What is a sinkhole? 

A sinkhole is a depression or hole in the ground caused by the collapse of the surface layer. Sinkholes can vary in size, sometimes appearing as small ground depressions or large, wide holes affecting roads or buildings. 

There are two common types of sinkholes: cover-collapse and cover-subsidence. A cover-collapse sinkhole is the more dramatic of the two and occurs when the surface suddenly collapses into a pre-existing cavity. A cover-subsidence sinkhole tends to form gradually. This is where the soil slowly settles into the dissolving rock beneath the surface, often creating a shallow surface depression. 

What causes sinkholes in the UK? 

In the UK, sinkholes are often caused by several factors:

• Impact of water on natural geology – water is the most common cause of sinkholes in the UK. In 90% of cases, water saturating the ground is the main trigger, through what’s known as the karst process. When rainwater absorbs carbon dioxide, it becomes acidic and travels through cracks, dissolving bedrock such as limestone, chalk and gypsum. Although the process can take thousands of years, it can eventually lead to large underground voids. 

• Leaking drains or water pipes – leaking drainage systems can have a significant impact on the development of sinkholes, particularly in dense, urban areas where surface water often accumulates over time in drains and sewers and saturated the surrounding area. Burst water pipes can also wash away the subsoil leading to depressions and sinkholes.   

• Groundwater erosion – groundwater travelling through the subsoil, washes away sediments into the voids, loosening the supporting material beneath the surface.  

• Historic mining or underground cavities – Some houses are built near or above abandoned mines. As these artificial structures age, their structural integrity becomes unstable, causing them to eventually collapse under their own weight.  

• Poorly compacted fill ground – if the soil isn’t strong enough to support the structures above ground, it can settle unevenly and develop voids underground and eventually lead to sinkholes.  

Sinkholes are typically found in The Chilterns, North Downs, Ripon (Yorkshire), southern and north-east England.  

Are sinkholes dangerous? 

Sinkholes can be dangerous, resulting in structural damage, power outages, serious injury and potential groundwater contamination from leaking water or sewage pipes. In 2025, a 65ft sinkhole appeared on Godstone High Street, Surrey which required excavations, road closures, costing over £2.3m in damages.  

It’s worth noting that in most cases, sinkholes don’t develop overnight, they gradually form over months or sometimes years. 

Early warning signs of a sinkhole 

Since movement happens underground, it can be hard to spot a potential sinkhole until a dramatic surface collapse. However, there are some subtle indications to look for. 

Common sinkhole warning signs include:

• New cracks in walls or foundations

• Sloping floors

• Sticking doors or windows

• Circular depressions in gardens

• Cracks appearing in driveways

• Sudden pooling of water

Sinkholes vs subsidence: what’s the difference? 

A sinkhole is a sudden depression or hole formed when the surface collapses into an underground cavity, usually in karst (soluble bedrock) landscapes. Subsidence refers to the gradual sinking of the ground beneath the foundations of a building or structure. Below is a short table highlighting some of the key differences between sinkholes and subsidence: 

Can you fix a sinkhole?

Yes, sinkholes can be fixed, however, the method of repair depends on: 

• Size of the sinkhole

• Soil conditions

• Proximity to buildings

Smaller residential sinkholes are often repaired by filling them with soil, concrete and gravel. Large-scale sinkholes can be assessed with ground improvement techniques by structural engineering experts, such as Mainmark. 

Typical remedial works include: 

• Filling underground voids

• Soil stabilisation

• Strengthening ground beneath foundations

Modern engineering solutions for sinkholes

In some cases, traditional excavation may be required for sinkhole repairs, however, modern ground improvement techniques are often less disruptive. Non-invasive solutions such as resin injection or computer-controlled grouting offers long-term ground improvement with minimal excavation required and less time needed on site. Mainmark’s sinkhole repair solutions not only address the damage resulting from collapse into an underground void but also comprise preventative measures to help avoid further issues in the future.  

How to prevent sinkholes from happening 

The key to preventing sinkholes from occurring is managing drainage systems and maintaining ground stability. Here are some tips to help prevent sinkholes on your property:

1. Repair leaking drains. Fixing broken or leaking pipes stops water from infiltrating the ground and washing away soil.

2. Maintain drainage systems. Make sure gutters are clear and they divert water away from your property foundations, so water doesn’t pool and oversaturate the ground.

3. Monitor ground movement. Look for unusual cracks in walls or driveways and watch for any doors or windows that aren’t closing properly or have become misaligned.

4. Investigate unusual ground depressions early. Check for any small holes or pooling of water in your property. If you spot anything concerning, you should seek professional advice.

It’s important to remember that early intervention can help prevent major structural issues. For further information, contact Mainmark today. 

FAQs

Are sinkholes common in the UK?

Yes, sinkholes are common becoming more common in the UK, especially in areas with soluble bedrock (limestone, chalk or gypsum). They often occur in parts of southern and north-east England, The Chilterns and Dorset. 

What are the early signs of a sinkhole?

Early warning signs to look for include:

• New cracks in walls or foundations

• Sloping floors

• Sticking doors or windows

• Circular depressions in gardens

• Cracks appearing in driveways

• Sudden pooling of water

Can you fix a sinkhole?

Yes, you can fix a sinkhole, but the method or repair depends on the size, soil conditions and proximity to other buildings. Small sinkholes can be filled with soil, gravel and other material to relevel the ground. Large-scale sinkholes require more extensive ground improvement works, such as those provided by Mainmark.  

Who is responsible for fixing sinkholes?

The responsibility of fixing sinkhole depends on the location and cause of the sinkhole: 

• Private land – the homeowner is responsible for repairs if the sinkhole occurs on their property boundary.

• Public roads & pavements – county or unitary council.

• Leaking sewer – local water company.

Are sinkholes dangerous for homes?

Yes, sinkholes are dangerous to homes. They can cause significant structural damage, power outages and safety hazards to occupants.  

What causes sinkholes in the UK?

Sinkholes in the UK are mainly caused by natural dissolution (the dissolving of soluble bedrock such as limestone, chalk or gypsum) by acidic rainwater and groundwater. This process results in underground voids and can remain hidden for years before collapsing. The collapse can be caused by heavy rainfall or flooding, damaged water pipes, or human activity such as mining, construction.

How are sinkholes filled?

Smaller sinkholes are repaired by filling them with compacted soil, gravel and a layer of topsoil. Larger sinkholes are filled with rubble, grout or concrete.