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Mine Exploration Forum

Author shallow coal and new houses?
r1xlx

Joined: 25/11/2019

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shallow coal and new houses?
Posted: 25/11/2019 15:14:14
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Two weeks ago I went to see my childhood home as the fields around it had been designated for warehousing.
The adjacent field is now passed for houses and though a few houses were built up to lower room height several had been halted at just lower foundations.
Some excavation about 8-10 feet deep was taking place close to these last projects and on asking why was told that on digging the shallow excavations - UK houses don't have cellars or basements so foundation trenches only go down 2-3 feet - the diggers had found a coal seam and the officials decided that risk of potential house fires getting down into the coal meant the coal needed excavating and thoroughly mixing with the topsoil!
has anyone else ever heard of such a thing?
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Praada

Joined: 03/03/2017
Location: Tibshelf

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shallow coal and new houses?
Posted: 25/11/2019 16:00:37
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Sounds about right, only a council run scheme will overlook these things... there was a recent development on the outer skirts of chesterfield which had reached completion before being condemned and ordered to be demolished. Built over a burning coal seam, carbon monoxide levels within the new unoccupied properties was at harmful levels...

Building over shallow coal seams also increases risk of subsidence and potential for sink holes. There are many properties built over shafts which are pretty much unsellable to the current owners Sad

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r1xlx

Joined: 25/11/2019

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shallow coal and new houses?
Posted: 25/11/2019 16:53:40
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the adjacent field has been opencast in 1947 even though the coal was poor stuff.
adjacent to the site's other side was a closed brickworks quarry I used to explore for fossils and that showed several layers of coal with one good enough for an ex-miner to dig and sell until warned off by the landowner.
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Grout1

Joined: 08/03/2011
Location: West Wales

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shallow coal and new houses?
Posted: 25/11/2019 18:57:31
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Not sure of latest advice, but the NCB/British Coal/Coal Authority recommendation used to be that there had to be at least 1 metre of inert material between an insitu coal seam and the base of any shallow foundation (raft or trench/strip). Piled foundations were allowed to pass through the coal providing they were end bearing and didn't carry loads onto deeper worked seams.

In many instances it was easier to dig the entire seam out under each building footprint to entirely remove the problem. Mini open casts as part of a construction project were not that unusual, particularly if a market could be found for the coal.

Ironically the inert backfill was often PFA (pulverised fuel ash) from coal fired power stations.
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ttxela

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Joined: 04/09/2007
Location: Cambs

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shallow coal and new houses?
Posted: 29/11/2019 11:39:22
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Grout1 wrote:

Not sure of latest advice, but the NCB/British Coal/Coal Authority recommendation used to be that there had to be at least 1 metre of inert material between an insitu coal seam and the base of any shallow foundation (raft or trench/strip). Piled foundations were allowed to pass through the coal providing they were end bearing and didn't carry loads onto deeper worked seams.

In many instances it was easier to dig the entire seam out under each building footprint to entirely remove the problem. Mini open casts as part of a construction project were not that unusual, particularly if a market could be found for the coal.

Ironically the inert backfill was often PFA (pulverised fuel ash) from coal fired power stations.


Interesting, I wouldn't have thought a good coal seam was any less loadbearing than any of the clays and gravels and such that foundations rest on around these parts. Or was the thinking more to preserve the possibility of mining those seams in the future?
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Grout1

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Location: West Wales

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shallow coal and new houses?
Posted: 29/11/2019 12:42:41
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Alex You are quite right in saying that coal has reasonable load bearing properties, but the primary concern is combustion of the coal.

Burning can potentially ignite overlying structures, produce various poisonous gases and substantaialy reduce the bearing capacity of the surrounding ground. There are many examples of reddish burnt shales overlying very shallow coal seams, particularly in the Black Country.

Pit banks with a high coal content were also a common source of burning.

alan
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ttxela

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shallow coal and new houses?
Posted: 29/11/2019 13:41:27
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Ah, I see. I was interested to read Praada's comment about a burning coal seam near Chesterfield. I know coal can burn for extended periods underground and I've seen the pictures of places like Centralia in the USA.

Presumably the situation in Chesterfield is not so obvious from the surface?
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Grout1

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shallow coal and new houses?
Posted: 29/11/2019 14:13:41
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The drilling company I was involved in dealt with a series of shallow fires at Dronfield near Chesterfield through the 80s and 90s. Sometimes it was just being in a geothermal area with the surface warm to touch. At other times they were like Dante's Inferno.

It was too hot to use water, as this just created producer gas (hydrogen) so we had to inject PFA grout to close down all the air routes that fed the fire.

The extreme temperatures trashed all the drill rods and most of the temperature probes!
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droid

Joined: 31/10/2010
Location: Tamworth

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shallow coal and new houses?
Posted: 29/11/2019 15:56:26
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Gob fire?
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Roger L

Joined: 01/06/2010
Location: Huddersfield

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shallow coal and new houses?
Posted: 29/11/2019 16:27:36
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On a housing site in our area it was built on an old shunting yard which served the local mines. The area had been leveled with mine waste. One of the house owners had a fire in their back garden and ignited the ground under. There was a digger digging out and the fire brigade hosing down for ages till it was all put out. On building sites and coal had to be kept covered and not exposed. If it was below the excavation and covered the bearing capacity was adequate for housing.


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