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Why You Need to Address Subsidence Before It's Too Late

Updated: Nov 14, 2023

Our sister company ABC ANCHORS have been having an influx of underpinning enquiries so we thought a few helpful tips on subsidence may be of use.


Subsidence can cause serious damage to a property if it’s left untreated, which is why it’s so important to address the issue before it’s too late. Subsidence occurs when the ground beneath a property shifts, leading to cracks in walls, uneven floors and doors that don’t open properly. To reduce the risks associated with subsidence, ABC Anchors offers a range of screw pile foundations that can be used to underpin an existing structure and provide a secure foundation for the future. Read on to learn more about subsidence, its causes and how ABC Anchors can help.



subsidence
subsidence

The signs of subsidence

Subsidence is a serious issue that can cause significant damage to your property if left untreated. Therefore, it's important to be aware of the signs of subsidence so you can take action as soon as possible.

One of the main signs of subsidence is the sudden appearance of cracks, especially after a prolonged period of dry weather or drought. These cracks may appear in walls, floors, or even external structures such as driveways. Pay close attention to any cracks that are wider than 3mm, as this could indicate subsidence.

Additionally, subsidence can cause cracks that are not only vertical but also diagonal. These cracks may appear both internally and externally and can vary in size and severity. Keep an eye out for any cracks that seem to be opening and closing throughout different seasons, as this can be a clear indication of subsidence.

Furthermore, subsidence can often result in cracks occurring around weak structural points. This could include areas where extensions or conservatories have been added, as well as around doors and windows. If you notice any cracks developing in these areas, it's important to have them assessed by a professional to determine if subsidence is the underlying cause.

When it comes to addressing subsidence, traditional methods such as underpinning have long been used. However, there is now a more advanced and efficient option available - screw piles. Screw piles are a type of foundation that provide superior stability and can be installed with minimal disruption to your property. These innovative foundations are ideal for addressing subsidence and can provide a long-term solution to ensure the structural integrity of your property.


Causes of subsidence

There are several factors that can contribute to the occurrence of subsidence. One common cause is the absorption of moisture from the soil by trees and shrubs. As these plants extract water from the ground, the groundwater content decreases, causing the soil to shrink. This shrinkage can lead to a loss of support for structures built on top of it.

Another cause of subsidence is the collapsing of drains and culverts. These underground tunnels that transport water can collapse, displacing the soil and altering the water content in the area. This displacement can weaken the foundation of structures and lead to subsidence.

Buried organic material around structural foundations can also be a cause of subsidence. This organic material can either absorb or elevate the soil content, resulting in misplacement or absorption of soil. This change in soil composition can weaken the foundation and cause subsidence.

Improperly compacted ground during construction can also contribute to subsidence. If the ground is not adequately compacted, it can settle unevenly, creating an unequal surface for foundations. This can lead to areas of soil displacement and subsidence.

Finally, the process of leaching can cause subsidence. Leaching refers to the removal of soluble or other constituents from a substance by the action of percolating liquid, such as water. When water flows through cracks in the soil, it can cause the water content to drop and dissolve components in the soil, weakening its stability and resulting in subsidence.

Addressing the underlying causes of subsidence is crucial to prevent further damage to structures. Underpinning and piling foundations, such as screwpiling, can help stabilise the soil and provide a strong support system for buildings.




Traditional methods for addressing subsidence

One of the traditional methods for addressing subsidence is underpinning. Underpinning involves strengthening the existing foundation of a building by adding additional support. This is typically done by excavating underneath the foundation and pouring new concrete footings or piers.

Underpinning can be a labor-intensive and costly process, as it requires extensive excavation work and specialised equipment. It also often requires the building to be temporarily supported during the underpinning process, which can disrupt daily activities and cause inconvenience for occupants.

However, underpinning can be an effective solution for addressing subsidence in certain cases. It provides additional stability to the foundation, redistributing the weight of the building and preventing further sinking or movement. By strengthening the foundation, underpinning can help to prevent further damage to the structure and ensure its long-term stability.

It's important to note that underpinning is not suitable for all types of buildings or soil conditions. The feasibility of underpinning as a solution for subsidence should be assessed by a qualified structural engineer or foundation specialist.

In comparison to other traditional methods such as re-pointing, soil rehydration, and resin injections, underpinning offers a more permanent solution to subsidence. While it may involve more time and cost, it provides a strong foundation for the building and can prevent further damage or sinking in the long run.


The benefits of screwpiling foundations

Screwpiling foundations have become an increasingly popular option for addressing subsidence issues. The process involves digging around the outside of the failed structure to expose the base of the concrete foundation. Pockets are then dug under the foundation at 0.8m-1m centres, and screw piles are installed to torques in excess of 3kNm.

One of the benefits of screwpiling foundations is that jacking plates can be fitted to the piles and lifted using hydraulic jacks, which stabilises the building and, in some cases, lifts it back to its original level. Trenches are then backfilled with soil or type 1 if extra support is required.

Compared to traditional methods, repairing foundations using screw piles is quicker and less disruptive. The process benefits from minimal noise and vibration, which reduces disturbance to occupants of the building and the surrounding environment. Overall, the use of screwpiling foundations is a cost-effective and efficient way to address subsidence issues and stabilise structures for years to come.

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