Sinkhole mayhem – what do we know about the A1 sinkhole?
Sinkholes… They certainly are becoming more frequent around the country but what causes them and is there anything we can do to predict or prevent further holes appearing?
Essentially, a sinkhole is a hole in the ground created by erosion and the drainage of water. They can vary from just a few feet across up to large enough to swallow whole buildings. Although true sinkholes are the result of natural processes (dissolution) they can be triggered by a range of human activities like vibration or drilling work that affects the water table level. Others (crown holes) are caused by the collapse of abandoned mines. Unfortunately, it is not possible to pinpoint the exact location of potential sinkholes nor predict what the timescale might be – however, it is possible to be aware of indicators of higher risk areas by taking into account the risk zones drawn up by BGS (British Geological Survey) which is based on the geology i.e. vulnerable soil, rock types and areas where there may be shallow mine workings in coal or other minerals. These areas could be seen as more vulnerable and a collapse could be triggered by factors such as increased rainfall through climate change, by changing the underground water regime, loading or disturbing the ground by drilling, building works or altering drainage.
Recently, a major 3m deep hole appeared on the busy northbound A1 near Newcastle and Gateshead between junctions 67 and 68 causing rush-hour congestion, we got our FCI experts on the case to see what could have potentially caused the road to collapse.
Rob Keskeys, our product specialist looked into the affected area using an historical map and revealed that the whole area is made up of closely spaced coal mine workings. The historical map laid over the aerial image (shown below) shows an old quarry area just to the west of the road as it straightens up to head north. Our data shows a pit located just to the south east of the quarry (circled red on the image below), which looks like it’s on the A1 and interestingly has been listed as deep coal workings. Although the cause of the hole could have been a number of things from a sewer collapse to crown holes, the evidence strongly points towards an old coal mine being the prime suspect.
We spoke to Dr Clive Edmonds, a specialist in Geotechnics and Geohazards and a partner at Peter Brett Associates LLP which provides risk area data to FCI environmental reports. He said “The crater in the A1 is typical of many old mining areas where the mines are rapidly degrading and are prone to sudden collapse as the void migrates to the surface – potentially triggered by traffic vibration, loading and rainfall. A similar event occurred within the central reservation of the M2 motorway in February 2014.”
Luckily, commuters will be happy to know that the A1 has now fully reopened after repairs on the carriageway were completed overnight. We’re sure motorists are very happy about this!
Other sinkholes that have hit the news in the last few weeks include the giant 30ft wide and deep sinkhole which opened up just metres from residential homes at the Towy View Park in South Wales, this was a result of homes built on top of an old lead mine. Another sinkhole appeared on farmland close to the Carrickfergus Forest in Northern Ireland, the land owner said he was worried that it might have been a result of a nearby oil drill site which may have disturbed the ground.
Did you know…? One of the biggest sinkholes in Europe is approximately 80 metres (260ft) in diameter and 30 metres (98ft) deep and is located at Pouldergaderry in Ireland. It’s even got mature trees growing on the floor of the hole! An even larger one called Culpeppers Dish is about 90 metres across and 40 metres deep and is located upon the chalk in Dorset near Briantspuddle – again complete with trees!
For more info on the A1 sinkhole, click here.