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Huge 'sinkhole' emerges in Bexleyheath

Graigwen

Member
This is only about 1000m from my home.

Kent Live link

It is certainly a large collapse, but not a sinkhole. It is on unpromising geology of Eocene sediments near the boundary of the Harwich Formation and Lambeth group. The site used to be part of the grounds of a large house called Marten's Grove, so some buried trace of human activity is possible. I think a small tributary of the River Cray once flowed near here and left some fluvial sands behind. A nearby house, long demolished, did once have an ornamental water feature. Old maps offer no obvious explanation. This area of heathland did have a tradition in the nineteenth century of extremely deep well digging as the water table is a long way down. At the moment the most likely explanation is probably washout from drain or water mains failure.

I asked some locals whether they thought this could be part of a cave system larger than Ogof Draenen. Their replies were:

"Could be."

"It is huge."

"I dunno."

"What is a Dry Nan?"


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Graigwen

Member
I might have been a bit unduly dismissive of this site.

There are old denholes recorded at the back of the Crayford gasworks only a few hundred metres away, and even closer in Braeside Crescent. These go down through surface deposits to reach the chalk at some depth.

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Graigwen

Member
Having now had the chance to examine the site on the ground, I think there is a fair chance it is an old denehole. It is being guarded by Thames Water as a water main was fractured and there is also a sewage leak. The employees on site could not give any information about telemetry data, this would have confirmed whether water loss preceded collapse, as wash out is the other alternative to a denehole collapse. (In 2018 Welsh Water telemetry data enabled the exact time a water main fractured, lubricating the material involved in the collapse of Vicarage Lane, Abersychan several hours later, to be established. This made interpretation of the incident more simple.)

The motor bike that fell into the hole is still there. the circumstances in which this happened have already become the subject of several stories among locals. One involves the shocked rider clambering out of the hole and calling for a taxi.

Undisturbed layers of sediment can be seen in several sides of the hole. The material as expected, looks very weak. This collapse is about 230m from the gas works denehole and 145m from the Braeside Crescent denehole, roughly in between them. I remember Harry Pearman (Chelsea SS) telling me in 1967 that the gas works denehole had been filled in.

Spurrel, a local historian, wrote in 1881 :
Spurrel 1881 extract.JPG
The Elms was a large house, long demolished, on the other side of Watling Street about 500m from this collapse. By co-incidence this house was the home of my late wife's great great grandmother in about 1844.

Martens Ave collapse 2.jpg
 

Graigwen

Member
Video here. (Sky news)

It has taken 24 hours for competing stories to become established. The one above is the most sensational and has got most newspaper coverage. Yesterday several locals told me that it was a pathetic attempt to dispose of a stolen bike. I have no idea what the truth is.

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Cantclimbtom

Active member
I might have been a bit unduly dismissive of this site.

There are old denholes recorded at the back of the Crayford gasworks only a few hundred metres away, and even closer in Braeside Crescent. These go down through surface deposits to reach the chalk at some depth.

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Yes, definitely Denhole is a prime suspect - we need KURG to take a looksee for us. I did a lot of research about Deneholes in Bexley, Bexleyheath, Darenth and so forth as part of research for the analogous ones in South West Essex. Just down the road from Bexleyheath and unfortunately there is a big cluster of them in what was historically Baldwyn's shooting estate, which is now a housing estate, and unfortunately I'm expecting sooner or later to see Bexley in the news just like Bexleyheath above. I don't yet know where this hole is in Bexleyheath, but out of interest the neighbouring Bexley situation looks like the map below. I did spend some time trying to find an open example but I believe all the ones round there (with exception of Darenth) are closed waiting for collapses to reveal them... maybe I better get a rope and drive down to Bexleyheath pronto ;) My prediction is that we'll see one open in the purple circle in map below next time after the next time we have prolonged season of unusually heavy rain

Bexleyheath.jpg


And I *imagine* the same is happening in Bexleyheath as above for Bexley and the cause of the hole in the news article.
Although the link below is South Essex (not Bexley or Kent), it is pretty much the same as described and very similar geology. This will give you some background on Deneholes and what they are/aren't and why they are there (probably...). I hope this will make things make more sense

Enjoy...
 

Cantclimbtom

Active member
Call me pedantic... but should this be moved to the mining exploring forum (unless it's proven not to be mining (Denehole) related).
We need more threads and traffic over there and having this in the caving section strikes me as downright theft :ROFLMAO:
 

Graigwen

Member
Yes, definitely Denhole is a prime suspect - we need KURG to take a looksee for us. I did a lot of research about Deneholes in Bexley, Bexleyheath, Darenth and so forth as part of research for the analogous ones in South West Essex. Just down the road from Bexleyheath and unfortunately there is a big cluster of them in what was historically Baldwyn's shooting estate, which is now a housing estate, and unfortunately I'm expecting sooner or later to see Bexley in the news just like Bexleyheath above. I don't yet know where this hole is in Bexleyheath, but out of interest the neighbouring Bexley situation looks like the map below. I did spend some time trying to find an open example but I believe all the ones round there (with exception of Darenth) are closed waiting for collapses to reveal them... maybe I better get a rope and drive down to Bexleyheath pronto ;) My prediction is that we'll see one open in the purple circle in map below next time after the next time we have prolonged season of unusually heavy rain

View attachment 13451

And I *imagine* the same is happening in Bexleyheath as above for Bexley and the cause of the hole in the news article.
Although the link below is South Essex (not Bexley or Kent), it is pretty much the same as described and very similar geology. This will give you some background on Deneholes and what they are/aren't and why they are there (probably...). I hope this will make things make more sense

Enjoy...
I went down a few of the ones near Coldblow and Stankey Wood (which we always called Sankey Wood) when I was a kid. Even in the late 50s/early 60s most were blocked. Usually it was ones with cut footholds - all we had to help was a clothes line. Did you see the Fæsten Dic while you were in Joydens Wood?

