior under footing loads.

TL;DR, here’s how plate load testing is done:

Step	Action
Step 1: Excavation	Dig a pit at the foundation depth to prepare the testing area.
Step 2: Plate Placement	Place the steel plate and ensure it’s level for accurate readings.
Step 3: Setup Hydraulics	Position hydraulic jack and reaction frame for load application.
Step 4: Seating Load	Apply a light load to settle everything before the actual test.
Step 5: Apply Incremental Loads	Gradually apply and record increasing loads on the plate.
Step 6: Maximum Load	Continue loading until the soil reaches its maximum capacity or fails.
Step 7: Unloading	Gradually unload and measure the soil’s rebound (elastic vs. permanent settlement).

Bonus: Which equipment is used for plate load testing?

A typical plate load testing setup includes the following equipment:

1. Steel loading plate

• Circular or square
• Usually 300 mm to 750 mm diameter
• At least 25-30 mm thick
• One plate or multiple stackable plates

2. Hydraulic jack

Used to apply load onto the plate.

3. Reaction system

The jack used this to push the following:

• Heavy reaction frame
• Loaded truck
• Concrete blocks
• Steel beams

Note: The reaction system must be heavier than the expected load.

4. Settlement measuring system

Dial gauges or displacement transducers fixed to a rigid reference beam.

5. Load measurement

Load cell or proving ring to measure actual load applied.

6. Test pit

You excavate to the actual foundation level to place the plate on the real soil surface.

TL;DR, here are the equipment you need for plate load testing:

Equipment	Description
Steel Loading Plate	Typically 300-750 mm in diameter, used to apply the load to the soil.
Hydraulic Jack	Used to apply pressure onto the steel plate.
Reaction System	Includes heavy steel frames, concrete blocks, or trucks used to anchor the load.
Settlement Measuring System	Includes dial gauges or digital sensors to measure settlement.
Load Measurement	Load cells or proving rings to measure the applied load.
Test Pit	Excavated to foundation depth to place the steel plate.

What are the advantages and disadvantages of plate load testing?

As you can see, plate load testing is a useful method for understanding how soil reacts to loads. It provides real on-site data, is quick to perform, and gives clear results. 

However, it has some limitations too. 

Here’s a quick look at the advantages and disadvantages of load testing: 

Advantages:

• Directly measures soil behavior under load.
• Provides quick, reliable results (same day).
• Easy-to-understand load-settlement curve.
• Great for shallow foundations and machine foundations.
• Useful for crane pads, piling platforms, and working surfaces.
• Helps validate your geotechnical report and ensures quality control during construction.

Disadvantages:

• Doesn’t simulate large-scale foundations.
• Only tests near-surface soil.
• Requires heavy reaction loads, which can be tricky.
• Needs space and time for setup.
• Won’t capture deep or variable soil layers.

When to use plate load testing and when not to? 

Use plate load test when:

• You need shallow foundation data
• You want real, physical settlement measurements
• You’re designing machine foundations
• You’re building a crane pad, platform, or road layer
• You want quick field verification

Don’t use plate load test when: 

• The structure is deep
• Soil layers vary significantly at deeper levels
• You need shear strength at multiple depths
• You need detailed soil classification

Don’t Let Site Conditions Delay Your Project

From geotechnical reports to environmental assessments, and more, our ACI-certified experts deliver the data and insights you need to stay on schedule.

Contact Us

Conclusion 

By now, you know what a plate load test really is and how it works on construction sites. 

This is a simple test that uses a steel plate, a hydraulic jack, and a reaction frame. But it provides some of the most valuable soil behavior data you can get on a construction site.

It’s fast, practical, and useful for shallow foundation design, working platforms, roads, and machinery bases.

Got more questions or want a plate load tester for your construction site?

We’ve got you covered!

At NewTech Engineering, we are the most seasoned field and lab testing experts in the Carolinas with decades of hands-on experience. And we’ve got all your field testing needs covered on a budget. 

You might also want to read: How To Test Concrete PSI? 

FAQs about plate load testing 

What is a plate load test in simple words?

A plate load test is basically a strength test for the ground. You place a steel plate on the soil, push down on it using a hydraulic jack, and measure how much the ground settles. 

From this, we understand how strong the soil is and whether it can safely support a building, crane, machine, road, or any other structure.

How long does a plate load test take?

Most tests take about 3 to 6 hours from start to finish. The exact time depends on the type of soil and how many load increments are needed. 

Sandy soils settle quickly, so the test is faster. Clayey soils take longer because settlement happens more slowly.

What is the typical plate size used?

A static plate load testing uses plates of standard diameters like 300 mm, 450 mm, 600 mm, and 750 mm. 

The size is chosen based on the expected load and the type of foundation being considered.

Larger plates give more realistic results, especially for big footings or machine bases.

How much settlement is acceptable?

Generally, engineers expect the plate to settle somewhere around 15-25 mm during the test. 

But the exact allowable settlement depends on the type of structure and the design codes being followed. 

For instance, machine foundations often need stricter limits because too much movement can cause vibration issues.

Is plate load testing better than standard or cone penetration tests?

Not really better, just different. Here’s how: 

• Plate load testing tells you how the soil behaves under a real load. It gives actual settlement data.
  
• Standard and cone penetration tests tell you about soil strength at various depths and help identify soil layers.

Both types of tests complement each other, and engineers often use them together for a complete picture.

Where is plate load testing most useful?

Plate load tests are especially handy when you’re working on shallow or surface-level structures. They’re commonly used for:

• Shallow foundations
• Footings and rafts
• Machine foundations
• Crane pads
• Road base and subgrade layers
• Temporary working platforms
• Container yards and laydown areas

Basically, if you need to know how the ground behaves right near the surface, PLT is a great choice.

Does plate size affect results?

Yes, very much. 

Larger plates tend to give results that match real foundations more closely because they cover more soil area. 

Smaller plates sometimes show higher bearing capacities than what you would actually get for a building footing. 

That’s why choosing the right plate size is important.

Can plate load testing be done on rocky ground?

Yes, it can. 

On rocky or very stiff ground, you’ll see extremely small settlements even at high loads. This usually indicates very strong support conditions. 

However, special care is needed because the equipment must be able to handle those higher loads safely.

How deep should the pit be?

The test pit is excavated to the actual foundation level, which is usually 1 to 2.5 metres deep depending on the project. 

Testing at foundation depth ensures the readings reflect the soil that will actually support the structure.

What happens after the test?

Once the test is complete, engineers analyze the load and settlement data and convert it into a load–settlement curve. 

From this curve, they calculate the ultimate bearing capacity, safe bearing capacity, and expected settlement.

The results are then compiled into a report and used to make foundation recommendations for your project.