In November 29th, a tunnel entrance collapsed and the spectacular failure was caught on camera.
According to an article in the newspaper Hurriyet, the tunnel is located in Yusufeli district of Erzurum, Turkey. The failure is connected to the Yusufeli dam located in close proximity with the construction site. The site was evacuated on Tuesday (29th November) and the collapse occured at 9:00am on Wednesday. No fatalities were encountered due to the immediate actions of both the Designer and Contractor’s safety engineers.
Ruler dealt with the safety and risk engineering considerations of tunnel portals in a relatively recent blog, following a landslide failure triggered by heavy rain in a hydro project under construction in Fujian’s Taining County in China.
The same questions arise here, i.e. was it foreseeable or unforeseen? Was there a proper risk assessment carried out and could the failure and its consequences have been avoided?
Quoting from our previous blog, particular attention must be paid to the portal areas of the tunnels in Hydro projects, including headrace, pressure and construction adits, and to the location of the dams and the powerhouses. It is imperative that a landslide hazard map is prepared in the design and construction stages, indicating the hazard impact and likelihood, making use of the all the available information, i.e. from geological maps and aerial photographs to geophysical campaigns and intrusive ground investigations. Detailed ground investigations may be necessary for assessment of small areas and specific sites during construction. Based on a study as such, an assessment of the risk can be performed and particular landslide risk mitigation measures may or may not be deemed necessary. The hazards can range from catastrophic and dramatic effects to the barely perceptible but persistent processes such as slow creep movements and localised rockfall events. The areas that will be assessed as major or critical risk must be avoided during optimisation of the different scheme layouts. Those rated as moderate risk must mostly be avoided. Where areas rated as moderate risk will be unavoidable, mitigation or monitoring measures shall be designed and put in place as part of the detailed design. Landslide hazards resulting from seismic activity must be identified as well since the seismicity will act as a trigger increasing the likelihood of landslide events.
In this case of the tunnel entrance collapse, did a landslide hazard assessment take place prior to locating the portal? Was there an active instrumentation and monitoring campaign carried out? Answering these questions post failure is the result of a forensic investigation, in most cases accompanied with severe and adverse impact on the construction schedule and project budget. Is it worth ‘investing’ in early risk engineering involvement and hazard identification and mitigation? A rhetoric question!
