For the Val di Sambro tunnel, an “OF TUNNEL” system has been studied, designed and installed to monitor the convergence and longitudinal deformations of the tunnel, since it is located in ground subject to landslides.
Location: Apennine stretch between Sasso Marconi and Barberino del Mugello
Client: Spea Engineering – Atlantia Group
Duration of the monitoring service: 38 months
Project start date: 2017
The “OF” System monitors longitudinal deformations caused by thrusts due to the surrounding terrain and measures convergence at key points in the tunnel.
Three lines of sensors are installed throughout the tunnel. In addition, thermal sensors are installed at a predefined distance to compensate for seasonal temperature variations affecting the strain sensors and thus obtain pure mechanical strain values. In this way it is possible to monitor the longitudinal movements of the tunnel, i.e. whether the tunnel “maintains” its design shape.
For further monitoring, about 20 sensors were installed at the two critical points of the tunnel to check the convergence, i.e. to verify that the tunnel maintains its radius of curvature.
In the event of anomalies, if a sensor detects a deformation greater than a predefined value, the system sends an alarm by email to warn that that particular sensor, at that particular point, is registering a tension above the safety threshold. This makes it possible to intervene promptly and punctually in the area concerned.
The sensors used are strain and thermal sensors and are connected to a single acquirer on which the “OF” software runs for real-time analysis of the quantities to be monitored.
The measurements are carried out at a rate of ten data per second from each sensor simultaneously, more than 780 sensors installed, about 30 km of optical fibre laid, 7800 data per second acquired by the system operating 24 hours a day, 365 days a year.
NTSG supports the customer in the analysis of the data and the maintenance of the system, providing the customer with a web interface for viewing and controlling the readings taken by the system and the alarms recorded.
30 km of optical fibre
7,800 data per second acquired
20 technicians/engineers involved in installation
18 days for system installation