A geological report had indicated a high risk ‘fault zone’ five years before the collapse of a section on the SLBC tunnel in Telangana, which left eight workers trapped on February 22, as per a report by The Indian Express. The report commissioned by Jaiprakash Associates Ltd highlighted the weak formation of rocks and water retention risks. It also warned that certain stretches of the tunnel were vulnerable to collapse because of reduction in rock stiffness and possible water seepage.
Report highlighted a fault zone in 2020
The Tunnel Seismic Prediction (TSP) -303 Plus report prepared by Amberg tech AG was submitted in January 2020. The survey pointed out a fault zone between 13,882 metres and 13,914 metres from the tunnel entrance. The report also identified weak rock mass, water bearing zones and possible structural instability.
Jaiprakash Associates Ltd which had been awarded the tunnelling contract in 2005, admitted the existence of the report but declined to elaborate, stating, ‘’We have no comment on this, ‘’ as quoted by The Indian Express. The findings indicated a higher chance of collapse, urging caution in the affected area.
The evaluation was conducted by transmitting seismic waves into the rock mass and assessing the abnormalities. The analysis discovered rock stiffness and potential jointed or sheared rock masses. Despite these warnings, it is still now clear whether this crucial information was shared with the Telangana Irrigation Department. A senior official related to the SLBC project mentioned that he does not remember reviewing this report.
The collapse took place near the identified fault zone, where the tunnel’s roof caved in approximately three metres around this area. Rescue operations have faced major obstruction because of continuous flooding inside the tunnel.
In response to the incident, experts from various agencies like the National Disaster Response Force (NDRF), State Disaster Response Force (SDRF) have been deployed. Advanced technologies like robotics and seismic studies are being explored to track and reach the trapped workers. To conduct the search operations, cadaver dogs from the Kerala Police and an NDRF sniffer dog have also been brought in.
Lack of geological assessment of the project
According to The Indian Express report, the SLBC tunnel project has faced investigation because of its initial geological assessments. A 2020 research paper co-authored by former Director General of the Geological Survey of India, Jaiprakash Associates geologist, Ritu Deshmukh and Mandapalli Raju stated that the tunnel construction work started without subsurface exploration. Due to the restrictions within the Tiger Reserve Forest,detailed investigations like excavating drifts, and drilling boreholes along the tunnel alignment were not allowed, leading to construction based on limited preliminary evaluations.
The rescue operations to save eight workers trapped inside the SLBC tunnel entered its 13 days on Thursday. The teams are continuing their efforts to reach out to the stranded since the tunnel collapsed.