SILBURY HILL UPDATE 1st June 2006

As you may have seen in the Press English Heritage recently announced the appointment of engineering contractor Skanska to take forward the next stage of repair work to Silbury Hill. Skanska will now begin working with English Heritage to draw up detailed repair plans for the Hill.

The repairs will tackle the damage caused to the Hill after a collapse of the infilling to a shaft at the top of the Hill in 2000. The brief for engineers was prepared by English Heritage and a team of expert advisors, and its aim is to find the best method for returning the Hill to its original state and preserving its long term stability. As well as permanently infilling the collapse to the head of the shaft, the works will involve the thorough backfilling of tunnels at the base of the hill, and repair the slumping on the sides of the Hill. The chosen method for backfilling is to re-enter the Hill through the 1968 Atkinson tunnel to its centre.

Skanska won the work after presenting a detailed submission covering practical design and construction techniques, risk management plans and an approach integrating the archaeological and construction elements of the project. The firm proposes using the Atkinson's original supports and additional temporary props to keep disturbance of the Hill's archaeology to an absolute minimum. Archaeologists will be working alongside the contactors to make a record of the internal structure of the Hill and take samples to recover palaeoenvironmental evidence and material for radiocarbon dating.

Skanska has worked with English Heritage on Silbury Hill in the past, contributing to the specialist stability survey work carried out on the Hill since 2000. The firm was selected for this phase of the work because the project board felt their submission best demonstrated how the brief could be safely met with the least risk of disruption to the Hill's archaeology and within a realistic timeframe and budget.

The development of detailed repair plans is now expected to take six months. Depending on the outcome of this development work, English Heritage hopes to commission the full repairs by Skanska and announce the start of repair work in Spring 2007. The repair project will be accompanied by a programme of archaeological investigation, recording and sampling.

We are working on the outreach and publicity programme. The relevant pages on the EH website will soon be up-dated which you will be able to access for future information.

Yours sincerely

(Signed)

Dr Robert H Bewley

Planning & Development Regional Director SW

English Heritage

Bid to save Silbury Hill could cost £600,000

Thursday 1st Dec 2005.

THE collapse of infill at Silbury Hill has happened before and will happen again unless urgent action is taken to stabilise it, a meeting in Devizes heard on Saturday.

English Heritage had called the ticket-only meeting to discuss its preferred option for the future of Silbury Hill, the most ancient man-made structure in northern Europe.

It wants to enter the tunnel dug by a team of archaeologists in 1968 and back-fill it with chalk, also filling in the voids created during the various excavations of the mound since the 1776 tomb-raiding exploits of the Duke of Northumberland.

Amanda Chadburn, one of the English Heritage team who has been investigating the current state of the hill, said the appearance of the hole at the top of the mound in May 2000 had come as a shock to archaeologists.

There had been a further collapse in December 2000 after which the hole was given a metal cap supported by scaffolding. The hole is now temporarily filled with enormous expanded polystyrene blocks.

It had been well known that the Duke of Northumberland, searching for the legendary golden statue of King Zil reputed to be buried in the mound, had employed miners to dig a shaft straight down through the centre of the hill and had refilled it with branches topped with a chalk plug.

The situation was made worse by a subsequent tunnel dug into the side of the hill by workmen hired by Dean Merewether in 1849.

But during her investigations through the archives of various museums in the county, Ms Chadburn had discovered that the collapse of the central shaft had happened before.

She showed an aerial photograph taken in 1925 clearly showing a hole at the top of Silbury Hill, similar to the one that opened up in 2000.

She had also found letters referring to this hole that was eventually filled in by the Ministry of Works in 1936.

Archaeologist Fachtna McAvoy said boreholes were driven into the hill by English Heritage to carry out a seismic survey of its interior.

Cameras were lowered down these holes and archaeologists were appalled to see huge voids that had appeared in the 1968 Atkinson tunnel that was supposed to have been properly backfilled.

Bob Bewley, regional director of English Heritage, said it was important to enter the tunnels and make sure that all voids were properly filled to prevent any further collapses within the ancient monument.

But Nigel Swift, for the protest group Heritage Action, urged English Heritage to think again.

He told the meeting: "Re-tunnelling will destroy a lot of archaeology so we would have to have a lot of confidence that English Heritage knows what it is doing. We see no confidence in it."

