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15.11.2021, 14:28
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What are pile caps and how to locate them?
Although pile caps are hidden away underground, they still play an important role in any major construction project. They help to create a stable foundation for large buildings and structures and without them, structures could sink into the ground.
In this article, we look at what a pile cap is and how you can easily locate them with the help of a GPR survey.
What are pile caps?
Pile caps are concrete structures that play a key part of large-scale building projects involving things like high-rise buildings and bridges. They serve as the foundation for columns and piers, transferring the load from the columns to a group of piles or a single pile beneath the ground.
They need to be rigid and capable of transferring the load from the column to the pile or group of piles. Because of this, they are typically made out of reinforced concrete or precast concrete. Depending on design requirements and the arrangements of piles in the soil, the shape and size of the pile cap can vary.
The construction of a pile cap involves several steps. First, the pile is driven into the soil to the desired depth. The top of the pile is then trimmed to the required height and levelled. Reinforcing bars are then placed around the pile in a cage-like structure, and concrete is poured to create the pile cap.
Once the concrete has cured (given adequate moisture, temperature and enough time to achieve the desired properties to be fit for purpose), the pile cap will be ready to support the load from the column or pier. Pile caps need to withstand the weight of the structure, as well as any lateral forces that could impact it like wind or seismic activity.
Pile caps are usually used when the soil conditions at a
building site are not able to adequately support the load of a building's
foundation on its own. To prevent the building from sinking into the soil,
piles are driven deep into the ground to create a solid foundation. Pile caps
are then used to distribute the load of the building's foundation onto the
piles.
If the soil is soft and prone to movement, the building or structure will remain solidly in place because of the piles it is built on.
How to locate pile caps?
When starting a construction project on an existing building
or structure, it is essential to locate the pile caps accurately to ensure any
work does not damage the foundations.
GPR (Ground Penetrating Radar) can be used to locate pile caps. An underground detection survey is an unobtrusive way to locate a pile cap as it uses radar to scan the sub-terrain area without the need to dig into the ground.
Due to their small size and their location makes them challenging to locate, even by experienced GPR surveyor.
Once you have the results of your GPR survey and you know where the piles are located, mark their centrelines on the ground using spray paint or another type of marker.
The marks need to be visible and accurate as they will be
used as reference points when locating the pile caps.
A GPR survey will also help you measure the distance between the centreline of each pile. It is very important to work out the distance between each pile as this will determine the size and shape of the pile cap. The gap between the piles is usually kept at 2.5 times the diameter of each pile. This makes sure they do not interfere with one another which could potentially weaken the stability of the structure’s foundation.
info
If you need a survey to locate pile caps or have any other questions email us on info@kbsurveys.co.uk or give us a call on 020 3931 5759.
We would be more than happy to discuss your project.
How thick should a pile cap be?
Pile caps should be at least 500mm in thickness. Any free
edges only need to be at least 300mm thick. A pile cap should have a clear
overhang of 150 mm, although it is acceptable if they are at least over 100mm.
What are pile caps made of?
A pile cap is usually made of thick concrete. They need to be solid to hold the weight of any structures placed on them.
Our GPR services
At KB Surveys, we consistently deliver quality service from
our dedicated team of highly skilled engineers, supported by our
customer-focused management team. Our range of GPR services can help you with
your subsurface investigation and we offer a responsive, independent and
innovative approach to meet your needs at the right price.
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04.11.2022
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