A 5m-deep dene hole has appeared in the driveway of a residential property in Upper Basildon, Berkshire.
Source: Peter Brett Associates LLP
The crater measures 10m in diameter and is located about 30m away from where a smaller hole appeared in February 2014 following a period of heavy rain.
The site is located over a 19th century brick factory, which included tunnels running below ground level. Much of the chalk at the site is thought to have been mined and used to create bricks and tiles.
Consultant engineer Clive Edmonds, a partner at Peter Brett Associates which is investigating the incident, explained the likely cause of the collapse is the gradual degradation of the mine tunnel over time.
Often, shaft positions where these brickworks mines were located are not marked on historical maps.
“The residential property was built circa 2000…with an average pile depth of about 11-12m. These problems deeper in the chalk may be down to about 16m,” said Edmonds. “So, potentially, you’ve got weak, voided ground sitting below the level at which the piles stop. So there is a possibility that ground like that may extend beneath the property.”
The hole is being filled with foamed concrete to provide temporary stability until a long-term solution is identified.