He said English Heritage's own figures showed the damage caused by tunnelling would amount to 166 cubic metres and a better option would be grouting the voids from outside the hill by pumping in filler material.

Professor Chandler from Imperial College, London, said the hill was in no immediate danger.

He said: "The hill looks not too different from the way it looked when it was completed. Rabbits and badgers are doing more damage than anything else done to it over the centuries."

Mr Bewley said that invitations to tender were going out to prospective contractors over the next few weeks and the work was unlikely to be complete before 2007.

The cost has not been finalised but it is thought to be in the region of £600,000.

EXPERTS have come up with a plan to save ancient landmark Silbury Hill from collapsing in on itself ­
but they need up to £600,000 to carry it out.
English Heritage has reached a decision on which option to take to stabilise the ancient monument,
the largest prehistoric man-made construction in Europe, and guarantee its continued existence for centuries to come.
It has chosen to re-enter Silbury Hill through the tunnel dug to its centre in 1968,
the subject of a BBC film made by Magnus Magnusson at the time.
The existing material that has been used to backfill the various excavations that have taken place over the last 200 years
or so will be removed and replaced with chalk to the same density as the surrounding mound material.
The temporary capping at the top of the shaft dug into the hill in the 18th century, which is composed of expanded polystyrene,
will be removed and it, too, replaced with chalk.
Bob Bewley, south west regional director for English Heritage, said: "The tunnels have never presented the major problem.
Most of the subsidence is as a result of the shaft that was dug by the Duke of Northumberland's men in
1776 straight down through the centre of the monument in the search for gold.
"They found no gold at the base but it has left us with major headaches as it has never been satisfactorily filled in and is the
cause of all the major subsidence that has threatened Silbury Hill."
Mr Bewley and his colleagues are confident that recent work to stabilise the monument will keep it safe in the short term
while arrangements are made to undertake the massive effort to complete the repairs.
It has already been five years since a massive hole opened up at the top of Silbury Hill,
which was exclusively reported by the Gazette at the time.
But Mr Bewley explained that rescuing a 4,700-year-old construction from dereliction is no short-term matter.
He said: "We have not taken the quick and easy fix but have tried to understand what is happening inside the hill,
which is why is has taken so long to come up with our decision.
"When we are finished the hill will hopefully not require any further attentions for hundreds of years,
although we will be monitoring it regularly."
A project board meeting is due to be held in October when a decision will be taken to put the work out to tender.
Mr Bewley said: "We hope to find the right contractor in this financial year and the work will be started in either the
next financial year or the following one.
"The biggest thing will be finding the money for the work. We reckon it is going to cost in the region of £500,000 or £600,000
 and we are going to have to find that money from somewhere.
"Some of that may come from commercial sponsorship. Large companies and other organisations may be pleased to be
involved with this kind of project.
"It is a World Heritage Site and will attract publicity from all over the world."

Update on the future of Silbury Hill
from http://www.english-heritage.org.uk/server/show/nav.8820
English Heritage has announced the latest stage in the process to repair and preserve Silbury Hill,
the largest Neolithic construction of its type in Europe, and part of the ancient landscape of Avebury,
a World Heritage Site.  Since the collapse in 2000 of infilling to a shaft at the top of the Hill,
English Heritage along with a team of expert external advisors, has carried out extensive investigations into the
condition of the Hill and research as to the best way forward to preserve its long term stability.
This work outlined a number of options for the future of the Hill, one of which has now been selected by
English Heritage for further exploration and feasibility studies.
English Heritage consulted with a wide group of interested parties before the decision  was taken, and presented three
main options for discussion at a seminar for local and national archaeology experts in
September 2004. The option chosen is to re-enter Silbury Hill via the tunnel dug to its centre in 1968, and then remove
existing collapse and inadequate backfill in the tunnel, before properly backfilling it. The tunnel and other voids within
the Hill would be filled with chalk to the same density as the surrounding mound material. The work of backfilling
would take place backwards from the centre of the Hill, and enable contractors to remove any temporary supports
left after previous excavations. The work would be accompanied by an archaeological investigation programme which
 would fully record all the parts of the Hill which are exposed again and enhance our knowledge of its construction.
 Following this work, the temporary capping to the top of the shaft at the summit of the Hill would be replaced with chalk,
 and a monitoring programme put in place to assess any settlement of the of the Hill in the future. The benefit of this way
forward is that it will return the Hill to as near its original state as can be practicably achieved. It will prevent further damage
to the Hill from upward migration of existing cavities. It will preserve the long term stability of the Hill, whilst minimising
further damage to its unique archaeology. In its work to date on the Hill, English Heritage surveys have confirmed
that the overall structure of the mound is stable, although there are localised pockets of instability arising from the
presence of the shaft dug in 1776 and the inadequate backfilling of the tunnels to the centre of the Hill, which were
dug in 1849 and 1968/9. What happens next? English Heritage is drawing up a detailed brief for contractors, who
will be asked to demonstrate how they would execute the proposed option whilst fulfilling the overall objectives of
the project.  English Heritage will assess their submissions before making a final decision on whether to go
ahead with the work.
At the same time, English Heritage will be looking into funding options for the project.

