Underpinning is a method that strengthens and stabilises existing foundations to combat issues like ground movement or changing use of properties.
Traditional underpinning methods typically involve excavating and replacing soil with concrete in various ways depending on your situation. Here are the primary forms of underpinning:
Mass Concrete
Mass concrete Underpinning Melbourne is the oldest and most traditional form of foundation underpinning. This technique involves extending existing footings down to deeper levels where stable soil with sufficient bearing capacity is present, by excavating box-shaped voids through different stages or pins and filling them with concrete. Next, dry sand-cement packing mortar is then used between new and old foundations to safely transfer load between them.
Underpinning is both time- and labor-consuming, yet often provides the best results in cases of foundation settlement. Homeowners prefer underpinning over mudjacking or polyurethane materials which do not offer permanent solutions to foundation settlement. As an added advantage, anti-heave precautions such as polythene sheeting or low density polystyrene sheets may also be installed to help protect underpinning from shrinkage or movement, especially important when constructed using shrinkable clay soil.
Mini-Piles
Micropiles can be an ideal way to underpinning foundations if conventional piles cannot be installed due to limited headroom or ground conditions. Their unique design enables loads to be transferred directly onto the soil with steel reinforcement starter bars and has compressive capacities of up to 500 tonnes.
Mini piles are an economical and reliable underpinning solution that are often employed for projects with restricted headroom or low headroom, or excavation support needs. Made from high strength small diameter steel casings with threaded bars allowing easy transportation in tight spaces for installation or transportation needs.
Mini piles can be utilized through different systems, including pile and beam, cantilever pile-cap and piled raft systems. When employing pile and beam systems, pairs of piles are constructed along either side of a wall with caps on top. These caps are then linked by a reinforced concrete beam that spans the length of the building. This method is popular because it doesn’t disrupt interior spaces such as homes.
Driven Piles
Foundation piles that are driven into the ground compact and displace soil, greatly increasing their bearing capacity and becoming extremely beneficial when building on granular or silty soils. Furthermore, driven piles are often chosen as foundations for wharf structures or jetties over water as their driving action compacts the soil further and increases bearing capacity significantly. This type of piling is highly advantageous when working on construction sites where heavy machinery may disturb it – ideal for works over water such as wharf structures or jetties.
Driven piles can be manufactured off-site and installed quickly once at their destination. Available in various materials and shapes, driven piles can also be tailored specifically to their target dimensions – meaning fewer piles need be on-site for installation.
Subterranean foundations tend to be less costly than other deep foundations as they don’t require pouring concrete directly into the ground and waiting for excess pore water pressures to subside before starting construction. Furthermore, these foundations boast high lateral and bending resistance.
But their use can have its drawbacks as well, including being noisy during installation and impacting surrounding properties or neighbours. Keller employs latest enclosed hydraulic hammers to minimize noise disturbance.
Needle Piers
The needle pier method of underpinning is used when an existing foundation is in good condition and does not require excavation. It involves drilling holes in walls to install concrete piers which are later covered with more concrete to further stabilize them – this approach is particularly helpful in buildings with weak walls or floors which need support of more weight.
Underpinning may become necessary if your building has experienced changes to the quality of soil that it rests upon due to extensive renovations or natural disasters like earthquakes. Furthermore, expanding load capacities of foundations may also be required if different purposes were originally intended for its design.
Underpinning using the pit technique involves cutting walls into sections 1.2 to 1.5 meters long. A hole is then made above plinth level in each of these segments for inserting needles attached to piles which serve as pile caps; ultimately this system relieves pressure off existing foundations.