STRUCTURE MONITORING specialist Sol Data's inconspicuous site hut alongside London's Kings Cross station receives over 13,500 readings an hour from a network of a dozen theodolites and 1,000 targets. These are scattered throughout the maze of Victorian station buildings and tunnels, with the majority of the 60mm diameter mirrored prism targets on the facades of both Kings Cross and the nearby St Pancras stations.
Automated theodolites mounted on roofs and in tunnel crowns constantly turn as they seek out their prescribed targets. Any structural movement greater than 1mm will be detected immediately by Sol Data's team.
Set up under a £2.6M contract, Sol Data's network is designed to monitor movement around the congested site during the construction of massive new works to rationalise and improve passenger flows below ground.
New ticket halls, pedestrian concourses, subway tunnels and lift shafts will be needed to meet both the recommendations from the investigation into the 1987 Kings Cross fire and the imminent arrival of the Channel Tunnel Rail Link.
Each £25,000 Cyclops theodolite has its own on-board computers and takes a reading of a target in its network every 12 seconds. Data is fed by radio link to the 100GB bank of seven computers in Sol Data's site hut.
Converting the data into useable three dimensional co-ordinates takes about one hour - although this can be cut to 30 minutes.
Each key section of the site has its own trigger values for structural movement, typically 5mm, and if this is exceeded a computer generated alarm signal is sent to the core survey team, day or night.
Designer for the whole project is Arup; project manager is Hornagold & Hills.