Issue link: https://geospatial.trimble.com/en/resources/i/1480709
9/4/2020 CES May 2020 ces.pagelizard.co.uk/webviewer/#cesmay2020/remote_monitoring_of_a_tunnel_under_restoration_and_construction_activity 2/3 Lack of understanding of how tunnels move naturally, particularly those built over 150 years ago and a limited understanding of what external factors could cause it to move further. How to measure a tunnel to an appropriate level of accuracy to satisfy risk models. How to transmit this data out of the tunnel to have a constant insight into its behaviour. How to classify thresholds for movement and what escalation procedures would be needed. How to carry out the process remotely with no need for people inside the tunnel. How to overcome dusty, noisy conditions with low visibility and heavy plant usage, no natural light and no phone signal. There was also the additional problem of the existence of a third-party construction site with active piling and excavation directly above the eastern bore. These challenges created a 'perfect storm' of monitoring conditions with constraints that would limit the number of systems capable of recording movement data in absolute form, at regular intervals, day and night, with no requirement for people to visit the site maximising safety. System considerations Following a 3D finite element analysis (FEA) conducted by Amey Consulting, it was decided that trigger levels should be set for movements of the tunnel in accordance with its results; green (less than 4mm), amber (between 4mm and 7mm) and red (above 7mm). Two systems were presented by Amey Consulting to Network Rail, one based on tilt sensors and one on a total station approach. The total station approach proved to be the most workable and working with KOREC a final system was selected and installed. Installation Upping the original proposal for four high-accuracy total stations to five would provide the best option with communications looked after by five Trimble Settop M1s in toughened cabinets. M1s are robust communication hubs that combine the functionality of a field computer, device server, router and remote switch, streamlining the number of components needed for this monitoring task. However, because there was no phone signal in the tunnel, an alternative method for connection needed to be designed and specified. An OctoHub was used to connect the M1 to a modem via fibre optic cable rather than the usual internal M1 SIM card. This provided fast, robust, efficient data transfer to a 4G gateway at the south portal and in turn to the internet and Trimble's T4D office monitoring software. Inside the tunnel, the five Trimble S5 Ti-M monitoring total stations were positioned and installed by KOREC along with 150 toughened glass prisms placed in arrays throughout the tunnel alongside a network of reference prisms to coordinate all movement to data control points. Collected monitoring data is processed automatically in T4D software, which Amey Consulting is also using to display the results, to output operational and management reports and to manage alerts, alarms, web access and email notifications. This has enabled multiple stakeholders to gain access to historic and live data in real time, understand trends and, most importantly, see the effect of construction activity on the tunnel. Data is also extracted into Amey Consulting's own geotechnical software. Monitoring