Underpinning

The fundamentals of underpinning date as far back as the 15^th century. The methods of underpinning have progressed with time. Along with traditional techniques we now have modern alternatives to underpinning that can be completed in one day and without the need for vacating the structure.

Here are some of the underpinning foundation methods:

• Mass concrete underpinning

Mass concrete underpinning is a traditional and most widespread method of underpinning. It involves excavating the ground below the structure in boxed sections and then filling these by pouring concrete. This is carried out from the outside/perimeter of the structure and is suitable for shallow foundations.

• Piled underpinning

Piled underpinning is used when the foundation load needs to be transferred to stable soils at deeper depths as the soil is inadequate to bear the weight of the structure above. Other reasons for piled underpinning include environmental concerns regarding excavated soil or restricted access to the construction site.  Piled underpinning involved the removal of internal floors so that a grid of steel-cased piles could be installed and filled with concrete for the structure to sit on.

• Computer-controlled grouting

Computer controlled grouting uses a multitude of injection ports to deliver high-mobility grout into the ground, under precise computer control, to gently raise the structure in a non-invasive way. Each computer can be programmed to control up to 128 injection ports at once, enabling lifting of very large areas or complex heavy structures. The non-invasive injection ports are only 25mm-40mm in diameter and remain in place for the duration of the work. The self-contained grout batching and control centre is housed within a self-contained unit to minimise onsite footprint and is demountable when necessary to enable access to restricted areas of buildings or infrastructure.

• Resin injection underpinning

High tech, advanced engineered resin injection underpinning is an efficient way to rectify subsidence and re-level structures. Using a process likened to keyhole surgery, an expanding polyurethane resin mix is delivered into the ground via an array of small-bore injection tubes (typically 16mm diameter around the perimeter of the building or 6mm if carried out inside). A chemical reaction and consequent expansion occurs as the components mix together, upon entry to the ground. This reaction and expansion strengthens the ground and the building is returned to level in a controlled manner.