Efforts to rescue the 41 workers trapped inside the Uttarkashi tunnel are underway. Meanwhile, vertical drilling on the hill has been stopped and manual drilling is on in the tunnel. This manual drilling is also known as 'rat-hole mining'. Rat-hole mining is considered to be one of the most dangerous and risky drilling methods. Rat-hole mining is carried out by skilled workers. In this type of method, narrow pits are dug into the ground.