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Graigwen

Member
Call me pedantic... but should this be moved to the mining exploring forum (unless it's proven not to be mining (Denehole) related).
We need more threads and traffic over there and having this in the caving section strikes me as downright theft :ROFLMAO:
It is not actually proven to be a mine....yet.

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Cantclimbtom

Active member
I went down a few of the ones near Coldblow and Stankey Wood (which we always called Sankey Wood) when I was a kid. Even in the late 50s/early 60s most were blocked. Usually it was ones with cut footholds - all we had to help was a clothes line. Did you see the Fæsten Dic while you were in Joydens Wood?

.
I was researching remotely Google earth, googling etc + asking an old mate who lives thataway to nosy about for me. I haven't been there myself, at least not recently, last time was a long long while ago.. awful.. I hired a horse from Mount Mascal stables and rode, now I'm no horseman and the 🤬nag would jump/startle and try to bolt if it saw a dog -- which was all the time.
I spent the whole time reigning it in and trying to stay on, it was hard work and I was glad to return it, I might have ridden through the middle of Fæsten Dic and not noticed, but I didn't let it get the better of me. Anyhow, "happy" memories 😨
I was up for an on foot trip but he was pretty sure that none were still open, might still have a walk about if in those parts soon, you never know... maybe ones is open? Nice area!
 

Graigwen

Member
Two months have passed while Bexley Council argue with Thames Water about responsibility. Here is a photo from yesterday. The road is still closed, although the hole has been filled in. Locals have been kept in the dark. Apparently it is promised that the road will reopened this week.

Martens Ave 21 August 2022 2.jpg
 

mikem

Well-known member
To be fair, the council did post this shortly after it happened (good pic of damage too):
"The Council’s engineers currently estimate that it will take about six weeks to clear the site, fill the hole, repair Thames Water’s pipes below the ground and then re-lay the road surface and footpaths.

They have employed specialist companies to carry out a ground survey of the area to identify any other locations of concern."
 

Keris82

Member
Yes, definitely Denhole is a prime suspect - we need KURG to take a looksee for us. I did a lot of research about Deneholes in Bexley, Bexleyheath, Darenth and so forth as part of research for the analogous ones in South West Essex. Just down the road from Bexleyheath and unfortunately there is a big cluster of them in what was historically Baldwyn's shooting estate, which is now a housing estate, and unfortunately I'm expecting sooner or later to see Bexley in the news just like Bexleyheath above. I don't yet know where this hole is in Bexleyheath, but out of interest the neighbouring Bexley situation looks like the map below. I did spend some time trying to find an open example but I believe all the ones round there (with exception of Darenth) are closed waiting for collapses to reveal them... maybe I better get a rope and drive down to Bexleyheath pronto ;) My prediction is that we'll see one open in the purple circle in map below next time after the next time we have prolonged season of unusually heavy rain

View attachment 13451

And I *imagine* the same is happening in Bexleyheath as above for Bexley and the cause of the hole in the news article.
Although the link below is South Essex (not Bexley or Kent), it is pretty much the same as described and very similar geology. This will give you some background on Deneholes and what they are/aren't and why they are there (probably...). I hope this will make things make more sense

Enjoy...
There's already a lot of dene holes around this area. We found a large one in joydens wood. It was fenced off with a tall metal fence and we would have been interested to take a deeper look but it was full of dog poo bags 🤮
 

Graigwen

Member
As I posted earlier, it is very close to already known deneholes.

"This collapse is about 230m from the gas works denehole and 145m from the Braeside Crescent denehole, roughly in between them."

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tomferry

Active member
Deneholes look so similar to the bell pit design from images I have seen by googling them, I assume a sink hole would be much harder to fill than a denehole. A denehole appears to be a single chamber, I assume a sink hole would be a network of stuff so much harder to fill !
 

Cantclimbtom

Active member
Deneholes look so similar to the bell pit design from images I have seen by googling them, I assume a sink hole would be much harder to fill than a denehole. A denehole appears to be a single chamber, I assume a sink hole would be a network of stuff so much harder to fill !
I think a bell pit is exactly that, a bottle/bell shape hole. Shouldn't be too hard to fill just drop some hard setting slurry down it.

But the distinctive feature of Dene holes (although there are several designs/variations) are that it's a shaft and at the bottom then there are chambers laid out radiating from the shaft a bit like a double clover leaf shape. In some cases connecting to other Dene holes accidentally, or in case of Thurrock intentionally (don't know if that is original construction or more modern digging?). That would be much harder to fill without leaving voids.

Nowadays the open ones are gradually filled in. People seem to find them irresistible to throw dog waste bags over the fence. How public spirited of them :(
 

Graigwen

Member
I drove past the site yesterday and it looks as if another layer has been added to the surface.

It might actually be finished today I guess.
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tomferry

Active member
Yea if it connected to others it would certainly need massive amounts of vibrators to get into all the pockets , main issue I think they would face would be not being able to go inside ! In the ideal world you would enter and build walls and do it in sections and then sort of shim pack the very top like you do when under pinning.
 
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