If you want your build to have the most stable foundations, it’s essential to be aware of the load-bearing capacity of piling. Piles are long columns usually made from concrete or steel, which are then driven deep into the ground to form the foundation of a building.
Have you ever wondered how end-bearing piles are strong enough to hold the weight of high-rise, residential, and infrastructure buildings? It’s because of their load-bearing capacity and ability to transfer a building’s weight to a more stable underground layer.
Read on to learn more about the load-bearing capacity of piling foundations.
What is load-bearing capacity?
In simple terms, load-bearing capacity is the maximum weight a foundation can hold before failure, usually indicated by a bend, crack, or collapse. The load-bearing capacity of a pile can differ depending on the pile material, soil type, moisture content, and structural weight.
Why is load-bearing capacity an essential consideration for piling foundations?
Safety is the most important consideration in any structural build. By determining load-bearing capacity and adhering to it, you can confirm that the pile system can safely support your structure over its lifespan without risk of failure.
It’s also essential to calculate the load-bearing capacity of piling for:
- Cost-savings and efficiency: If your project fails to adhere to the correct load-bearing calculations, you risk over- and under-designing. For example, you could waste money and labour on installing and purchasing longer or wider piles, or require a complete demolition and rebuild if you’ve installed undersized piles.
- Compliance with design codes: In the UK, it’s a legal requirement to adhere to design and engineering codes, as it confirms that the piles can support ultimate loads (worst-case scenario weight limits). The correct calculations will also help your build maintain serviceability, reducing the risk of significant settlement.
- Serviceability: Serviceability refers to a building’s structural ability to resist loads throughout its lifespan, enhancing its usability and user comfort. Following load-bearing calculations will reduce the settlement risk of wall and floor cracks, misalignments, and drainage issues.
- Adapting to available soil conditions: By calculating the load-bearing capacity of your piles, you can ensure that they are long enough to reach a secure and suitable load-bearing layer and that the pile shaft and surrounding soil interact as expected. If not, your pile could be pushed down to a weaker layer, also known as a punching failure, which can be catastrophic.
Types of piles and their load-bearing capacity
As we’ve already mentioned, the load-bearing capacity of your piles can vary depending on:
- Soil type
- Pile material
- Pile diameter and length
- Pile installation method
- Groundwater conditions
- Pile spacing
While this information should never replace your site-specific calculations, here are the typical load-bearing capacity ranges for different types of piles:
Driven displacement piles
- Light loads: 50 – 200 kN
- Medium loads: 200 – 1,000 kN
- Heavy loads: 1,000 – 5,000+ kN
Bored piles
- Small diameter: 150 – 500 kN
- Large diameter: Up to 5,000+ kN
Screw piles
- Light residential and commercial applications: 50 – 500 kN
- Heavy-duty industrial applications: Up to 1,000+ kN
Continuous Flight Auger (CFA) piles
- 300 – 2,500 kN
Mini piles
- 100 – 1,000 kN
How to calculate the load-bearing capacity of a pile
The load-bearing capacity of your piling foundations depends on two aspects:
- The end-bearing capacity (pile tip resistance)
- The skin friction capacity (pile shaft resistance)
These two calculations make up the ultimate load-bearing capacity of a single pile.
Total pile capacity = end bearing + skin friction
Let’s take a round concrete pile with a 0.4m diameter as an example, and say it is being pushed 10m deep into firm clay.
How to calculate the end-bearing capacity of a pile
To calculate the end-bearing capacity of a pile, use this formula:
Area = π × (diameter / 2)²
Using the example measurements, this would translate into:
Area = 3.14 × ( 0.4 / 2)² 2 = 3.14 × 0.2² = 3.14 × 0.04 = 0.1256m²
Once a specialist team has determined soil strength, you will know how much load the soil can support — this is measured in kN per square metre.
Let’s say, for this example, that the soil can take 500 kN per square metre.
You can then calculate the end-bearing capacity:
End bearing = 0.1256 × 500 = 62.8kN
How to calculate the skin friction capacity of a pile
Next, calculate the side area of the pile to find out how much load is supported via friction along the sides of the pile:
Side area = Perimeter × Depth
Perimeter = π × diameter = 3.14 × 0.4 = 1.256m
Side area = 1.256 × 10 = 12.56m²
If the soil provides 40kN per m² along the sides:
Skin friction = 12.56 × 40 = 502.4kN
Determining total load-bearing capacity of Piling
Add the end-bearing and skin friction figures together:
Total capacity = 62.8 + 502.4 = 565.2kN
Adding a safety factor
A safety factor must be applied to your calculation to ensure the pile can safely withstand unexpected loads. This accounts for real-world uncertainties and misjudgements in material quality and calculations.
A safety factor of 1.0 would mean that you’re using the pile’s full capacity with no wiggle room, which is very dangerous. So, for this example, we’ll say that the safety factor is 2.5:
Safe load of the pile = 565.2 / 2.5 = 226.1 kN
Trust in WL Piling for reliable, legally-compliant piling services
With over 50 years of experience, our team can deliver a variety of professional piling services across the North West to meet your project’s needs.
From foundation and grundomat piling to driven and mini piling, we have the expertise and equipment to get your build off the ground.
Get a free quote today by getting in touch with our team. Call 07525 497 677, email chris@wlpiling.co.uk, or fill in our simple online contact form.
