Silbury Hill 180
Image by juswin

Stable door and bolted horses scenario...

When this whole sorry story started some years ago I had some interesting correspondence with the MD of a company which specialises in stabilising structures, buildings, embankments etc. using very sophisticated grouting techniques. We discussed Silbury in theoretical terms and it seems that a pressurised grout could have been employed to fill any voids within the hill. The grout would have been introduced using boreholes little thicker than a finger and would have been almost identical to the original filling, not exactly of course to preserve the difference between old and new. The grout would have been of the same permeability as the main structure of the hill and would not have introduced any excess water which could migrate and destroy lower archaeological remains.
However, EH were implacably opposed to grouting and I don't know if this sort of option was ever discussed with Skansia.
Ain't hindsight wonderful!
Jim.

P.S. When Winchester Cathedral started falling down in the early 20C, a wonderful thing called "The Greathead Grouting Machine" was used to introduce pressurised cement into the crumbling walls. They were stabilised and stand strong to this day. Did EH even consider that techniques may have improved in 100 years?

"However, EH were implacably opposed to grouting and I don't know if this sort of option was ever discussed with Skansia.
Ain't hindsight wonderful!"

Hi Jim
The answer to your question and reasons for not using the drill and fill method are set out in the 2005 Conservation Risk Assessment, freely available on the EH website ( http://www.english-heritage.org.uk/upload/pdf/Risk_assessment052005.pdf) along with a host of other documents. I'm not sure if they discussed it with Skanska but they did manage to employ the expertise of folk such as Emeritus Professor Richard J. Chandler of Imperial College, Fellow of the Royal Academy of Engineering and M. H. Worthington of the Dept of Earth Sciences at Oxford.

As for the poly bags. This fix is supposed to be a permanent fix therefore requiring stability and longevity of materials. Using a natural fibre would surely run the risk of biodegradation before the materials have had a chance to stabilise properly thus running the risk of further collapse. Surely the main aim of the project is to fix the hill permanently and if modern materials are the best for the job then so be it.

I guess I'm setting myself up here to be knocked down but I'm fed up of this constant nit-picking, heresay and rumour. I have tried to keep away from the debates because there seem to be a few here who are working on an agenda that involves constantly beating EH with a big stick for doing exactly what they have been asked to do. I guess I may be in a minority here but I have followed this project with great interest and actually think EH have released an unpresedented amount of freely available material to the public, they have also involved local people and national organisations with an interest in the hill. It's very easy to sit on the side lines and snipe at EH but please show me a project that has done more to keep the public informed.
I would like to congratulate all the folk involved on doing a great job, it looks like the goal of permanent fixing of the hill is in sight and it has been done safely and efficiently.
Well done EH.

cheers
fitz