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Pilgrim

597 posts

Re: Silbury's structural integrity

Aug 15, 2007, 02:34

Littlestone wrote:

English Heritage's Week 13 Update is now available here at http://www.english-heritage.org.uk/server/show/nav.17511

Hi Littlestone,

Hmmmm....

From: “An assessment of the conservation risks and possible responses arising from antiquarian and archaeological investigations deep into the Hill” by Fachtna McAvoy, February 2005:

http://www.english-heritage.org.uk/upload/pdf/Risk_assessment052005.pdf

5.3.1 The observations detailed above allow for a very, very approximate prediction of future collapse rates. If the collapse follows a log-rate process, as shown in Chart 1 below, then a period of 1000 years will be needed for a collapse of 0.5 x cavity diameter. Even if the collapse rate is linear (Chart 2), 300 years are required for a collapse of 1.0 x D.

So, that “very, very approximate” above puts the figure anywhere between the two outliers;

1.The log-rate process of 1,000 years which predicts a rate of migration that gets slower with time:

and

2. The linear-rate process (the worst-case scenario) which calculates out to 300 years.

That’s a mean of 650 years to achieve a collapse of 1.0 x of the Tunnel Diameter, apparently. This is nowhere near the Update 13 prediction of possible visible damage in:

“ a few decades time” and of “at least 1,000 cubic metres”

So we’ve come down from 300 - 1000 years to a “few decades” for damage to appear? In two years of accumulating knowledge? Despite trumpeting Tomography as the be-all-and-end-all?

In 2002, on behalf of the Silbury Hill Project Board, Professor Richard Chandler, - Professor of Geotechnical Engineering at Imperial College London – reported that:

…..“ It appears from the recent investigations …. that the general body of the Hill is otherwise stable”

http://www.english-heritage.org.uk/upload/pdf/silbury_hill_commentary_report.pdf

…you’ll forgive me for being a little unsure as to who to believe in all this.

Peace

Pilgrim

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