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The Modern Antiquarian Forum » Silbury Hill » Silbury's structural integrity |
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nigelswift 8112 posts |
Aug 01, 2007, 07:56
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Some lay reactions to Update 11 http://www.english-heritage.org.uk/server/show/nav.17511 In the first half of the tunnel the voiding is said to be no more than 0.5 metres above Atkinson’s steel support arches. However, in two sections this voiding is said to be directly associated with the visible surface slumping uphill from the entrance, which is clearly a lot more than 0.5 metres higher, suggesting (to me at least) that the height of the voiding is only a small part of the story and that the damage and loss of integrity extends in a column above it right to the surface. Hardly a unique observation but it has further significance, see later. Further along the tunnel and within the central chamber there is a very large amount of fallen material and above it “larger” voids and a “significant collapse zone”. How big? It matters, and the public is entitled to know. In fact it’s just about the crux of what the lay public DO want to know about their hill, urgently. So why not tell them? An official estimate or even an official guess would do. One thing that makes me think “big” might mean “very big” is that I’ve heard, rightly or wrongly, that the Atkinson rings far in (of which no account or photographs have been provided) are badly distorted. To me, that suggests massive forces. Confirmation that I have been misinformed would be very helpful. Whatever the answer to that is, an additional official opinion is owed, arising from the fact that the 0.5 metre voids have caused surface disruption far above them. Is there, like there is with the 0.5 metre voids, also a column of damage and loss of integrity extending above these “larger” voids, and if so for how far? “There is no evidence of water cascading through the hill”. Well, not sure anyone ever thought there was (although actually, it might be better news if there was). Instead, “it is more a change of the overall saturation state of the whole mass of chalk”. This sounds worrying, to a lay person anyway. Is this a regular occurrence or unique? If the latter, is there a chance that prolonged saturation of chalk and clay causes irreversible chemical and mechanical changes? And if the latter, we still haven’t heard precisely where this water is thought to have come from and when. There have been tunnels in Silbury for 230 years and worse rainfall in that time. Is the structural integrity of the hill in August 2007 somehow more precarious and the situation more urgent than it has been previously? If so, why? The account so far provided simply doesn’t answer these perfectly natural questions.
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slumpystones 769 posts |
Aug 01, 2007, 17:13
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I wonder if the whole hill has not settled slightly on the outside over the past 40 years anyway. It could be a foot shorter, and I doubt anyone would have noticed. The fact that they say the word 'chamber' a lot now is worrying. That implies a larger area than I thought was dug out in 68-69, which I thought was just a tunnel, like a subterranean archaeologist's trench, rather than an expanding cave, which is what it sounds like now. It really beggars belief that Atkinson was allowed to scar the hill, leave it in disrepair which has further damaged it, and did not even pay his way by publishing anything, and yet is still held up as one of EH's heroes. Says a lot about EH though.
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whipangel 137 posts |
Aug 01, 2007, 19:16
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nigelswift wrote: ...In the first half of the tunnel the voiding is said to be no more than 0.5 metres above Atkinson’s steel support arches... I thought 0.5m was the 'overbreak', the waterlogged crumbly material which 0.5m above would become solid roof again. Not that they should go breaking it off! http://www.english-heritage.org.uk/upload/pdf/Silbury_Hill_web_update_11.pdf nigelswift wrote: ...One thing that makes me think “big” might mean “very big” is that I’ve heard, rightly or wrongly, that the Atkinson rings far in (of which no account or photographs have been provided) are badly distorted. To me, that suggests massive forces. Confirmation that I have been misinformed would be very helpful... I can confirm from my own phone call to EH that mention was made of the Atkinson supports being distorted under the pressures - they were going to have to add their own safety measures as they could no longer rely on these to protect those working on the project. http://www.themodernantiquarian.com/forum/?thread=41033&message=530317
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nigelswift 8112 posts |
Aug 01, 2007, 20:27
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"I thought 0.5m was the 'overbreak', the waterlogged crumbly material which 0.5m above would become solid roof again." You may be right but the wording isn't clear. I took it to me that the overbreak STARTED 0.5 metres above the rings, not that the overbreak was 0.5 metres thick. The latter interpretation seems consistent with the photograph, where there seems tobe a gap of about that size as well as rubble below. In any case, the information that the overbreak terminates at the point there is clean rock is itself confusing since many feet above that we know there is surface settlement. So whilst there may be material above the overbreak that hasn't suffered "in situ" deterioration, it doesn't seem to be the case that it's still in the same situ... Tricky. To work it all out I mean.
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nigelswift 8112 posts |
Aug 01, 2007, 20:30
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Amendment: The FORMER interpretation seems consistent with the photograph.
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tomwatts 376 posts |
Aug 06, 2007, 16:15
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No update 12 yet?
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nigelswift 8112 posts |
Aug 07, 2007, 09:31
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No update 12 yet? Still waiting. One thing (apart from many others) needs an urgent explanation IMO - why is the central shaft being emptied of polystyrene now when it was always scheduled to be done only when the base had been fully stabilised? Has it now been decided that the only way to stabilise the centre is accessing it from the top? Surely not? The only other reason I can think of for going out of sequence is finance. £600K computes at maybe £50K a week so time's money. Is it thought better to utilise the plant and personnel on doing something rather than nothing since they are being paid for? That would make sense, but only if it wasn't a more damaging or less effective solution and wasn't taking an extra risk (for both those involved and the archaeology). Reassurance specifically about that is in EVERYONE'S interest, surely? I'd ask them, but what's the point?
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ocifant 1758 posts |
Aug 07, 2007, 09:47
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..and if they *are* emptying the shaft, given the forecast for more rain later this week, what precautions are being taken to prevent further ingress of water from the top? Questions, questions, and no answers!
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tomwatts 376 posts |
Aug 07, 2007, 10:02
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You'd think a tarpaulin could be found to cover the top.
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Pilgrim 597 posts |
Edited Aug 07, 2007, 10:12
Aug 07, 2007, 10:11
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nigelswift wrote: One thing (apart from many others) needs an urgent explanation IMO - why is the central shaft being emptied of polystyrene now when it was always scheduled to be done only when the base had been fully stabilised? Aye. Especially when we were told that: "The polystyrene in the summit crater would only be replaced with chalk once the voids at the base had been filled or supported, because of the additional weight loading." http://www.britarch.ac.uk/BA/ba80/feat1.shtml Makes you wonder, doesn't it? Peace Pilgrim X
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