Another consideration as stated by ML Sharma, a professor from IIT Roorkee, is the presence of undetected cavities in the rocks, gaps between these mountain rocks. These cavities naturally weaken such areas, increasing the risk of landslides. These are 2 possible causes, but we can only speculate right now and the definitive reason will be established only after the completion of investigation reports.
There are two main approaches to constructing a tunnel construction in mountainous terrain, the first is the Drill And Blast Method (DBM), and the second is by using a Tunnel Boring Machine (TBM). The former involves drilling holes in stones, placing explosives, and literally blasting the rocks. It’s as if a small bomb is detonated from inside the rocks. It is the simple and traditional approach.
Using the tunnel boring machine is a more expensive but safer alternative. The machine creates a hole in the rocks with a rotating head, and precast concrete segments are then installed.
