Monitoring tunnels for vibrations and deformations is not only critical during the construction phase but also their service life.
In 2012, the Tokyo-bound Sasago Tunnel suffered significant damage when nearly 150 concrete ceiling panels collapsed and crushed three vehicles, including a van carrying six people that caught fire. The deficiencies in mounting components of the ceiling panels were to blame.
But, are tunnels safe during an earthquake?
A common belief that underground structures are safer because they move with the soil, while structures above ground sway back and forth during the earthquakes appears to be misleading. The impact of earthquakes on tunnels can be severe due to ground failures such as liquefaction, strong ground shaking, and fault crossing.
Liquefaction takes place when saturated soft soil deposits loose load-carrying capacity during strong shaking. This phenomenon can cause the ground surrounding tunnels to deform and shift, with potentially severe impacts. The slope instability and fault crossings may also create permanent deformations leading to a collapse of the tunnel.
After the 1906 San Francisco earthquake, the Wrights railway tunnel in southern Santa Cruz mountains was closed for more than a year due to the collapse of approximately 100-m-long part crossing the San Andreas Fault Zone. Another railway tunnel crossing the White Wolf Fault was seriously damaged during the 1952 magnitude 7.5 Kern County earthquake associated with this fault (Kontogianni and Stiros, 2003).
In 1999 a magnitude 7.2 hit the Duzce region in Turkey. Close to the fault rupture, twin highway tunnels on the major highway connecting Ankara to Istanbul were under construction. The tunnels were partially collapsed due to intense pulses of earthquake motion (near-fault effects) as their lines cross the shear zone of the North Anatolian Fault.
The excavation process during tunnel construction may itself trigger microearthquakes. The vibrations, therefore need to be monitored to identify such seismic activity whether they create any movements or cracks on the tunnel surface. The monitoring vibrations is also needed to estimate the rock formations ahead of the tunnel face to optimize the excavation parameters. Besides, the infrastructure surrounding the tunnel including buildings must be monitored especially in case of construction of new subway (metro) lines.
Structural health monitoring (SHM) system is essential for the seismic resilience of tunnels. A robust real-time SHM system not only allows for assessment of accelerations and deformations (displacements and strains) in tunnel linings but also facilitates the implementation of adaptive risk management. Such a system can assist the officials to make informed and timely decisions to protect people (such as drivers or construction workers) from life-threatening conditions. For example, the highway tunnel can be closed to traffic before any severe consequences take place. Such pro-active actions would not only save lives but also avoid liabilities.
QuakeLogic is the only company providing cloud-based AI-powered disaster risk management solutions to prevent and reduce human and economic losses risen during and after earthquakes. Our cutting-edge technology platform performs real-time autonomous structural assessments using sensor data and sends rapid notifications after an event with the level of shaking intensity and whether structural integrity is compromised. For tunnels, our platform provides meaningful and easy-to-understand information immediately after an earthquake. This timely and critical information helps the officials to plan their emergency response. We also provide a web-based display where the sensor information can be monitored in real-time. This solution can provide great benefits especially for tunnels under construction phase.
For emergency measures and safety of tunnels, QuakeLogic provides advanced monitoring systems together with real-time and autonomous data analytics.