Underpinning is performed when an existing foundation is insufficient to support a building and increase bearing capacity of soil, usually to avoid structural failure and severe damage to structures. This procedure may help preserve structural integrity as well as avoid potential future costs of repair to structures.
There are various kinds of Underpinning Melbourne, from traditional styles to cutting-edge solutions like push piers and steel helical piles.
Mass Concrete
Mass concrete underpinning has traditionally been the go-to underpinning solution, and is still quite prevalent today. This technique involves excavating around existing foundations and filling them with concrete; though disruptive and time consuming, this approach may still work effectively depending on your circumstances.
A concrete beam is then laid across the bases, taking on the weight of the building above it and transferring it deeper into more robust subsoils. This technique may help alleviate issues related to ground heave caused by moisture recovery in clay soils; anti-heave safeguards must be included as part of any underpinning scheme that uses this approach.
The pit method is another traditional approach that works by excavating sections of old foundations until they reach a hard stratum, which is then filled with concrete. As with mass concrete underpinning, its stability must first be assessed prior to excavations starting and propping must continue throughout construction. Anti-heave precautions usually consisting of polythene sheeting or low density polystyrene are usually installed when this approach is employed with shrinkable clay soil.
Mini-Piles
Mini-piling is an economical and quick underpinning method designed for tight conditions. This cost-effective and fast process can strengthen existing foundations without needing to remove or alter current structures, helping builders reduce carbon emissions by using less concrete.
Mini-piling involves various techniques, but one of the most popular involves screwing or drilling a hollow steel shaft into the ground, filling it with grout or concrete and filling its interior space to transfer loads into soil more effectively.
Micro piles, small diameter drilled friction piles, are an increasingly popular solution for underpinning buildings to prevent subsidence issues. These micro piles work by transferring loads through friction into the soil, creating an adhesive effect at where they meet with it – so this process doesn’t require accessing interior spaces like with traditional piles.
Needle-Piles
Pile underpinning methods include the Pile Method. In this approach, steel or concrete piles are drilled into either side of an existing foundation on either side and connected by needles that penetrate walls – an effective strategy when dealing with waterlogged or clayey soil conditions or unstable bearing stratums.
Another variation is the “pile and cantilever needle beam method”, which can be utilized when access to the interior of the property is restricted. This approach works by creating cantilever needle beams on micro piles that protrude from walls while being supported with steel rods.
Injection methods utilizing structural resins are becoming an increasingly popular alternative to the more traditional underpinning techniques. A mixture of resin and hardener injected into the soil penetrates through it, expanding through chemical reaction, filling any crevices or voids, increasing load-bearing capacity and helping prevent further subsidence. This technique can be utilized on many builds.
Tiebacks
Tiebacks, an advanced form of underpinning, consist of high-strength steel strands driven into the soil and grouted. Although this method can be more disruptive than others, tiebacks also offer the additional benefit of providing lateral resistance for existing walls.
Beam and base underpinning involves installing reinforced concrete beams below an existing foundation to redistribute loads to more stable soil layers, providing an economical and adaptable solution for many situations.