smallblueplanet
|
Re: Silbury Round One
Nov 26, 2005, 22:19
|
"I would be interested to hear if you think that EH have been saying this all along. Or has there been a change in their plans regarding how much original (non-backfill) material will be extracted during tunnelling?"
It seems to me the 'extra tunnelling' has been overstated by some, and the original EH report only ever said extra material (with a figure in cubic meters), might have to removed if it was necessary, in a worse case scenario, in the risk assessment. However it always been EH's declared intent to remove the minimum material necessary to safely backfill the tunnel.
A possible worse case scenario was enlarged upon today, with the example where when the struts of the corroded tunnel supports have to be removed it is possible that a small amount of material where they contact the 'tunnel' might have to be removed as well.
I believe the report is online, someone will have the link I'm sure, but I'll have a looksee too.
|
PeterH
|
Re: Silbury Round One
Nov 26, 2005, 22:24
|
"The report actually says EH want to go into the old tunnels, record the open surfaces and backfill the tunnel with material as close to the original as possible."
Thank you for that.
That was how I read it and that was why I supported it.
So it's all been about mis-communication then?
|
nigelswift
|
Re: Silbury Round One
Nov 26, 2005, 22:24
|
I am very tired, but for the record:
We didn't misinterpret anything. However,
a.>
We did believe EH's Risk Assessment document, (section 8.3.3.3) when it said "For re-entry into the tunnels the amount of mechanical damage is calculated on the basis of tunnel enlargement by 0.2m around the existing roof and sides, along all of the 1849 and 1968-69 tunnelling. The figure here for new damage is 166m3 ".
Today, EH said that's not what they meant "in their wildest dreams" and they were aiming to go in on the basis of zero damage or a minimum amount. We look forward to seeing that in print and for the Risk Assessment to be amended to say that there will be no tunnel enlargement by 0.2m and no consequent loss of 166m3. Indeed, if they can do it we'll be the first to hail the miracle.
b.>
At the other end of the scale, we did believe EH's Risk Assessment document (Section 8.3) which calculated the rate of natural collapse, if nothing was done to be very slow and would take many hundreds of years to take place. From this, we had inferred that it would take 107 years before the equivalent damage to the tunnelling damage would occur. Today, their consultant engineer said he did not know how long the natural process would take and he had been pressured to provide those figures. (Not by us, please note. As if.)
So, we were guilty of believing EH's Risk Assessment. In the event, in the two most crucial matters relating to their intention to tunnel, they say we were quite wrong to do so and we must of course accept their word.
(PS - Pete, I have approached this diligently and to the best of my ability and suspect most people know that and will judge your posting on the basis of what they know of me, and of you).
|
smallblueplanet
|
Re: Silbury Round One
Nov 26, 2005, 22:34
|
"Today, EH said that's not what they meant "in their wildest dreams" and they were aiming to go in on the basis of zero damage or a minimum amount. We look forward to seeing that in print and for the Risk Assessment to be amended to say that there will be no tunnel enlargement by 0.2m and no consequent loss of 166m3. Indeed, if they can do it we'll be the first to hail the miracle."
The Risk Assesment is there to provide a 'worse case' scenario - thats what its done for, it doesn't mean it will happen, but is the WORST that might happen.
"So, we were guilty of believing EH's Risk Assessment. "
No you were guilty of misunderstanding the nature of a Risk Assessment.
|
smallblueplanet
|
Re: Silbury Round One
Nov 26, 2005, 22:35
|
|
I think so yes - read Nigel's post and my reply about Risk Assessments.
|
smallblueplanet
|
Re: Silbury Round One
Nov 26, 2005, 22:40
|
EH site
http://www.english-heritage.org.uk/server/show/category.8613
Conserving Silbury Hill page, the Risk Assessment is called 'Silbury Hill Assessment' (5mb pdf)
(Found in the cellar, in a filing cabinet, in a folder marked....!!!!) ;-)
|
Hob
|
Re: Silbury Round One
Nov 26, 2005, 22:46
|
Ta muchly sbp.
5mb pdf? Ouch-connection-slowness. I think I'll save downloading that for when I'm at work.
|
nigelswift
|
Re: Silbury Round One
Nov 26, 2005, 22:51
|
"No you were guilty of misunderstanding the nature of a Risk Assessment."
Not so.
The Risk Assessment provided two estimates of natural damage progression. One best, one worst. it was therefore not an expression of a worst case scenario. It ewas an assessment of the risk and cannot be explained away otherwise.
We deliberately chose the worst, not the best to arrive at our inference that it would take 107 years before the equivalent of the tunnelling damage happened naturally. Had we chosen the best, i.e. slowest, rate of void migration it would mean it would take a great deal longer than 107 years for the equivalent of the tunnelling damage to occur.
But it matters little. All of the figures have now been disclaimed.
|
Hob
|
Re: Silbury Round One
Nov 26, 2005, 22:57
|
>I am very tired, but for the record:
Thanks for the clarification Nigel. I'm sure you'll offer more detail as and when it's asked for and when you're not knackered.
Get yerself some kip, and dally not with the Saturday evening pseudo-trolling ;)
|
smallblueplanet
|
Re: Silbury Round One
Nov 26, 2005, 23:00
|
|
see, I needn't have bothered...
|
