What is underpinning?
Underpinning is a versatile construction technique used to strengthen the foundation of an existing building or structure. It involves excavating the soil below the existing foundation and replacing it with stronger and more durable materials, such as concrete or steel.
Underpinning Contractors use these techniques when the existing foundation is inadequate or unstable due to various factors, such as soil subsidence, water damage, or changes in the surrounding environment.
The technique is also used when the load-bearing capacity of the foundation needs to be increased to support additional weight or a new structure.
What are the different types of underpinning techniques?
There are several types of underpinning techniques used in construction, including:
- Mass concrete underpinning: This is the most common form of underpinning and involves excavating the soil in stages beneath the existing foundation and pouring concrete to create a new, deeper foundation. This technique is typically used for small to medium-sized structures with shallow foundations.
- Beam and base underpinning: This technique involves the installation of reinforced concrete beams and bases under the existing foundation, which provide additional support and stability. The beams and bases are installed in sections, and the weight of the building is transferred onto them as the soil is excavated.
- Pile underpinning: This technique involves the installation of piles, which are long, narrow columns made of concrete, steel, or timber, under the existing foundation. The piles are driven deep into the ground until they reach a stable layer of soil or rock, and the weight of the building is transferred onto them.
- Mini-piled underpinning: This is a variation of the pile underpinning technique but uses smaller diameter piles that are drilled into the ground rather than driven in. This technique is often used for sites with limited access or where noise and vibration need to be kept to a minimum.
- Resin injection underpinning: This technique involves injecting a high-strength resin into the soil beneath the foundation to create a solid support structure. The resin is typically injected through small holes drilled into the ground and can be used for a variety of soil conditions.
What is the process of underpinning?
The process of underpinning can be summarized in the following steps:
- Site preparation: The first step is to prepare the site for the underpinning process. This may involve removing obstacles, debris, and vegetation and securing the area to ensure safety during excavation and construction.
- Excavation: The soil is excavated in sections to expose the existing foundation, which may involve digging down to several meters. The excavation is typically done in stages, with each section being excavated and underpinned before moving on to the next section.
- Shoring: Temporary supports, such as jacks, props, or brackets, are installed to stabilize the existing structure during the excavation process. This is essential to prevent any collapse or movement of the building.
- Construction: The new foundation is constructed in sections using a chosen underpinning technique, such as mass concrete, beam, base, or pile underpinning. The choice of technique will depend on the project’s specific requirements, such as the soil conditions, the size and weight of the building, and the extent of the foundation damage.
- Backfilling: Once the new foundation is in place, the excavation is backfilled with soil, and any necessary repairs or finishing work is completed.
What are the applications of underpinning?
From Underpinning to around the world, Underpinning is used in a variety of construction applications, including:
- Foundation repair: Underpinning can be used to repair and strengthen existing foundations that have become damaged or unstable due to soil subsidence, water damage, or other factors.
- Building extensions: Underpinning in Berkshire is often used to support the existing foundation when building extensions or adding additional floors to a building.
- Retaining walls: Underpinning can strengthen retaining walls, which are structures that hold back soil or other materials.
- Basement conversions: Underpinning is commonly used in basement conversions to support the existing foundation and increase the ceiling height.
- Sloping sites: Underpinning can level sloping sites and provide a stable foundation for buildings or structures.
- Heritage buildings: Underpinning can be used to restore and preserve heritage buildings, which may have outdated or inadequate foundations for everyday use.