Collapsing mines still a threat - report

SHAUN LOWTHORPE It was a picture which made headlines around the world. But nearly two decades after a number 26 bus fell into a gaping hole in the centre of Norwich caused by a collapsed chalk mine, council chiefs admit old wounds could be reopened in other parts of the city.

SHAUN LOWTHORPE

It was a picture which made headlines around the world. But nearly two decades after a number 26 bus fell into a gaping hole in the centre of Norwich caused by a collapsed chalk mine, council chiefs admit old wounds could be reopened in other parts of the city.

City council documents released under the freedom of information act reveal how the authority kept a top 10 of areas where subsidence has occurred.

They are around Ber Street, Churchill Road, Earlham Road at the city and ring road end, Ketts Hill, Plumstead Estate, Rosary Road, St Stephens Road, Merton Road and Mousehold Street.

It also showed that there were 34 areas around the city where there was known or suspected evidence of old chalk workings or subsidence. In total there were 381 instances of subsidence or settlement - where a site moves downwards because of the weight of whatever is built on top of it, such as a house.

Although the chalk pits blamed for the subsidence in Earlham Road have been filled in with a form of liquid concrete, the city is still riddled with old mines between 12ft and 90ft below the surface. Some date back to the 11th century while others were still in use in the 1800s.

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The mines are attributed to chalk and flint workings started in medieval times to help build the city and its wall.

Carol Marney, Norwich City Council's facilities and buildings maintenance manager, said: “It could happen again. I think it is unlikely and that is where you assess the risk. If it happens it would certainly hit the news and could be catastrophic but the chances of it happening again are very slim.”

Mrs Marney said the Earlham Road chalk mines which caused that road to collapse were filled in back in the 1990s, although other known mines in Rosary Road and Harford Hills had not been.

She added that poor drainage contributed to just as many cases of subsidence as the network of mines and tunnels beneath the city's streets.

“We applied for a grant at the time and back-filled the Earlham Road mines with bound concrete, which is a very runny version of concrete which filled in all the nooks and crannies. That took two to three years on a phased basis.

“We have not done that at the other sites for a number of reasons, one of which is that it costs a lot of money to do and other sites we are aware of have not caused a problem.

“It is a difficult decision, because do you apply for the grant to fill in these mines or do you manage them as instances happen? We decided to manage them as they happen and as a council we do not have a statutory responsibility to fill them in.”

But Mrs Marney said the city council had not kept records since of every instance of subsidence.

“To be honest we do not add much to the record. We are only concerned if it involves a road or one of our properties. I think the only people who might have a record like that is one of the big companies such as May Gurney.”