25th February 2003

 English Heritage is now planning to investigate the area of the previously collapsed shaft. As part of this assessment EH intend to test the
 consistency of the backfilling in the lower part of the shaft by drilling a borehole through it from the top. Another borehole will be drilled nearby
 as a control. The information gathered will help EH design long-term remedial work.

 The work is due to start during the first week of March 2003 and to be completed on site on 26 March 2003.

More morons climbing the hill to view the
No War banner.
(EH removed the banner on 25th feb)

November 2002
Hollows appear near the surface of the hill
(Compare to April photo below)

Silbury Picnic.
2nd Anniversary gathering.

You can now watch the documentary
'The Hill with the Hole'
Here
Video

Cementaton skanska return for further scanning.
April 2002

MORE SILBURY HILL SECRETS REVEALED

  Surveys on Silbury Hill, the prehistoric monument near Avebury in Wiltshire, where the partial collapse of an 18th century mining shaft led
  to a hole appearing in 2000 at its summit, have revealed that the hill's structure appears to be stable. But more work must be done before
  this enigmatic chalk mound, built by our Neolithic ancestors 4,500 years ago, finally gives up all its secrets.

  Some fascinating details have already come to light. Archaeologists from English Heritage, the hill's guardian, have for the first time been
  able to make a digital model of the mound, the biggest of its kind in Western Europe. This reveals the possibility that it was built in a spiral
  fashion with a spiral processional way for ceremonial purposes. Chalk cores taken from the mound reveal evidence of the Neolithic
  ‘building site' at its base.

 A 3D seismic survey and other archaeological work were commissioned in the autumn last year by English Heritage to assess the
  condition of the hill and its interior. Several tunnels have been dug into it over the centuries, and English Heritage needed to plot them and
  any other holes before remedial work was contemplated. The collapsed 18th century shaft has already been filled in to protect the
  monument from further damage.

  Dr Kevin Brown, Regional Director of English Heritage, said: "The results of the seismic survey are very encouraging as they have shown
  that the hill's structure appears stable. The survey has revealed, however, that a small part of a tunnel constructed near the base of the hill
  in 1969 has suffered a roof fall. It has confirmed evidence from surface surveys that there is a depression on the north flank of the hill
  which may relate to an area where the chalk has been disturbed.
We are carrying out further tests on this area as soon as possible to discover the exact nature of this anomaly, and a
  section of the central area where the results have been inconclusive."

  The seismic survey was carried out by Cementation Skanska, a leading international engineering company. Small diameter boreholes
  were drilled vertically into the hill and sound waves used to scan its interior for cavities and loose areas of chalk. The results were then
  evaluated by Cementation Skanska, English Heritage and independent experts. A team of experts will shortly be returning to the hill to
  gather more detailed information prior to preparing a full assessment of the hill's future maintenance.

  Research has thrown light on how and when the mound was constructed and its subsequent history. Chalk cores taken from boreholes
  drilled down through the hill for the seismic survey and analysed at English Heritage's Centre for Archaeology at Fort Cumberland,
  Portsmouth, show what conditions were like when the mound was first built.

  English Heritage archaeologist Fachtna McAvoy said: "We can see what is effectively a Neolithic building site at the base of the mound.
  The workmen were evidently struggling with wet ground conditions and churned up the land surface into a mixed layer of chalk and mud.
  We have also discovered that the mound when it was built was 31 metres high and that there were no long layoff periods during its
  construction."

