A Guide to Underpinning
Introduction
Welcome to our blog post about Underpinning!
Underpinning is a structural engineering works designed to strengthen and stabilize the foundations of a building.
In this article, we will explain the different methods used in underpinning – such as mass concrete underpinning and mini-piled underpinning – and offer considerations you should take into account before undertaking an underpinned project.
Additionally, we will discuss the role of piling when it comes to stabilizing foundations.
Are you ready to learn more about this important process? Read on for everything you need to know about Underpinning!
Methods of Underpinning
There are three main methods of underpinning used in modern construction projects including Mass Concrete Underpinning, Beam and Base Underpinning, and Mini-piled Underpinning.
Mass Concrete Underpinning
Mass concrete underpinning is a reliable and proven method of strengthening existing foundations. Involving careful excavation and pouring of concrete, this technique helps to extend the existing foundation by building a new foundation underneath.
This method of underpinning has been followed for centuries and is suitable for relatively shallow depths – it can be seen as an effective form of preventing settlement or structural damage.
The process involves excavating around the perimeter of the existing foundation before filling with mixed concrete reinforced with steel bars in order to increase its strength – thus stabilizing or reinforcing the old foundational system beneath.
Mass concrete underpinning often seen when there’s insufficient depth in the current footing, yet can also be used if extra space underneath is needed; as it forms an additional base below that which already exists above ground level.
Beam and Base Underpinning
The beam and base method of underpinning is a more advanced technique compared to traditional mass concrete underpinning. This method uses a reinforced concrete beam to support the existing or new foundation.
Reinforcements are placed throughout the length of the foundation, providing additional structural support and boosting its stability. The cantilever pile and beam underpinning is also based on this approach but all work is done from outside the property’s boundary.
Underpinning with beam and base method can be used for both residential and commercial building foundations that have signs of settlement such as cracked walls or uneven floors due to soil movement, load bearing capacity change, corrosion etc. The reinforcement’s provide stiffness, strength in tension and lateral resistance against high loads imposed by construction above ground level which helps preventing further damage or weakening of structures like columns foundations by increasing their carrying capacity significantly.
Mini-piled Underpinning
Mini-piled underpinning is a proven and reliable method for transferring the load from an existing foundation to stable ground. It can be achieved through augering or driving mini piles into the ground.
Auger piling involves sinking short steel tubes into the earth and filling them with high-strength concrete, whilst driven mini piles utilise precast reinforced concrete that is forced down to hard bearing strata.
Commonly used when firm soil layers are located at substantial depths, these methods of underpinning can provide efficient support below superficial soils which may otherwise be inadequate for bearing loads.
The benefits of mini-piling include its accuracy in reaching target objectives relative to cost; increased levels of safety over conventional underpinning techniques due to reduced site disturbance; reduced labour costs relatively low level of disruption caused onsite during installation; minimal ground vibration that helps cut noise pollution, damage and inconvenience for third parties nearby; precise targeting – eliminating ineffective deep excavation works in areas outside the area under repair; plus unrestricted working height limits whereby tall structures can also benefit from this type of procedure where access permits.
Understanding the Role of Piling in Underpinning
Piling is a critical underpinning technique used to strengthen and support the foundation of existing buildings. It involves driving cylindrical piles, such as mini-piles, cantilever pile and beam piles, jack piles or under-reamed piling through predrilled boreholes that reach deep into structural soil layers which they then penetrate or bridge across.
This provides stability for the building by creating an appropriate load transfer path from outside the structure down to bedrock or firm strata below it. Piling has particular advantages over other underpinning methods due its ability to reach further depths than traditional excavations can physically access – with some cases reaching up 500 feet! Mini-piled underpinning also offers non-invasive solutions whereby original structures remain intact from external damage during drilling operation period thanks to modern technologies that are designed to avoid disruption when selecting suitable sites.
Traditional piled foundations typically require more preparation before installation but offer superior strength in soils where native formation might not be adequate enough at shallower levels – therefore it’s essential for engineers to evaluate individual projects thoroughly before opting for the best method of reinforcement that suits each unique situation perfectly.
Finally, it’s important when opting for reinforced concrete piling technique that special careful consideration is taken into account regarding factors such as water pressure and movement loads on varying soil types as this will ultimately affect plans placed onto bearings involved in retaining walls who could potentially collapse without professional advice sought beforehand due incorrect calculations being made early on throughout process stage meaning costly mistakes if processes not followed correctly resulting in considerable delays setback should these scenarios occur.
Considerations for Underpinning
It is important to take into account the potential environmental impacts, financial costs and planning permission requirements before undergoing an underpinning project. Read more to find out all you need to know about this essential construction technique.
Identifying unstable foundations
The signs of unstable foundations can often be seen in walls, floors and even the doors or windows. Piling Enthusiasts should note that cracks in walls are a major indicator of instability as this means the foundation is shifting. Floors may become uneven over time as well, leading to dips and valleys which can indicate an underlying problem. Similarly, stickiness when opening or closing doors and windows usually signals instability because the surrounding foundation has shifted and caused them to move out of alignment with each other. Popping noises coming from either the floor or the wall could also signal that there is a serious issue with an underlying foundation. Other indicators such as water pooling inside, flooding in certain spots due to heavy rains or snow melting on one side of your house are all clear warning signs that point towards possible underpinning requirementry requirements regarding any structural changes made by homeowner must be examined prior to beginning any building project .
Planning permission requirements
When undertaking underpinning work, it is important to understand the need for planning permission and meeting building regulations. The laws governing these will vary according to individual locations, but in general terms, there are exemptions from planning permission regulations when making internal alterations to existing dwellings or where specific undertakings such as house extensions are carried out.
However, approval under building regulations is required for underpinning an existing foundation and any change of use resulting from that may require planning permission. While exceptions exist where some areas do not necessitate obtaining a prior agreement, one should still adhere to the necessary requirements set by local authorities before commencing with any project – failure to comply may risk prosecution and fines.
Listed buildings or properties located in designated areas likely also require approval so determining this beforehand is essential for successful projects as well as compliance with the Construction (Design and Management) Regulations 2015 (CDM).
Cost considerations
When it comes to underpinning projects, cost is a key consideration. The average cost of underpinning a house can range from £6,000 to over £21,000 depending on the size and extent of the work needed.
Different methods such as mass concrete, beam and base, or piling all vary in costs. Piling is the most expensive of these three with an estimated installation rate around £2,600 per meter square.
In addition to this method type expense further costs are associated such as special design considerations and reinforcement should they be required because of soil conditions or lack of space etc; however there are other factors that must also be taken into account like potential planning permission requirements which vary depending on location as well as whether any existing property needs temporarily relocating during works being carried out.
Conclusion
Underpinning is an essential construction technique used to strengthen and stabilize the foundations of a building. It is important to understand that there are different methods, considerations, and issues related to this type of work before undertaking it.
Mass concrete underpinning, beam and base underpinning, and mini-piled underpinning are some common techniques used depending on the existing structure’s needs and problems. In addition, cost considerations must be taken into account prior to starting the project as well as ensuring proper planning permission from local authorities has been granted in some cases.
Finally understanding when underpinning is necessary can help assess what action should be taken for a secure foundation suitable for long term use.
