Underpinning facts for kids

Underpinning is a cool process in construction where engineers make the foundation of an old building or other structure stronger and more stable. Think of it like giving a building new, super-strong shoes!

Why would a building need new "shoes"? Here are some reasons:

• The original foundation might not be strong enough anymore.
• The way the building is used might have changed. Maybe it was a small house and now it's a busy office!
• The soil under the foundation might have changed. Sometimes the ground can sink a bit (this is called subsidence), or maybe the builders didn't know exactly what kind of soil was there when they first built it.
• New buildings being built nearby can sometimes dig up the soil that supports older foundations.
• Sometimes, it's cheaper to fix the old foundation than to tear down the whole building and start fresh.

What is Underpinning?

Underpinning is like a special repair job for a building's base. Imagine a building's foundation as its feet. If these feet start to get weak or sink, the whole building can be in trouble. Underpinning adds extra support to these "feet" to make sure the building stays safe and steady.

Why Do Buildings Need Stronger Foundations?

Buildings need strong foundations to stand tall and safe. Over time, many things can affect a foundation. For example, if a building was built a long time ago, its foundation might not be as strong as modern ones. Or, if heavy machinery is used nearby, or if there's a lot of rain that washes away soil, the foundation can become weak. Underpinning helps fix these problems.

How is Underpinning Done?

There are different ways to underpin a building, but they all involve adding new support under the existing foundation.

• Adding new concrete: Sometimes, workers dig small sections under the foundation and pour new concrete to make it thicker and stronger.
• Using steel pins or piles: Long, strong steel rods or concrete columns, called piles, can be pushed deep into the ground. These piles go past the weak soil until they reach very strong ground, giving the building a solid new base.
• Jet Grouting: This is a high-tech method where a special liquid is injected into the soil at high pressure. This liquid mixes with the soil and then hardens, creating strong columns of soil-cement that support the foundation.

Each method is chosen based on the type of building, the soil, and how much support is needed. It's a job for expert engineers and construction teams!

Images for kids

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  Sketch of a cast in situ RC cantilever needle beam on micro piers or piles. Access to inside not needed.

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  ketch of a standard needle beam on micro piers or piles. Inside access needed.

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  Sketch of concrete pier underpinning with the possibility of raising foundations.

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  ketch showing the traditional method of needling a wall to reduce the weight on the foundations during underpinning work.

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  Underpinning the foundations of a railway bridge using a timber box crib to support the bridge. A completed concrete pad underpinning can be seen at the bottom right.

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  Drilling machines using jet grouting

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  Close to the drilling head