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In a past Explainer, we talked about the preparations that take place underground as a prerequisite to new highrise construction. For existing buildings that need additional support, the process of underpinning is performed. Today's Explainer describes what this delicate practice is, and the different types of underpinning that may be employed.
The foundations of a building may need added support depending on the circumstances. Earthquakes and floods may cause the foundations to move due to weakened soil conditions. Building expansions and the addition of more floors will likely also necessitate increased foundation strength. This is done through the excavation of soil underneath the existing foundation, which is then usually replaced by concrete, a technique known as mass concrete underpinning.
There are several other different types of underpinning:
- Beam and base: A reinforced concrete beam is installed above the building footings or in replacement thereof, which transfers building loads to mass concrete bases.
- Mini-piled: Cylindrical supports — or piles — are driven into the ground at deep depths to transfer foundation loads to more stable soils.
- Expanding resin injection: A relatively new approach to underpinning, this procedure involves the injection of a structural resin and hardener mix underground, which then creates a chemical reaction that expands and compacts weaker soil, raising the structure above and healing cracks in the building.
As the world grows denser and land becomes scarcer, building new structures adjacent to and above existing ones will likely remain a common practice. Underpinning provides the stability demanded by these activities in a safe and thorough manner.
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