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Studying the evidence

Monitoring during construction of London's Jubilee Line Extension created important case studies for urban tunnelling. Fin Jardine explains how the data will be disseminated

A unique range of buildings, some irreplaceable, some historic, some prestigious, were affected by construction of the London Underground Jubilee Line Extension. These include landmarks like the Ritz Hotel, the Royal Automobile Club, The Treasury, the Institution of Civil Engineers and, most important of all, the clocktower of the Palace of Westminster, which houses Big Ben.

Most of the buildings along the route are more mundane, but many are substantial structures, such as the seven and 10 storey Elizabeth House near Waterloo Station and the towerblocks of Columbia and Regina Points in Bermondsey.

Around the complex Southwark station excavations there are sharp contrasts between post-war office blocks and old masonry buildings, still conforming to medieval boundaries. Further east into Bermondsey, the tunnelling route went below two and three storey blocks of flats where response to the tunnelling works was not certain.

Protection of buildings was only one of the enormous challenges the JLE presented to its promoter, designers and contractors. That this challenge was overcome is enormously important for future tunnelling in London and other metropolises.

Before the JLE works started, one of the real difficulties faced was the distinct lack of well-documented case histories.

This was true even for buildings known to have been seriously affected by construction of the initial Jubilee and Victoria lines.

JLE therefore presented a great opportunity, particularly given the pioneering use of compensation grouting as a safeguard against movement of the at risk structures. As one of construction research body CIRIA's advisory committees commented at the outset: 'The viability of future urban tunnelling, particularly in London, will largely depend upon compensation grouting being successful'.

This evidence has been gathered. It is equally important that the researchquality measurements and observations gained at such great cost to the construction works are not lost. Engineers, asset owners and their insurers of future infrastructure works will want to see and study the case history data to confirm need and reliability, and to look for money and time savings.

To make that evidence available, a book of 30 case histories of buildings along the JLE route is being compiled.

Information is fed in from results of a CIRIA-led LINK CMR research project, Subsidence damage to buildings: prediction, protection and repair , sponsored by the Engineering & Physical Sciences Research Council, the Department of the Environment, Transport and the Regions and the construction industry.

The case histories will form part of discussions at the second string to CIRIA's work - a conference entitled 'The response of buildings to excavationinduced ground movements' be held at Imperial College, London on 17 and 18 July 2001.

Since completion of the JLE, practice and research have moved on, and it will be timely to showcase these developments. The principal themes will be:

Prediction of damage to buildings, including subsurface structures, utilities and other facilities The effect of building stiffness The effect of different configurations of tunnels Effectiveness and viability of protective measures, particularly compensation grouting and other new techniques Management of the monitoring process Long term effects A keynote address will be given by Professor Robert Mair of Cambridge University and the closing address will be by Professor John Burland of Imperial College.

The conference will also feature new UK and international research and developments in the methods of monitoring, damage prediction and protection.

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