Agencies blamed for negligence for Silkyara tunnel collapse

NEW DELHI: The final probe report on last year’s Silkyara tunnel collapse in Uttarakhand has found negligence on part of the entity that prepared the detailed project report (DPR), construction firm, supervision consultant or authority engineer (AE), and National Highway and Infrastructure Development Corporation (NHIDCL).
It said the fixing of alignment did not meet basic principles of tunnelling, and there was negligence on part of the contractor to address the issue of 21 minor collapses, despite AE flagging them.
Sources said the probe panel headed by former Border Road Organisation director general R K Dhiman submitted the report to the road transport ministry last week.
Highlighting the lack of coordination and information flow among the stakeholders and how they overlooked responsibilities, the panel has recommended that the govt may initiate penal action against delinquent personnel and officers after carrying out an inquiry.
“We will study and take necessary action,” a top ministry official said.
TOI has learnt that probe found that the DPR was based on limited geological and geotechnical investigations, the alignment could have been modified to eliminate weak or shear zones, and no expert third party review was done, which was a deviation from normal practice.
The report highlighted how the construction company did not conduct a proper investigation, and there were issues with design and execution.
It has flagged incompetence of contractor, AE and approving authority NHIDCL, mentioning that evidence showed no measure was taken to address the shear zone issue.
Shear zone refers to highly deformed, weak and thinned rocks due to high level of regional stress, and such zones require special attention, greater monitoring of ground behaviour and more support to avoid any mishap.
As per the report, incorrect value of rock mass rating (RMR) was adopted to keep the rock mass classification as Class-IV instead of Class-V, which was the primary reason for several minor collapses.
It said an adequate monitoring plan was not implemented due to which correct deformation details were not established. The deformations were not being addressed properly, which was one of the reasons for the massive collapse that resulted in 41 workers getting trapped for 17 days.
The report has mentioned how reprofiling was carried out in distressed zones without ensuring the safety and safe passage of workers, and how the methodology for reprofiling was not vetted by AE. Senior geologist and material engineer, who play a key role in identifying geology and ensuring quality of work, were also absent during the last one year.
For completion of the project, the panel has recommended clearing off debris in the collapsed section and conducting a detailed inspection of inaccessible sections of the tunnel for condition assessment. It has suggested immediate dewatering, and redesign and modification of the construction methodology to align geological conditions.