Explained: From rat-hole mining to vertical drilling — methods used at Uttarkashi tunnel
The rescue missions in Uttarkashi are currently underway, with different approaches being used to extract the 41 trapped workers stuck inside collapsed tunnel.
On the 17th day of the Uttarakhand tunnel collapse, operations were in the last phase to rescue the 41 workers trapped inside the road structure. The authorities, till now, have used multiple techniques to bring the workers out of the tunnel section.
Among the different rescue techniques used by the authorities, rat-hole mining (manual drilling) is considered to be the most dangerous and risky. Meanwhile, vertical drilling is also being conducted, while the horizontal drilling approach failed.
As the rescue operations are moving forward at a steady pace, here is all you need to know about the different drilling methods being used by agencies, and what is the difference between them.
Uttarakhand tunnel collapse: Different drilling methods
Rat-hole mining (manual drilling)
Rat-hole mining is a method of manual drilling, which is carried out by skilled workers, most common in Meghalaya. Narrow pits are dug into the ground, usually just wide enough for one person to fit into.
After digging the pits, the miner drops down into the holes using a rope and bamboo ladders. This method is usually used to extract coals, and is considered extremely hazardous. It is illegal in many countries due to increasing cases of miners dying from asphyxiation, lack of oxygen and hunger.
Uttarakhand government’s nodal officer Neeraj Khairwal made it clear that the men brought to the site were not rat-hole miners but people who are experts in the technique, news agency PTI reported.
Vertical drilling is done through a boring machine, digging straight down from the ground using electrical tools and equipment. In the case of the Uttarakhand tunnel collapse, a vertical drill has been boring into the ground and an 800-mm pipe has been inserted to bring out the trapped workers.
The vertical drilling is complete, and the rest of the soil and rubble will be cleared out via manual drilling.
Auger mining (horizontal drilling)
A horizontal auger machine or a directional drill is a specialised tool designed to drill horizontal bores or create underground tunnels without disturbing the ground. These machines are used to lay down water and gas pipes, and to dig a tunnel.
However, the auger machine in the case of the Uttarakhand tunnel collapse failed to free the trapped workers as it hit metal obstructions and eventually broke down, beyond repair.
In major progress in the Uttarakhand tunnel collapse rescue operations, the vertical drilling machine has completed the drilling of over 51 metres, with just around 56 metres left to be dug out. After this, the trapped workers will be airlifted out through buckets..
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