Sinkholes

What caused sinkholes

The ground under Reading, like much of southern England, is made up of layers of sand and clay sitting on top of chalk. Chalk is unusual because it can slowly dissolve in water. Over time (tens to hundreds of thousands of years) rainwater absorbs carbon dioxide from the atmosphere and soil. This makes the water slightly acidic. As the water seeps into the ground it can gradually eat away at the chalk, creating hidden holes and gaps. Sand and clay from above fill these gaps. This can cause the ground above to cave in. This is called a sinkhole.

Not all ground collapses in Reading are the result of natural geological processes. The area has a legacy of historical chalk mining and clay extraction going back to the early 1800s. These mines become weaker over time, and their roofs can slowly give way until the ground at the surface collapses. This type of collapse is called a crown hole.

Both sinkholes and crown holes can be triggered by:

• water leaking from underground pipes
• heavy rain after a long dry spell
• large amounts of water being added to the ground (for example, from garden soakaways, paddling pools or irrigation systems)
• heavy loads or vibrations on the surface, such as from building work

What happens when they occur?

Sinkholes can be dangerous to the public. They can also damage pipes, cables, roads, and buildings. When one is discovered, the immediate priority is keeping people safe. This can mean fencing off the area, closing roads, supporting nearby buildings or services, and sometimes asking residents to temporarily leave their homes.

Finding out exactly what caused the collapse is also very important. Engineers use boreholes, probes, and specialist scanning equipment to investigate underground and understand the size and cause of the problem. Once they know what they’re dealing with, a tailored repair plan is put together for that specific situation, making sure it is safe, effective, and good value for money.

Who is responsible for the repairs?

This depends on what caused the sinkhole:

• Natural causes — Reading Borough Council is responsible for repairs on public roads and council-owned land. If a sinkhole affects private land, the landowner is responsible.
• A burst or leaking water pipe — Thames Water is responsible for the repair.

Who will keep me informed?

• If the sinkhole is on a public road or council land and was caused naturally, the council will keep local residents updated.
• If a water pipe was to blame, Thames Water will take the lead on communication. The council may also assist where it can.

Contact Thames Water

If you think there is a sinkhole in the road, please call 0118 937 3787 or report the road problem online.