Months after Uttarakhand tunnel collapse, panel flags shortcomings in planning

A panel constituted to probe Uttarakhand’s Silkyara tunnel collapse in November has flagged shortcomings in the planning for the project, saying its design report lacked detailed geotechnical and geophysical investigations. It has called for a detailed safety audit of the tunnel while underlining safety should never be compromised to meet the completion targets.

“Prioritizing safety measures is paramount in tunnel construction projects,” the panel said in its 70-page report, a copy of which HT has seen.

Forty-one workers were trapped for 17 days in desperate conditions after a part of the 4.5km-long tunnel collapsed in November. They were pulled from behind a 60m thick wall of debris under the tunnel following a process of manual drilling with the help of the primitive rat-hole mining method. The Uttarakhand government earlier constituted the Shantanu Sarkar-led six-member expert committee to probe the collapse.

Sarkar, the director of Uttarakhand Landslide Mitigation and Management Centre, said they found gaps in the tunnel project. “There was no escape route and an alarm system in case of tragedy. Even monitoring was not proper.”

National Highways Infrastructure Development Corporation (NHIDCL), the tunnel’s executing agency, rejected the report. “We do not agree with the findings. We will not take into cognisance,” said NHIDCL director Anshu Manish Khalkho.

He added they will rely on the report of the Union road transport and highways ministry. “It has submitted a preliminary report...It is not right to say anything for now.”

NHIDCL project manager Deepak Patil referred to the measures before restarting the excavation and said they sent engineers and experts inside the tunnel through the pipes laid for the rescue of the workers to analyse the situation. “...like how much water is accumulated, electricity, machines stationed in the tunnel, oxygen level at different spots, poisonous gases, and structural stability. We took all measures during the inspection with masks on and oxygen.”

He said the experts found everything stable. “We will also send high-quality cameras to record the visuals of the situation inside. We will take all steps first to secure the area and then carry new pumps and operators for dewatering. We are expecting to complete the safety measures in a week or so to start the dewatering process. Once it is completed, we will treat the cavities and the excavation work will be initiated.”

The Sarkar-led panel report said the number of bore-holes during the Design Project Report stage appear insufficient. “Conducting more exploratory bore-holes and geophysical investigations can identify critical geological features and minimize risks during construction.”

The panel called for prioritising comprehensive site studies for future projects to minimise unforeseen geological surprises. “This includes assessing rock formations, seismic activity, and potential risks to ensure that tunnels are designed to withstand the geological challenges of the region.”

Exploratory bore-holes are essential precursors to tunnel construction. They offer insights into the geological and hydrological conditions of the subsurface to determine the feasibility of tunnel construction.

The report highlighted a critical gap—a lack of real-time instrumental monitoring for deformation and stress measurements. “Manual monitoring, conducted periodically, may not provide timely insights into evolving situations. Shifting towards real-time monitoring can offer proactive responses to dynamic conditions within the tunnel,” the report said. It added the tunnel lacked an evacuation plan in the event of a tragedy.

“Implementing an evacuation plan, such as installing concrete hume pipes, is essential to facilitate quick evacuation in the event of a collapse tragedy. Incorporating an alarm system for evacuation is essential to ensure the safety of works....,” it said.

The report suggested formulation of project-specific Standard Operating Procedures and proper training for workers. It said a technical advisory committee comprising experts should be constituted and visit the tunnel at regular intervals. The report said detailed and scenario-specific emergency plans should be tailored for tunnel collapses.

It recommended an interdepartmental coordination committee at the national, state, and district levels for regular monitoring of such projects in the fragile Himalayas.

The panel asked design engineers to conduct regular inspections to identify deviations and implement corrective measures to deal with geological surprises. It said a system should be established for monitoring the structural health of tunnels post-construction. Regular inspections, maintenance, and timely repairs can prevent minor issues from escalating into significant structural problems, the report said.

The report called adherence to construction standards and the use of high-quality materials imperative. It said robust quality control measures during the construction phase can significantly reduce the risk of structural failures. “Adhering to the prescribed rate of tunnel excavation is vital to maintaining stability and preventing unforeseen ground deformations,” the report said.

The report said tunnels must be designed keeping seismic considerations of the Himalayan region in mind. “The proposed recommendations aim to address the gaps identified in the Silkyara tunnel project, enhance safety measures, and inform future tunnel constructions in challenging geological conditions,” the report said.

HT in November reported how a geological report submitted before the commencement of the tunnel project warned of weak rocks and adequate support structure needed to prop them up.

The report said the major rocks in the area were weak sedimentary such as slate and siltstone and the formation of wedges in the crown and side wall cannot be ruled out. “This has to be taken care of during construction planning,” the geological report said.