Real time Tunnel

monitoring system

Owing to their unique design and construction,tunnels call for rigorous SHM programs during bothconstruction and operation phases. Indeed, theircontinuous monitoring can serve to mitigatepotential hazards, ensure better performance andfacilitate in-depth understanding of the overallstructural behavior.

Sacertis has developed an innovative solution forreal time monitoring of traditional and mechanicalexcavated tunnels. It consists of three differentmonitoring approaches:

• Static monitoring to observe the variation in timeof the membrane (hoop) stress distribution in theindividual segments;

• Geometric monitoring to detect the potential

ovalization of the lining;

• Sectional monitoring to check any potential

issues during the construction phase (i.e.

handling, mounting ,TBM thrust effects,..).

Sacertis monitoring sensors consists of clinometerchains, applied on the lining to detect the ongoingdeformed shape, together with patented stresssensors embedded into the concrete to measure itsinternal stress. A GPS referenced gateway, set atthe top of the devices, gathers data and sends themto the cloud through the cellular network, wherethey are stored and cleaned from noise and allinfluences of environmental parameters(temperature, humidity, etc.). The comparisonbetween new and historical data sets allows tomonitor the evolution in time of the appliedactions.

The cloud communication system, coupled with areal-time analysis of the recorded data, emulatesthe behavior of the structure and generates alarmswithin a few seconds of the triggering event. Whenpre-set alarm thresholds are reached, immediatewarnings are issued to everyone concerned. Thecloud environment assures the scalability of theentire system.

The monitored measurements are post-processedinto relevant structural parameters (i.e. hoop forcesand ovalization) and analyzed in a FE model toevaluate the stress state in the lining, as well as thesoil (or water) pressure acting on it.

These structural analyses can assess the severity ofthe defects caused by ordinary (aging) orextraordinary events (earthquake, soil movements,project errors, etc.) in order to mitigate businessinterruption or to plan post event maintenance.

Sacertis devices, tested in top University labs, arenow installed in several tunnels and are supportedby an important ecosystem of global world leadingcompanies (AXA, IBM, STMicroelectronics). The siteongoing monitoring data collected for differenttunnels show a precision of a few thousandth ofone degree. One of the first test, carried outbreaking down the final consolidated diaphragmwall of a highway tunnel, returned highly accurateresults comparable to the georeferencedmeasurements.

To simplify the installation process during the TBMmounting stage, a "Smart Segment" has beenstudied, incorporating stress sensors andinclinometers on the internal surface; a typicalmonitoring set-up (following figure) considers theinstallation of inclinometers in the vault and stresssensors in critical sections of the lining. This sensorsconfiguration can be applied on several transversalsections along the tunnel based on the soilconditions.

Short and long-term tunnel behaviors arereproduced through finite element modeling inorder to represent the structural pre-existing stressstate at the time of installation of the monitoringsystem and its theoretical evolution expected over aN year period from tunnel excavation. The FEmodel is representative of the theoretical tunnelstress state at the beginning and at the end ofmonitoring. Threshold values are set, based on theinformation collected at regular intervals by themonitoring system.

Installiation in existing tunnel - no traffic interruption

The monitoring system

FE Model. North View

SMART SEGMENT- Università di Tor Vergata

Expected deformed shape evolution in time

Example of structural analysis results