  Members of the public will be able to see the contents of the cores themselves as they have been digitally recorded. The pictures will be
  made available through the Internet after analysis and interpretation has been completed.

  Using geophysical and surface survey techniques archaeologists have discovered that the mound could have been built in a spiral
  fashion, rather than terraced, as had been previously thought. While this may have been to aid construction it could also have provided a
  processional way to the summit. Neolithic art is characterised by its preoccupation with spiral forms. It also appears that the hill is not
  circular but has radial spines linked by straight lines rather like a spider's web. Platforms cut into the sides could date from the period
  when the Romans settled at the base of the mound and may have been used for monuments or altars.

  David Field of English Heritage's Archaeological Field Investigation Unit said: "The digital model of the hill places it within its landscape.
  From this we can see how its lowland setting emphasises its enormous size and also how it has been placed on the very edge of dry
  chalk immediately next to water. We had indications of how important water was to the construction and meaning of the hill when the ditch
  at its base dried out and we could see signs of a substantial linear feature under its surface, extending for 50 metres.
Silbury clearly holds many surprises yet."

  A fragment of an antler pick found during excavations on the summit preparatory to the seismic survey provided the first secure
  radiocarbon dates for the hill itself of about 2490-2340 BC.
 

3D Terrain Models (David Field)

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2001 news
Radio Carbon Dates.                                                  A piece of deer antler has proved that Silbury Hill
                                                  was completed around 4,500  years ago.

                                                  The first scientific evidence for the date of one of the most
                                                  puzzling of our ancient monuments is one of two antlers found at
                                                  the summit of the 130 ft hill.
                                                 The fragments are the broken tips of the picks with which the
                                                  monument was built, that were thrown into the top of the hill as
                                                  the last gaps between the blocks of cut chalk were filled with
                                                  rubble.

                                                  While the first phase of building at Silbury may be centuries
                                                  older, the dating of the antler proves the structure was complete
                                                  almost 1,000 years before the last arrangement of the boulders
                                                  at Stonehenge.

                                                  The dating, by the Oxford University radiocarbon unit, yields a
                                                  late Neolithic date of about 2490-2340BC, with 95% certainty of
                                                  accuracy.

                                                  Although the Roman coins and the scraps of medieval horse
                                                  harness also found in the excavation looked more intriguing, it
                                                  was the antlers which caused most excitement. They were the
                                                  first organic finds from a previously undisturbed part of the
                                                  mound.

---

3D Tomography.
Gloucester based site investigation contractor Geotechnical Engineering sank the 4 boreholes using one of its in-house
developed Pioneer rigs.The 2.7ft rig had to be winched up the steep hillside on a trailor, the same method that was
adopted to take the drilling supplies to the summit.

Dynamic sampling was used to obtain 100% core recovery through the soft, uncompacted chalk down to 30m.
The rig was then switched to rotary drilling to core down through the chalk bedrock.
Cores were boxed up and taken to a coldstore where English Heritage is logging them for archaeological information.
The structure of the hill is being being surveyed using seismic signals released from a source lowered into the
boreholes and picked up with receivers in adjacent boreholes. This will provide geophysical information about
the core of the hill, which is the main area of concern.

A surface seismic survey will also be carried out, with geophones placed in the top of the hill and the sources in the
boreholes as before. This provides geophysical data from the hill core to its surface, allowing a complete model
of the hill to be built up. The software used to interpret and analyse the seismic data from the survey has been developed
by US company NSA Engineering. it converts the raw data into 3D images that can be easily understood.
The colour of the images depends on the seismic velocity of the surveyed rock; cooler colours represent low velocity
seismic waves, ie cavities or low density material, and warmer colours represent higher velocities, strong, dense material.
The 3D model can be picked up and rotated or sliced in any direction and different colours or seismic velocities can be removed
from the model to highlight the lowest or highest velocities.
Investigation work started on the site in August and was completed by the begining of October.

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16th August 2001
Work starts on filling the hole.
A helicopter was used to carry tons of chalk to the top of the hill to stabalise it before 3D scanning starts.

. .

LINKS (Open in new browser window)

Current Archaeology

Head Heritage

BBC On-Line news report

Vandals Admit damaging the inside of  the hill

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