Imminent completion had me wondering yesterday about what would happen when all filling was complete, today my wondering’s over but my fears remain.

All repair works to summit, tunnels and sides are now complete, the sides repairs will be seeded and Skanska have begun to clear up the Hill by removing the entrance way they installed.

A fence has been erected (photo figure 2) around the summit infill area, so that it can be ‘allowed to completely dry out safely’.

I’m impressed that the Hill has been repaired. There were times its future didn’t look good at all, and even the recent updates reported new surface voids and collapse problems.

Given the weather so far this year and the wet forecast for Summer, I almost wish that they were keeping a small presence there until the next few months show the site to be truly safe and sound.

Update 27 reports the seasonal shutdown in December/January, and three surface collapses, each up to 1.5m deep. The accompanying photograph is wonderfully captioned ‘ Hill side collapse features’. Archaeological recording will take place prior to backfilling.

Update 28 reports on more bad weather, resultant collapses and tunnel blocking. The ditch flooded (as sight I have yet to enjoy) so the monorail had to be relocated. Skanska and EH are confident that settlement from the Hill void may now be complete.

Update 29 charts backfilling continuance dogged by collapses ‘in the outer sections of the Atkinson tunnel’ related to January’s weather. Backfilling of East/West lateral tunnels completed 8th February 2008. The central Atkinson tunnel is now also filled, as have the Silbury 1 excavated areas: ‘have been filled with a combination of crushed chalk installed by hand and chalk paste which does not include any lime or other materials, thus providing an ncontaminated environment with the aim of ensuring the long term preservation of the central organic material’, good to know. The rest of this update examines the process of backfill into the ‘new’ tunnel, with photographs.

Update 30 reports on void fill completion and removal of Atkinson’s concrete portal (off to the museum with you!) . The entrance is carefully filled with a ‘large bank of chalk’ and then the void behind filled with paste. The total tonnage of chalk used to fill the tunnels is reported in this update, and the confidence that ‘all of the known voids have been infilled as well as practically possible to do with material of the same composition as the original hill construction’. The summit void fill begins (photos).

Update 31 is the latest, and reports on near completion of the summit void, with ‘crushed chalk…hauled to the top of the hill using the monorail’ as the final layer over the pumped chalk. Hill side works have begun – Figures 2 and 3 show a ‘3t 360 excavator’ removing the stacks following the creation of a’stable slope’ to facilitate it, and a dumper bringing chalk up for the infill. Stripping the side of the Hill to create this slope puts the odd evening trespasser into perspective on this SSSI, but I suppose it has to be done somehow. Archaeological recording of the surface craters has taken place.

That’s where we stand. The number of reported collapses during the backfill are a little worrying, but now there’s nowhere for collapsed material to go, and the unstable sections filled from above we can only hope that as her overhaul nears completion she’s now capable of shrugging off any weather the rest of the year may bring.

English Heritage updates on Silbury Hill

All the indications are that EH will not be updating the public on matters from now on – which given the remaining 1968 tunnel entrance and doors, and the electrical probe installation ( and the heated debate over the time capsule)- fails to recognize that public interest is for the Hill’s welfare as much as it’s re-discovery.

It is also heartening to read that none of the experts or groups involve think that Silbury is in direct catastrophic danger, however it’s clear that public interest in the Hill is influencing the release of information:

“To put this void into context, the volume of the manmade
portion of Silbury Hill is estimated to be in the
order of 234,000 cubic metres of chalk rubble. The
central collapse volume is 125 cubic metres, which as a
volumetric ratio is 0.05% of the volume of the hill.
Thus, from a structural perspective, this void constitute
a very minor volume compared with the whole
structure, and both Skanska and independent
geotechnical experts have concluded that there is
absolutely no risk to the overall structure of Silbury
Hill, in terms of major collapse or any implied or
rumoured ‘implosion’.”

Some of the report’s contents could have been released earlier, and perhaps minimised the rumour. It’s good to know she’s not in bad shape, there’ll probably be more to worry about once all the diggers, the portakabins and the fences are gone.

On the 26th, English Heritage halted all works, due to instability above the Atkinson Chamber (the improperly refilled 1968 televised intrusion from the roadside), “which has also been exacerbated by the volume of rainfall”.

Posting a statement to their weekly updates section, there was no word on just how much instability there was, and rumours began to spread about a ‘catastrophic internal collapse’.

A local radio station picked it up, but on ringing the BBC in the region on Thursday evening, they’d had no word. By morning, and another phone call, BBC Radio Wiltshire we’re investigating and had a statement from English Heritage. Sadly I missed this, and ended up ringing English Heritage myself.

All work had stopped because Skanska’s original (and admirable) plan of not introducing any more modern intrusion than was necessary by using Atkinson’s own tunnel supports was no longer workable. There had been an internal collapse in the earlier, vertical shaft (re-opened in 2001 and had been temporarily filled) and the surface of these tunnels was now so waterlogged that there was lots of loose material. Safety concerns preventing access, it was impossible to judge the extent of the danger the Hill was in.

A new working plan had already been devised by Rob Harding by Friday when I spoke to him (I gather he gave the statement to the BBC, but was more than willing to give me all the detail on the situation again when I rang, for which I am thoroughly grateful), and it is hoped this can begin to be implemented next week. The costs and duration much expanded by the additional works.

More information can be found at the Excavation diary on the Avebury Lodge website, EH’s own pages, and many of the news agencies have now picked up on this story, The BBC posted this on Friday after the interviews and the Guardian covered it on the same day.

Silbury still stands and fingers-crossed the rains will abate and work will continue, The situation for the Dinedor Serpent is not so certain.

Silbury Hill Update 05 (PDF)