The dangers that may arise in the metro tunnels stopped after the 5.8 magnitude earthquake that put Istanbul residents on the streets came to the fore again. The statement made by the TMMOB Chamber of Mining Engineers included the potential dangers and things to do with the subway tunnels that were excavated.

Drawing attention to the fact that underground works are carried out in the city and under the areas where construction is intense, the Chamber of Mining Engineers said, “In the areas where the shaft and tunnels (vertical, horizontal and inclined underground openings) have been opened but whose final fortifications have not been built, tunnel and environmental safety For the below mentioned measures and the necessary measures should be taken immediately ”.

The said statement of the TMMOB Chamber of Mining Engineers is as follows: After the earthquakes that took place in Istanbul on 24 and 26 September 2019, issues regarding the earthquake in public and the dangers that may arise in metro tunnels stopped. As the Chamber of Mining Engineers, we warned the IMM management of the period with the press release regarding the dangers that may be experienced on January 5, 2018 after the stop of the metro tunnels, and stated that measures should be taken against possible dangers in terms of life safety of the people. Although there were no earthquakes 11 months after our announcement, while the excavations were going on, a dent occurred on the Bostancı-Dudullu Metro Line, 2 workers lost their lives in this business murder, and we warned the IMM and the public about the issue.

When designing the tunnels, the seismicity of the investigated areas should also be taken into consideration. Following the implementation of the projects, the tunnel and surface movements should be monitored. In any anomaly seen and measured, the control and support or strengthening of the area should be done urgently. In order to prevent deformations that may occur during tunnel excavations and construction activities, related geotechnical measurements and follow-ups should be taken and necessary measures should be taken and strengthening activities should be performed.

Our disclosure of the dangers and actions to be taken in relation to discontinued metro projects continues to be valid today as it becomes even more important with earthquakes and possible earthquakes. Once again, we share with the public the potential dangers and actions to be taken regarding the underground tunnels that have been excavated:

The underground works are carried out in the city and under the densely populated areas. The most important factor in urban tunneling is that the surface structures are not affected by underground excavations and construction works. Therefore, serious monitoring and measurements are made on the surface and surface effect maps are produced.

In underground works;

1-An opening in the underground is to disrupt the static balance on the surface, that is, the balance of nature.
2-Nature will try to restore this disturbed balance.
3-In order to create a force against this behavior of nature, temporary support (artificial reinforcement) is performed in the tunnel. This first fortification in tunnels is temporary fortification.
4-Temporary support has the time to carry the incoming load. Before this period, the final support (Reinforced or unreinforced Concrete Coating) is made. After the final fortification, the tunnel is secured to the carrier.
5-With this support, the stresses and loads on the tunnel are distributed homogeneously and the tunnel remains within acceptable deformations.
6-If this support / support cannot be performed, firstly an increase in the deformations of the tunnel is observed and then the deformations begin on the surface.

Due to the reasons mentioned above; In the areas where shafts and tunnels (vertical, horizontal and inclined underground openings) of which the construction of discontinued projects have been started but the final fortification has not been made, the following measures and necessary precautions should be taken immediately for the tunnel and environmental safety.

1-As it is not yet known how long the projects will stop, the concrete of the tunnels / areas opened by underground excavations should be completed.
2-In the tunnels provided with shaft (vertical shaft), shaft tops should be covered.
3-If the tunnel concrete pavement, ie the final fortifications are not made and the tunnels are left as they are, the necessary precautions cannot be taken in the tunnel since the vertical and lateral movements within the tunnel cannot be measured during the waiting period, this will cause both the deformations in the tunnel and the surface structures to be affected.
4-Deformations on the surface can cause structural damage to structures / buildings. For this reason, deformations in the tunnels during the waiting period should be monitored regularly using appropriate methods.
5-The deformations in the tunnels cause additional fortifications during the resumption of the work, leading to increased costs.
6-In the tunnels with water income, water supply must be stopped. Taking the water into the tunnel can cause deformations on the surface.
7-Failure to control groundwater may cause damage to the water-sewage-energy-transmission-natural gas lines around the tunnel.
8-Environmental safety must be ensured since the construction sites that are stopped and closed are located in their living spaces.