What is Subsidence?
Subsidence is a geological condition where the ground level sinks or subsides over time. Commonly detected during a structural survey or geotechnical investigation, the impact of subsidence can be devastating on buildings and structures.
Ranging from cracks in walls, floors and ceiling to structural instability, subsidence can cause major damage to infrastructure such as roads, railways and pipelines, and negatively impact a structure’s aesthetics.
What Causes Subsidence?
Natural Causes of Subsidence
Specific soil types, especially clay, are more prone to subsidence. With shrinking and swell properties, depending on moisture levels, soil can lead to structural instability.
Groundwater extraction can also cause subsidence is excessively pumped, causing the ground to compact and subside.
Rivers and coastal areas can contribute to subsidence due to erosion, in addition to areas in close proximity to large treats that extract water from the soil, causing the ground to dry out and shrink.
Man-Made Subsidence
Underground mining for resources such as coal has historically created voids that can collapse, contributing to subsidence.
Heavy construction, such as large structures and excavating deep foundations, can induce subsidence, in addition to faulty utilities, such as leaking pipes and drains, saturating the soil.
Climate change can also contribute to subsidence, with changes to rainfall patterns and rising temperatures that affect soil moisture.
Signs of Subsidence
There are several indicators to look out for when it comes to subsidence, from structural damage to unexplained changes or below ground drainage problems.
- Cracks: Check for cracks in walls, floors, ceilings and foundations
- Doors & Windows: If doors and windows are difficult to open and close, it could signify there’s an uneven settlement.
- Sloped Floors: Check for any floors which are no longer level.
- Foundation Movement: Any visible signs of foundation movement such as leaning or slanted walls or posts.
What can be done about Subsidence?
Once subsidence is detected, there are several potential actions to take to protect property and structures.
- Foundation Repair: To stabilise a structures and prevent damage, foundations can be structurally repaired.
- Underpinning: Integrating extra support beneath foundations can be used to strengthen structures.
- Grouting: Injecting grout into the ground can help to fill gaps and stabilise soil.
- Soil Replacement: If remedial measures are not effective, it could be necessary to excavate and replace the affected soil (cut and fill analysis).
How to prevent Subsidence?
- Plumbing: Regularly inspect and maintain pipes, particularly antiquated materials, to ensure they’re in a good condition and leak-free.
- Drainage: Ensure gutters, downpipes and drains are free from debris to prevent water from pooling around foundations and contributing to subsidence.
- Trees: Avoid planting trees close to foundations. If unavoidable, regularly check tree roots for any signs of damage.
- Overloading: Ensure structures aren’t exposed to excessive or irregular loads, which can increase the risk of subsidence.
- Expertise: Regularly get structural engineering reports to identify any subsidence or potential risks.