Dehradun, February 21: A government-appointed panel investigating the collapse of the Silkyara tunnel, which left 41 workers trapped for 17 days, has uncovered critical deficiencies in the project's planning phase. The detailed project report (DPR) failed to include crucial "geotechnical and geophysical" investigations, according to the findings disclosed by the panel. Furthermore, the report highlighted the absence of adequate evacuation plans in case of a collapse, shedding light on fundamental shortcomings in the project's inception.
The 70-page report, submitted to the government in December, scrutinized "critical" geological and construction aspects overlooked during the construction of the strategic tunnel, which aimed to reduce travel time between Silkyara and Barkot by an hour.
"Future projects must prioritize comprehensive site studies to minimize unforeseen geological surprises. Conducting thorough geological surveys before initiating tunnel projects is critical to ensure their resilience against regional geological challenges," the report emphasized.
Insufficient Exploration Of Mountain
Established on November 12 by the Uttarakhand government, the six-member expert committee, led by Shantanu Sarkar, director of Uttarakhand Landslide Mitigation and Management Centre, underscored insufficient exploration of the mountain during the DPR preparation stage.
"The number of boreholes during the DPR stage appears insufficient. More exploratory boreholes and geophysical investigations can identify critical geological features and minimize risks during construction," the report added.
Exploratory boreholes serve as essential precursors for tunnel construction, offering insights into subsurface geological and hydrological conditions to determine feasibility. However, the report refrained from specifying the number and locations of the boreholes.
'Overburden' Site
Highlighting the considerable "overburden" at the site due to oak, pine, and deodar trees, the report outlined the hill's unstable rock structure, comprising slate, siltstone, dolomite, phyllite, and quartzite. It noted that at the collapse site, rocks were predominantly thin to moderately foliated siltstone.
"Subsidence is occurring at the shear zone, indicating vulnerability at specific geological formations," the report noted, recording "deformation suffered by the rock" at the collapse site, suggesting inadequate investigation in the DPR.
Moreover, the committee lamented the absence of a clear evacuation plan in the event of a tragedy, proposing the installation of concrete pipes and an alarm system as essential measures. Emphasizing the paramount importance of safety, the report called for a detailed "safety audit" of the Silkyara-Barkot tunnel, asserting that deadlines should not compromise safety standards.
To prevent similar incidents, the report recommended project-specific standard operating procedures (SOPs), comprehensive worker training, and the establishment of a technical advisory committee comprising experts from agencies such as GSI, NGRI, Wadia, ONGC, and RVNL. It advocated for detailed scenario-specific emergency plans for tunnel collapse scenarios and designing tunnels with seismic considerations of the Himalayan region.
"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 concluded.
