Tunnel monitoring

fTB 121 Brillouin distributed fiber optic structural health monitoring system Comprehensive tunnel monitoring Introduction Traditional sensors can only monitor a limited number of preselected locations, potentially leaving crucial spots on structure unmonitored. fibrisTerre’s distributed fTB 2505 fibre optic sensing system is capable of performing truly distributed comprehensive tunnel monitoring that include: • tunnel convergence • crack detection • deformation monitoring • fire detection Further, capable of monitoring upto 25km section of tunnel with up to 5 cm of spatial accuracy, it is a powerful and efficient system that does not leave any part of the tunnel unchecked. Key benefits Truly distributed measurements Capable of measuring as accurate as every 5 m along the sensor cable, the system does not leave any hazardous location unattended More comprehensive data With movements in x, y and z direction monitored, a more realistic understanding of the tunnel structural changes is at your disposal. Precise pin-pointing location With less than one meter resolution unstable slope areas can be narrowed down to a precise location. Economic advantage Automatic monitoring eliminates the need of on-site personnel and the large distance range reduces the per meter cost. Robustness fTB 2505 offers industry leading attenuation budget through which the sensing cables can function even in the harshest environments. Field friendliness Weighing merely 8.5 kg and consuming as little as 50 W of power, fTB 2505 is ideal for the field. About fibrisTerre fibrisTerre is a Berlin, Germany based designer and manufacturer of the pioneering Billouin Frequency Domain Analysis (BOFDA) based fiber-optic sensor. Capable of preforming automatic and truly distributed strain and temperature sensing of all points along its long distance cables, fibrisTerre’s systems leave do not leave any critical spots of a structure unattended. Established in 2009 as a spin-off of the German Federal Institute for Materials Research (BAM), fibrisTerre has been supplying the structural health monitoring industry with its state of the art Brillouin sensing systems. Some of the typical application of fibrisTerre’s systems are: • Early failure detection in geotechnical structures • Fatigue monitoring of bridges, tunnels, dams • Oil and gas pipeline monitoring • Strain and temperature monitoring in mining • Displacement monitoring of river embankments The primary focus of fibrisTerre’s business is to supply its Brillouin read out unit, which offer several key features: • Industry leading data accuracy: < 2 µ for strain and < 0.1°C for temperature • Spatial resolution of 0.5 m over 25 km distance • Superior attenuation budget • Full loop measurement, no return fiber needed • High-precision measurement of fiber length • Access to all raw data • Field friendliness due to light weight and low power consumption When requested fibrisTerre also provides all additional services that are involved in installing and utilizing a Brillouin system: • Tailored service packages for new constructions • Specific solutions for retro-fitting of existing structures • Quality installation and management through • a strong network of partners, cable suppliers and integrators • Long term and reliable maintenance and system upgrade services Convergence monitoring How does it work By integrating fiber optic cables along the cross sections of the tunnel lining, the continuous progress of convergence can be monitored continuously using the fTB 2505. Further, with the 25 km range, a large number of sections of linings can be monitored using just one system, helping you obtain a more complete and up to date picture of convergence throughout the whole tunnel. Installation Ready-to-use cable products are available to glue strain and temperature optical fibers on to tunnel linings. In the case of convergence monitoring cables with pre-strained fiber embedded inside can be used. An alternative method of pre-straining is to use normal cables and strain them manually as they are installed. Expected data Because the installed cables contain pre-strained fibers on the inside, when convergence occurs, the result data would show the strain values at the converged section decrease in comparison to the initial values. Deformation monitoring However does it work Depending on how the tunnel is constructed, the deformation of the tunnels can be detected by monitoring the longitudinal deformation of the tunnel lining and the deformation of soil foundation. There are three possibilities of monitoring - Using 3D cables installed longitudinally along the tunnel lining, - Using Geotextile mats that are place underneath of the tunnel base. - Using pre-strain cabled integrated into vertical boreholes underneath the tunnels. Installation • Longitudinal deformation In order to monitor the longitudinal deformation of the tunnel lining, special 3D cables with 3 fibers embedded inside are available through fibrisTerre to provide tunnel movement profile in x, y and z directions. The installation of such cables is similar to convergence and crack detection cables, which involves adhering these cables onto tunnel linings. • Tunnel base deformation When the foundation soil needs to be monitored for settlement or swelling, geotextile mats or specialized cables can be integrated into the soil. The mats would provide reliable transfer of soil movement to actual strain readings. The geotextile mats are typically placed just below the base of the tunnel. • Foundation soil deformation Settlement and swelling information can be obtained at greater depth when fiber optic cables are integrated into boreholes beneath the tunnel. After drilling vertical boreholes that surpass the sensitive soils layers, pre-strained fiber optic cables can be grouted into the boreholes. Any settlement and swelling of the soil underneath of the tunnel can be timely detected. Crack detection Newly developed cracks can be detected and located by sensing cables. By looking at the data obtained from convergence monitoring cables, a localized increase of strain would indicate the formation of new cracks. Similarly, by looking at the data obtained from deformation monitoring cables installed longitudinally along the tunnel, a localized increase of strain in the x direction would also indicate the formation of new cracks. Fire detection The fTB 2505 system is also capable to simultaneously retrieve temperature data from the fiber optic cables. This capability means that all monitoring cables installed can also be used as fire detectors. Through frequent and continuous monitoring of temperature data throughout the entire length of the cables, overheated location Contact us fibrisTerre GmbH Köpenicker Str. 154 10997 Berlin Germany tel +49 30 6290 1320 info@fibristerre.de www.fibristerre.de