Before the demolition process began, manual monitoring regimes were established within the District Line and Piccadilly line tunnels to monitor the tunnel structures and the tracks, as well as the other structures previously mentioned. As demolition progressed, the Earls Court 2 deck and adjacent Network Rail tracks were also monitored. With more than 3,000 monitoring points across the project, the process of manually checking all the assets takes around six weeks.

PC Monitoring was also appointed to install, commission and maintain an Automated Total Station (ATS) system within one of the Down Ealing District Line running tunnels. Being of Victorian brick arch construction, these tunnels are particularly sensitive and any sign of heave (lifting of the tunnels as the heavy portal beams above were removed) had to be closely monitored over a sustained period of time.

The ATS system consists of four Topcon MS1AX Total Stations that are mounted on a bracket at a height of 3-4m. Each one is housed in its own box and the four are placed some 70m apart. The automated monitoring data is presented to the client using cloud-based Mission OS visualisation software which enables instant access to data that is refreshed on an hourly basis.

In collaboration with the consultant engineer, Arup, trigger levels were set for all monitoring systems to ensure that the necessary stakeholders are instantly informed if agreed movement thresholds are crossed at any time.

In addition to the automated system, a dedicated monitoring team was on-call to monitor the other District Line tunnels before, during and after the beam lift/ removal. The tunnel-covering slabs were monitored using precise levelling techniques to understand if the tunnels’ roof slab and abutments had heaved during the beam removal process. Data was quickly processed and immediately reported to LU, Arup, Keltbray and Capco.