New Delhi: The primary investigation report about the recent tunnel collapse in Uttarkashi’s Silkyara several factors that led to the incident, TOI reported.

The factors include the misalignment of the project along the 'shear zone' and the contractor performing 're-profiling' work without implementing sufficient precautions, despite being aware of the vulnerabilities in the area based on past instances of cavities leading to collapses.

The report also highlights that the contractor failed to obtain approval for the work methodology from the authority engineer appointed by NHIDCL.

On 12 November 2023, a section of the Silkyara Bend–Barkot tunnel, planned to connect National Highway 134 in the Uttarkashi district of Uttarakhand, caved in while under construction. The collapse occurred at around 05:30 am and trapped 41 workers inside the tunnel

The labourers were trapped in a 400-metre buffer zone of the unfinished main tunnel of the 4.5-km tunnel on the Brahmakhal-Yamunotri National Highway.

The tunnel - meant to join Silkyara and Dandalgaon in Uttarkashi - is a part of the Char Dham project.

According to a TOI report, the experts' panel submitted a report to the road transport ministry on Friday, underscoring the insufficient deployment of sensors and instruments during re-profiling work.

This prevented the capture of ground behaviour data, which could have informed necessary precautions.

The incident also brings attention to the inadequate supervision by officials of the National Highway and Infrastructure Development Corporation (NHIDCL), a company under the road transport ministry, as well as its authority engineer, TOI reported, citing the panel's findings.

A "shear zone" denotes rocks that are highly deformed, weakened, and thinned due to regional stress.

Such zones demand special attention, heightened monitoring of ground behaviour, and additional support to prevent mishaps.

Re-profiling is a process conducted in tunnel projects to address abnormalities like cavities and deformation before the final lining is implemented.

In this instance, re-profiling became necessary because a proper support system was not initially provided immediately after the excavation.

According to sources, the report pointed out instances of cavities on two previous occasions, signalling that the contractor should have exercised greater caution during their work, the TOI report said.

It is also highlighted that NHIDCL should have enforced rigorous supervision and monitoring of the project, especially given that one of its senior officials acknowledged the occurrence of 21 small collapses (cavities) before the significant incident that left 41 workers trapped for 17 days.

The report has made recommendations for avoiding similar incidents in the future. It proposes the setting up of a tunnel center for road and railways, the creating of a new standard operating procedure (SOP) for tunnel safety, and the forming of a "geological collaborative framework" on the Gati Shakti platform, accord ing to the news report.

These measures will enhance the planning and execution of projects, fit for the Himalayan region.

The panel, consisting of officials from the Border Roads Organisation, railways, and two professors, is set to submit its final report following a comprehensive review of the detailed project report, design reports submitted by the project contractor, and geological mapping.