St Mary Abchurch
The Diocese of London, PCC of St Mary Abchurch and the Friends of City Churches
St Mary Abchurch is first mentioned in the late-twelfth century, but the medieval church was damaged beyond repair by the Great Fire in 1666. The present church is by Sir Christopher Wren and dates from 1681-6, although a medieval vaulted chamber still survives beneath Abchurch Yard. The church is now listed grade I and is noted for its grand interior timber framed dome, lined with plaster and highly decorated. The building, particularly the dome was severely bomb damaged in 1940 but carefully restored after the war.
Bank Station nearby is an important hub on the London Underground being the intersecton of the Central and Northern lines and the and the terminus of the Docklands Light Railway. To modernise the poor access from street level and labyrinthine circulation routes, London Underground initiated an complex scheme of above and below ground improvements, Bank Station Capacity Upgrade. The proposals included a new running tunnel about 23m below ground level and directly under St Mary Abchurch. Since, at 1mile length, the tunnel was too short for a tunnel boring machine as is normal practice and instead would be constructed by machine excavation and a sprayed concrete lining.
Ayesa role included a detailed study of the building and the considerable body of documentation assembled by LUL’s advisors and contractors, advice on behalf of the church on the likely effects of the tunnelling, assessment of the proposed mitigation measures to the window openings and the timber framed dome and attendance at weekly meetings during the critical period of the work. Sophisticated real time monitoring systems were installed including a unique application of a specialised fibre optic cable which could detect infinitesimal changes in length, both on the main walls and around the dome to provide a much greater than normal body of knowledge about the behaviour of an 18th C building to below ground disturbance.
Innovation and Value added
Building on their detailed first hand knowledge of more traditional monitoring systems and response to tunnelling gained in earlier projects Ayesa were able to act as informed and compelling advocates and advisors on behalf of the valued historic asset.