Underpinning is the process by which the foundation of a building is strengthened to ensure that it is completely secure. Underpinning can be conducted through a variety of different methods, each with their own characteristics. This guide will help you to understand the key differences between each method to help you decide which will be best suited to your building project.
Perhaps the most traditional underpinning method is the pit method, otherwise known as the mass concrete underpinning method. This works by splitting the full length of the foundation that is going to be underpinner into portions of 1.2 to 1.5 metres lengthwise. First, a hole is drilled into the wall above the plinth level, and a needle made of wood or steel is put into the hole. Bearing plates work to hold the brickwork above the needle, and the needle is supported by wooden blocks and screw jacks on both sides of the wall.
Next, a pit is dug up to the required level of the new foundation, which is then poured into the pit. This is repeated until all of the sections have been filled.
Angle piling is considered to be a slightly more efficient alternative to standard underpinning procedures. It doesn’t require a large amount of excavation work, so it doesn’t cause wide-scale disruption. Through the angle piling method, the walls are reinforced with concrete piles that are paired at opposing angles of about a 1 to 2 metre distance away. The floor also gets pre-drilled with an air-flushed percussion auger. Once this step is completed, a steel liner is then driven into the poor grade/subsoil through the drill hole until it hits the hard stratum.
Applying angle piling on both sides of a wall can be quite complicated in certain situations. When considering the state of the subsoil, it can sometimes be improved by following this method on one side of the wall only. Piles can also be set closer together for improved stability.
In order for this method to work, the wall should be separated into legs for bays, and each bay must be addressed separately to avoid any fractures, damage or settlement. There are several factors that influence leg and bay length, including the length of the wall, the bearing capacity, the type of soil and the strength and stability of the wall.
Depending on the type of project you are undertaking, there are a few methods that may be more effective. For a less intrusive procedure, for example, a single concrete beam could be inserted beneath the existing foundation. Jet grouting – where resin or another chemical component is injected into the ground, filling any voids and providing additional support – also benefits from requiring little to no excavation.
If you’re unsure about where to start with underpinning , Below Ground is a piling, underpinning and foundation contractor with over 25 years of industry experience. Our knowledgeable team is always happy to answer any queries you might have, and will talk you through the various underpinning methods that would be best suited to your construction project. Please get in touch for more information.