Six days before the Kerala government halted work at the Wayanad tunnel project, an internal geological report prepared by the project’s sub-contractor had reportedly warned that the slope above the tunnel’s north portal could fail at any moment under prevailing monsoon conditions.
The landslide struck the north portal of the under-construction tunnel in Wayanad on Tuesday, killing six people and raising serious questions over slope stability and safety measures at the site.
Report highlighted severe slope instability
According to the internal assessment prepared by Dilip Buildcon Limited (DBL), the sub-contractor handling the tunnel work, the hillside above the north portal had already begun showing signs of structural distress.
The report was jointly prepared by DBL senior geologist Raju Sagar, Geological Survey of India (GSI) official A. Ramesh Kumar and Authority Engineer Dr H.K. Singh from Turkish Engineering Consulting & Contracting.
The assessment covered inspections carried out between June 3 and June 11 at the north portal near Kalladi-Meppadi in Wayanad.
Engineers found that the slope consisted of nearly 35 metres of loose silty soil over hard rock. The report noted that this type of soil retains water during heavy rainfall, increasing its weight while reducing stability and making it vulnerable to landslides.
Despite slope protection measures including stepped cutting, shotcrete and soil nailing, engineers observed widening cracks, soil movement, muddy seepage and cavities developing within the slope.
Underground water flow raised major concerns
One of the report’s key findings was the presence of underground water flowing between two support levels inside the slope.
According to the assessment, such internal water movement could erode the soil from within, significantly weakening the hillside and increasing the likelihood of a sudden collapse.
The report specifically identified the left side of the north portal as carrying a much higher risk than the right slope and warned that, under existing rainfall conditions, it “may culminate in sudden slope failure at any time.”
Safety systems found to be inadequate
The report also pointed to shortcomings in the site’s safety infrastructure.
It found that several drainage holes designed to reduce water pressure inside the slope were either ineffective or not functioning properly on the high-risk section. It also noted that piezometers, which monitor underground water pressure and provide early warning of slope instability, had not yet been installed.
The assessment added that the existing monitoring equipment was not accurately reflecting the visible signs of distress observed at the site.
Blasting not identified as primary cause
Trial blasting for tunnel excavation was conducted on June 5, June 6 and June 11 while the slope was already showing signs of instability.
However, the report concluded that recorded blast vibrations remained within permissible limits and indicated that prolonged heavy rainfall, rather than blasting, was the primary factor behind the slope deterioration.
Engineers recommended multiple corrective measures
The internal assessment recommended several immediate measures to improve slope stability.
These included constructing gabion retaining walls along the vulnerable left slope, covering exposed soil with protective matting and tarpaulin, creating lined drainage channels to divert rainwater, and carrying out field tests to verify the effectiveness of existing soil nails and drainage systems under saturated conditions.
The report also expressed concern over the location of a nearby concrete batching plant, stating that its weight and heavy vehicle movement could further affect slope stability. It recommended relocating the facility away from the vulnerable area.
Contractor and project authorities respond
Project authorities said the report had primarily been commissioned to assess the impact of blasting activities.
An engineer associated with Konkan Railway Corporation reportedly said work at the north portal was stopped after the findings emerged.
The engineer maintained that shotcrete was used alongside 12-metre-long concrete anchor rods installed at two-metre intervals to strengthen the slope. He also claimed that the landslide occurring above the site would have been difficult to prevent through conventional safety measures.
When asked about monsoon preparedness and slope protection, project representatives said standard engineering practices had been followed. However, they did not provide a clear explanation regarding the status of gabion wall construction or whether there had been shortcomings in preparing the site for tunnel work.
The contractor also stated that delays in government land allocation for storing excavated soil affected project logistics.
Following the landslide, the engineer said nearly 200 workers at the project’s south portal left the site out of fear and that construction would not resume until an expert committee appointed by the Kerala government approved future safety measures.
The internal report was prepared days before the District Collector issued a stop-work order on June 20, indicating that work at the north portal had already been halted amid growing concerns over slope stability.