Blackfriars station ground movement monitoring.

James Fisher Strainstall provides an extensive monitoring system for the Blackfriars Station Redevelopment Project in London for Jacobs Engineering UK.

The scheme is part of the Thameslink project to double passenger capacity on the Bedford to Brighton line. The underground part of the station was demolished and excavation of the site underway in April 2010 before construction of a brand new station for both the underground and the main line railway station began. The demolition of the surrounding structures caused the ground to move, initially heaving and eventually settling down again when new buildings were constructed. Such ground movement could cause damage to nearby listed buildings and affect the underground tunnels and railway tracks by reducing the gap (clearance) between the trains and the tunnel linings - an unsafe condition.

The mainline railway and nearby underground lines remained operational during the project. To ensure they operated safely, 10 main areas were monitored including neighbouring listed buildings, services' tunnels containing power, telecoms and gas services, the station area itself, the London Underground District and Circle subsurface tunnels and Waterloo and City deep tunnels. The main components of the system included 13 half arc second Leica automated total stations, around 800 prisms, vibration monitoring systems, Geokon electro-level beams, displacement & crack monitoring, strain gauges and gas leak detection. The vibration systems monitored at 1000 readings/sec, with summary data presented routinely and any events exceeding pre-set limits being recorded as separate event files.

The monitoring systems supplied by James Fisher Strainstall constantly checked for any such changes and alerted the project management team to any potential problems so that remedial action could be taken. 'Real-time' data was presented on a bespoke display for the client. Data was collected from the local systems either by wired landlines, GSM or 3G wireless modems. For Waterloo & City deep tunnels, due to space limitations the instruments deep in the tunnel were controlled remotely at over 1km away.

The data was processed in a central database and then received by the client over the internet, with alarm emails and texts where required on key assets. Manual levelling and surveying data was also added onto the system, with backup audit surveys to compliment the data where required.