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.