What's the rat-hole mining technique used to rescue trapped workers in Uttarkashi tunnel?

Rescue experts in Uttarakhand have turned to the rat-hole mining technique to extract the 41 trapped workers from the Silkyara tunnel in Uttarkashi.

Despite facing several setbacks in the rescue efforts over the past few days, engineers have now opted for manual drilling to complete the excavation and rescue the workers.

A team of workers began removing the muck by hand using the rat-hole mining technique on Monday while 800-mm diameter pipes were being pushed through the rubble by an auger machine, reported PTI

The 41 workers have bee trapped inside the collapsed Silkyara-Barkot tunnel in Uttarkashi since November 12.

What is this technique?

• It is a common method of manual drilling where rat-hole-sized openings are manually dug, allowing enough space for one person to enter.

• Widely used in Meghalaya, this technique is commonly employed for coal extraction from mines.

• In Uttarakhand, experts are manually digging holes, extracting debris from the pipes, and then using these openings to extract the trapped workers.

• These rat-holes can be dug both vertically and horizontally.

• It is categorised into two primary methods: Side cutting and box-cutting.

• Side-cutting involves creating narrow tunnels on hill slopes where workers venture inside until they reach a coal seam, commonly utilized in Meghalaya for coal extraction.

• In box-cutting, vertical pits of 100 to 400 feet deep are dug, followed by horizontal digging as necessary to access the coal seam.

Risks associated with this procedure

• The rat-mining technique, though traditional, poses risks and is banned in many countries due to fatalities caused by asphyxiation, lack of oxygen, and hunger among miners.

In India, this practice is regulated, yet it persists due to economic reasons and limited alternative methods.

Progress update: Vertical drilling completion

• Vertical drilling in Uttarkashi is nearly finished, and an 800 mm pipe has been inserted to facilitate the workers' extraction.
• The remaining soil and rubble will be manually removed through drilling.
• Rat-hole mining was adopted as a last resort after the Augur machine faced obstacles, damaging its equipment upon contact with metals.
• Currently, drilling has reached approximately 51 meters vertically, with only 56 meters left to excavate.
  Following this, workers will be lifted out using buckets.

Furthermore, CM Pushkar Dhami has assured that all trapped workers will soon be rescued by the skilled engineers.