Tunnel collapse: In 2017 and even three months ago, reports had flagged risk and challenges

Indeed, TASPL’s 34-page geological report and 29-page geotechnical report listed in terms of strength and stability the rock types that would have to be cut: “It may be anticipated that the rock type to be encountered along the diversion tunnels would be 20% good (Class II) 50% fair (Class 111) 15% poor (Class IV) and 15% very poor ( Class V) quality.”

The geological report underlined that the alignment was “very unfavourable” in two segments, adding that “the possibility of forming wedges in the crown and side wall cannot be ruled out in those sectors and has to be taken care of during construction planning.” In other words, interlocked individual rock pieces could come apart due to redistribution of pressure due to excavation, making the tunnel’s ceiling and walls vulnerable to collapse.

Another issue is that of escape tunnels. On December 6, in a reply to a question in the Rajya Sabha, Union Highways Minister Nitin Gadkari said that there was a provision of a “separation wall” at the centre of the carriageway along with “egress openings” both for vehicles and pedestrians for “escape” during an emergency.

But this is not what the project plan envisaged. Asked why these dedicated escape tunnels were not in place, a senior project engineer said that a “pragmatic decision” was taken to alter the project plan at the construction stage.

“Instead of leaving an escape channel on the left, it was decided to put the divider in the middle for single-way traffic on either side. This created more space for traffic and eliminated the risk of collision inside the tunnel,” he said on the condition of anonymity.

The geotechnical report also recommended a number of support measures, such as pipe roof umbrellas, pressure grouting, and fully-grouted rock bolts to ensure no adverse events during excavation. The report held that “excavation shall be strictly done as per the excavation sequence/stages/cycles and only after the installation of a support system after each excavation cycle of 750-1000 mm.”

On November 12, when a part of the tunnel collapsed, nearly 90 per cent of the 4.5-km alignment was already excavated from both sides. Asked about the warnings and the accident, a TASPL official said: “These reports are done by consultants we hire on a project basis.”

To ensure that the precautions were followed during excavation was the responsibility of Hyderabad-based contractor Navayuga Engineering and its German advisor Bernard Grouppe, supervised by TPF Getinsa Euroestudios SL of Spain and New Delhi-based Rodic Consultants under the implementing agency NHIDCL.

As recently as last August, barely three months before the tunnel collapsed partially, Bernard Grouppe had also flagged risks. “Since the start of tunnel driving, the geological conditions have proved to be more challenging than predicted in the tender documents, thus confirming the results of the further exploration measures carried out at the beginning of the execution phase,” it said in a note.

Asked if these “challenging” conditions could have contributed to the tunnel collapse, Bernard Grouppe’s India operation manager declined to comment.

The Silkyara-Barkot tunnel is showcased as an “engineering marvel” on the website of Navayuga Engineering. The company has maintained a low profile since it suffered a major setback in Maharashtra where an accident killed 20 workers at one of its highway project sites this August.

Officials at the company’s Hyderabad and Delhi offices said that only the “tunnel project’s field office staff”, who were not immediately available, could comment on the tunnel. Emails to Navayuga’s managing director Chinta Sridhar did not elicit any response.

As the project’s Authority Engineer hired by NHIDCL in 2019, the onus was on TPF Getinsa Euroestudios SL (Spain) and Rodic Consultants Pvt Ltd (New Delhi) to monitor the excavation. Their mandate includes reviewing the contractor’s design and quality assurance plan, approving materials used in the construction, undertaking review of the progress and ensuring timely completion of the project concerned.

Incorporated in Spain in 2012, TPF Getinsa Euroestudios SL belongs to TPF SA of Belgium which has been present in India since 2006 through its Navi Mumbai-based subsidiary S N Bhobe & Associates Private Limited where it holds 51% stake. Incidentally, S N Bhobe & Associates was the Authority Engineer for the Surat flyover which came apart, killing 10 workers, in June 2014. Official reports blamed faulty design for the collapse.

When contacted, Mukesh Gupta, deputy country director of TPF Gentinsa Eurostudios SL, declined to comment.

Rodic Consultants, the NHIDCL’s other supervisory arm, had described the Silkyara tunnel as a “dream project” in the media. Last year, the company was issued a show-cause notice by the MoRTH based on an undisclosed complaint and the matter reached the Lokpal. The case was closed this February after an action taken report from the ministry’s Vigilance section satisfied the anti-corruption authority.

When contacted, Rodic’s CMD Raj Kumar declined to comment.

NHIDCL managing director Mahmood Ahmed did not respond to requests for comments. However, a senior official, who spoke on the condition of anonymity, said: “We expected a more thorough DPR report but the surveys by Bernard (Grouppe) were useful. Tunnelling was a big challenge in such a shear and fracture zone and the alignment developed 21 small and big cavities. But the collapse happened due to the failure of the primary lining in an area that was cut more than four years ago and thought to have stabilised.”

He added that “all necessary precautions” were taken. “Wherever we found cracks and deformities, we went for re-profiling and allowed time before benching or final lining. There was no negligence on our part.”