Precise remote monitoring predicts movement and stress as Gothic vaulting is cut open. Ramboll
Such major intervention in a cathedral of this age is a world first because it involves cutting an opening in the centre of a medieval floor and quadripartite stone masonry vault. The opening is for a lift that will carry visitors to the upper level of a new exhibition centre in the Cathedral’s South Transept. This will improve visitor access to the Cathedral’s greatest treasures, including the world-famous Winchester Bible, which are currently seen by only 10% of visitors. The £20.5m project is partially funded by the Heritage Lottery Fund.
Developing the opening in the vault has the potential to introduce structural instability, albeit locally and there is the possibility of damage caused in the past by ground movement. Ramboll was approached by Dyer & Butler in 2016 to provide services in surveying, analysis, modelling, monitoring and lift setting out.
The first step to deal with the geometric complexity was to use visible lasers to set out the works before they were surveyed by the Ramboll Geomatics team using a terrestrial 3D laser scanner. The resulting precise measurements and point cloud were then used to build a 3D geometry model of the existing environment, proposed lift and alterations.
Then, Ramboll’s Engineering Simulation team used the 3D model to build numerical models based on solid Finite Element analysis. Movement and stress predictions by Ramboll are now being used to optimise the construction sequencing and to simulate the response of the vault to the alterations. A monitoring regime has been designed with movement trigger levels agreed in advance, each requiring different responses.
For the first time the Geomatics team are using a wireless monitoring system, which uses sensors fixed to the existing structure and which remotely send readings to a central hub (gateway). The gateway uses a mobile phone modem to upload data to cloud storage from which the design team are able to access measurements. Four tilt sensors are being used on this project, but there are no limits to the amount of sensors (tilt, strain and distance measurement) which can be linked into one system.
Winchester Cathedral is one of the largest Cathedrals in Europe with the longest Nave and greatest overall length of any Gothic Cathedral in Europe. It was founded in 1079 and extensively remodelled over five centuries.
This monitoring process has also been used by Ramboll’s Geomatics team on a railway bridge in Manchester, to monitor any movement of the bridge abutments during the crossing of a train, with sensors for measuring distance and tilt at a frequency of 1 reading per second.