Underpinning is a construction technique that involves strengthening and stabilizing the foundation of a building or structure. It is a crucial process, especially in areas like Sydney, where soil stability issues and foundation failures can lead to substantial damages and safety hazards.
This thorough guide, brought to you by A1 Underpinning, Sydney’s leading underpinning experts, will provide an in-depth understanding of different underpinning, its importance, applications, and how they can benefit home and building owners in Sydney.
Foundation Failures and Soil Stability Issues
Foundation failures occur when the soil beneath a structure is unable to bear its load or has become unstable due to geological factors, poor drainage, nearby construction activities, or natural causes such as extreme weather events.
Soil stability issues can manifest as settlement, cracks in walls, and even partial or complete building collapse. In Sydney, certain soil types and local environmental conditions can exacerbate these problems.
Having your building underpinned can address these issues by providing additional support to the foundation, transferring load to more stable soil, and preventing further damage to the structure. As various factors can affect a foundation and soil stability, several underpinning techniques and materials have been developed to cater to diverse needs within the construction industry.
Types of Underpinning Systems and Their Applications
1. Mass Concrete Underpinning
Application: Traditionally used method suitable for shallow foundations, typically residential and low-rise commercial spaces.
Pros: Cost-effective, and a proven method that has been used for decades.
Cons: Not suitable for deep foundations or areas with limited access.
This technique involves excavating a series of pits beneath the existing foundation and filling them with concrete. The concrete is then cured, forming “underpinning blocks” that act as a new, more stable base for the structure.
Mass concrete is ideal when foundation issues arise from shallow soil settlement or when the existing foundation load needs to be redistributed.
2. Beam & Base Underpinning
Application: Suitable for structures experiencing settlement, such as terraced houses, commercial and residential spaces.
Pros: More effective than mass concrete underpinning for buildings with differential settlement, easily adaptable to various soil conditions.
Cons: May require more extensive groundwork and cause disruptions to the surrounding area.
This method comprises a reinforced concrete beam that transfers the load from the existing foundation to newly constructed concrete bases or piles. The beam is designed to distribute the load evenly across the new bases, effectively counteracting any differential settlement issues. Beam & base underpinning is often used when a building’s foundation is affected by soil properties, such as clay shrinkage, which causes uneven settlement.
3. Mini-Piled Underpinning
Application: Ideal for deep foundations, limited access or environmentally-sensitive areas, such as industrial complexes or heritage buildings.
Pros: Can reach greater depths compared to other methods and is minimally invasive, allowing for limited environmental impact.
Cons: Requires specialized equipment and can be more expensive than other techniques.
Mini-piled uses small diameter steel or concrete piles, driven or bored into the ground at specified intervals. These piles extend deep into the stable soil or rock strata, transferring the structure’s load and ensuring stability. Mini-piles are appropriate for addressing a wide range of foundation issues, including deep excavation-triggered settlement, ground subsidence or landslides.
Now that you understand the types of underpinning their pros, cons and applications, it will be easier for you to make a decision on which type to use for your structure.
If you need help, feel free to contact Mark at A1 Underpinning. Mark and his team can handle all facets of underpinning and structural restoration in Sydney and surrounding areas.