Throughout the ongoing rainy season, various government agencies, including the Met Department, have been issuing warnings about likely catastrophic events. Many advisories were issued regarding various activities such as tourism, pilgrimages, the Kanwar Yatra, etc. The layperson may well ask, ‘Were these not applicable to construction projects, particularly in the hills?” Was it necessary to continue tunneling at the THDC project in Pipalkoti at a time when heavy rainfall was taking place? Does not civil engineering require factoring in such parameters during high-risk activities such as tunneling? Is the pressure to reach deadlines so great that even common sense is not applied while functioning? Should such tasks be undertaken during the monsoons?
It is expected that the inquiry into the tunnel subsidence that has caused, at least, loss of seven lives, will consider these aspects as well. It will identify those who have been negligent in their management of the project and should be held directly responsible for the tragedy.
According to experts, the tunnel route passes through highly fragile Himalayan strata, primarily composed of Dolomitic Limestone and Slate interbeds. Shear zones and weak rock mass frequently lead to sudden crown collapses, causing large structural cavities. Heavy monsoon rains trigger flash floods and severe landslides overhead. Water enters through natural rock fractures or unsealed openings from above, turning the tunnel into a high-pressure channel for sludge and debris. Problems occur when weak zones are not sufficiently stabilised via pre-grouting before structural advance.
Beyond geological hazards, operational errors pose high risks. To prevent future collapses and protect lives, the executing agencies must implement a rigorous framework of structural and managerial remedies. It is necessary to establish pipe umbrella systems ahead of the excavation face to support weak dolomitic slate zones before drilling. Specialised waterproofing and consolidating grouts to seal water-bearing faults and prevent external water from breaking into the tunnel lining are also necessary.
As experienced in the earlier Silkyara incident, smaller bypass or escape tunnels running parallel to the main headrace and tail-race tunnels are required to serve as dry, obstacle-free emergency exit routes. Thick, high-diameter structural steel pipes need to be installed along the upper crown of the tunnel to guarantee a lifeline for oxygen, food, and communication if a section gets blocked. Modern technology provides electronic groundwater pressure and rock movement sensors linked to automated alarm sirens. Continuous horizontal directional drilling (HDD) and probing 30 to 50 metres ahead of the blasting face can map hidden water pockets or cavities. Another suggestion is to situate high-horsepower, backup-powered diesel de-watering pumps every 500 metres to rapidly counter sudden surges of ingress water. These are just a few options suggested. The question is: Will the system learn the lessons and take responsibility? Or, will workers continue to lose their lives because of lack of due diligence?
