Why is it in the News?

Experts in Uttarakhand have resorted to ‘rat-hole’ mining to help rescue 41 workers trapped inside the collapsed Silkyara tunnel.

Context:

• Rat hole mining, a controversial and outlaw mining practice is back in the spotlight nearly 9 years after it was banned by the National Green Tribunal (NGT) over severe environmental impacts and unsafe labour conditions.
• The rat hole mining technique is being used to extract the 41 construction workers trapped inside a collapsed Uttarakhand tunnel after modern machinery failed to execute the rescue operation.
• The attempt to free 41 trapped workers in the collapsed Silkyara-Barkot tunnel encountered a significant setback as the auger joint of the debris-drilling machine broke.

What is Rat-hole Mining?

• Rat hole mining is a method of extracting coal from narrow, horizontal seams, prevalent in Meghalaya.
• The term “rat hole” refers to the narrow pits dug into the ground, typically just large enough for one person to descend and extract coal.
• Once the pits are dug, miners descend using ropes or bamboo ladders to reach the coal seams.
• The coal is then manually extracted using primitive tools such as pickaxes, shovels, and baskets.
• The rat-hole mining is broadly of two types.
• The first type is a side-cutting procedure, in the side-cutting procedure, narrow tunnels are dug on the hill slopes and workers go inside until they find the coal seam.
• The coal seam in the hills of Meghalaya is very thin, less than 2 m in most cases.
• In the other type of rat-hole mining, called box-cutting, a rectangular opening is made, varying from 10 to 100 sqm, and through that a vertical pit is dug, 100 to 400 feet deep.
• Once the coal seam is found, rat-hole-sized tunnels are dug horizontally through which workers can extract the coal.

Environmental and Safety Concerns Associated with Rat-hole mining:

• Rat hole mining poses significant safety and environmental hazards.
• The mines are typically unregulated, lacking safety measures such as proper ventilation, structural support, or safety gear for the workers.
• Additionally, the mining process can cause land degradation, deforestation, and water pollution.
• This method of mining has faced severe criticism due to its hazardous working conditions, environmental damage, and numerous accidents leading to injuries and fatalities.
• Despite attempts by authorities to regulate or ban such practices, they often persist due to economic factors and the absence of viable alternative livelihoods for the local population.

When and Why was Rat-hole Mining Banned?

• This rat-mining method has faced severe criticism due to its hazardous working conditions, environmental damage, and numerous accidents leading to injuries and fatalities.
• Experts have opined that the mines are typically unregulated, lacking safety measures such as proper ventilation, structural support, or safety gear for the workers, thereby creating a rather harmful environment for the rat-miners.
• The National Green Tribunal (NGT) banned the practice in 2014 and retained the ban in 2015.
• The NGT observed, “It is also informed that there is umpteen number of cases where by virtue of rat-hole mining, during the rainy season, water flooded into the mining areas resulting in the death of many individuals including employees/workers."

How Rat-hole Mining has Helped in Uttarakhand Tunnel Rescue Operation?

• The state-of-the-art American auger machine drilled roughly 47-48 meters of a horizontal tunnel.
• After that, it’s driller tool broke inside the drilled passage and authorities said that the damage was beyond repair.
• The rescue teams then resorted to manual drilling – a safer but time-consuming option. However, they brought in a team of rat hole mining experts who completed the remaining task in less than two days.
• The rat hole miners went inside the steel pipe being pushed inside the rubble through which trapped workers were pulled out and drilled a horizontal passage.
• The process was somewhat similar to the digging of a narrow tunnel for coal mining.

What are the Other Methods Used to Rescue the Trapped Workers in the Silkyara Tunnel?

• Vertical drilling: 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 had been boring into the ground and an 800-mm pipe had been inserted to bring out the trapped workers.
• 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.

What is a Horizontal Auger Machine?

• A horizontal auger machine, also known as a horizontal boring machine or directional drill, is a specialized tool designed for creating horizontal bores or underground tunnels without causing surface disruption.
• It typically features a rotating helical screw blade, referred to as an auger, attached to a central shaft or drill, facilitating penetration through rotation.
• Applications: Widely utilized in construction, utility installations (such as laying pipes or cables), and various infrastructure projects.
• Working Mechanism: Positioned at the starting point of the bore, often on the surface, the machine comprises a drill head with an auger or a drill string.
• The rotating auger at the front of the machine cuts through soil, rock, or other underground materials.
• The rotation is powered by hydraulic or mechanical systems.
• As the auger progresses, it removes the material from the tunnel.
• The removal process is usually facilitated by a drilling fluid or mud pumped through the drill string.
• The drilling fluid serves multiple purposes, including lubricating the drilling process, cooling the cutting head, and transporting excavated material back to the surface.