Subsidence on newbuild estate reveals risk of historic mine shafts

Buying a property in an area with historic or current coal mining links is known to present a risk. But serious subsidence on the site of a new housing development on Tyneside has revealed that some historic mine workings have not been recorded.

The Coal Authority is now calling on local planners, surveyors, developers and geotechnical and engineering consultants to take legacy issues into consideration when mapping areas where mining has been carried out.

The Coal Authority wants to ensure legacy issues in mining areas are taken into account by everyone involved in housing so both new and existing properties are safe from subsidence.

Up to 35 newbuild homes on the Bayfield, West Allotment scheme in the north-east have been affected by the discovery of subsidence in July 2016. Several have already been demolished with a further 10 also due to be knocked down.

Authority’s plans didn’t record century-old workings

Experts from the Coal Authority, which is the government body managing the UK’s past coal mining, have since carried out extensive ground investigations on the area, discovering there are coal mine workings to a depth of 30 metres (100ft) that date back more than 120 years but had not been recorded on historical mining plans in the area.

The mining plans for the former colliery that worked that area showed solid coal beneath the ground when, in fact, the coal had been extracted at a rate of between 45 and 50 percent, seriously weakening the supporting pillars.

The subsequent underground collapse has caused a subsidence zone of more than 150m by 70m.

Engineers stabilised the ground

Coal Authority engineers have worked to stabilise the ground, but continual monitoring is required to ensure it remains stable for the redevelopment work that is continuing.

Simon Reed, chief operating officer of the Coal Authority, said: “We have released our initial recommendations to ensure there is awareness of the risks posed by historical coal mining legacy, in light of our findings from this recent subsidence event.

“This was an area of unrecorded mine workings, and caution must be adopted in assuming that the absence of a record means the absence of mining.

“Although our historic plans did not, in this case, reveal the coal workings, they are a vital part of any site assessment prior to development.”