Productivity Improvement in Underground Coal Mines - A Case Study

Productivity Improvement in Underground Coal Mines – A Practical Case Study

Improving productivity has become one of the biggest challenges for today’s coal industry. With rising competition, fluctuating market prices, and constant pressure to maintain healthy profits, mines can no longer afford waste, inefficiency, or under-utilised equipment. The only sustainable way forward is to cut production costs by raising productivity, efficiency, and equipment effectiveness.

This detailed post is based on a real case study conducted at Digwadih Colliery (Jamadoba Section, Jharia Division, Tata Steel Ltd., Dhanbad, Jharkhand). The mine produces washed prime coking coal from Seam 9 and Seam 11 using the traditional bord-and-pillar method. Coal is extracted by drilling and blasting, loaded by Side Discharge Loaders (SDLs), and transported through chain and belt conveyors to the Jamadoba Coal Preparation Plant.

Why Underground Coal Mining in India Needs Urgent Productivity Improvement

India is the world’s third-largest coal producer, yet only about 15% of its total coal comes from underground mines. In comparison, China produces nearly 95%, USA about 33%, and Australia around 20% from underground operations. More than 90% of India’s underground production still relies on the bord-and-pillar method.

The average Output per Manshift (OMS) in Indian underground mines has remained stuck between 0.70–0.77 tonnes for several years — far below international standards. Near-surface reserves are depleting fast, land acquisition for opencast mining is becoming extremely difficult, and the industry target is to increase the underground share to 30% by 2030.

Fig. 1 – Trend of coal production in million tonnes from CIL mines (1974–75 to 2011–12)

While opencast mining has seen major technological advancements, underground mining has remained sluggish. Efficiency growth (not just new machines) has been the real driver of productivity improvement in underground mines. This means better utilisation of existing equipment, smarter management of the production cycle, and elimination of avoidable delays.

The Digwadih Colliery Case Study

Digwadih Colliery is a typical bord-and-pillar mine. Narrow galleries (bords) are driven into the coal seam, pillars are formed, and later extracted during depillaring. Side Discharge Loaders (SDLs) are the main production machines. They load the blasted coal onto chain conveyors, which then feed the main belt conveyor system.

Fig. 2 – Schematic layout of a bord and pillar mine with SDL and conveyor system

Time studies clearly revealed the major bottlenecks:

• Excessive travelling (lead) distance of the SDL
• High production losses due to SDL downtime
• Bad roof conditions
• Frequent stoppages of belt conveyors
• Wastage of manpower in handling the SDL trailing cable
• Frequent cable damage leading to machine breakdowns

Monthly production-loss data showed that SDL-related issues were the single largest contributor to lost production.

Three Key Factors That Decide Mine Productivity

Almost every productivity problem in an underground coal mine falls under one of these three areas:

1. Cycle of Operations – Dewatering, face dressing & supporting, drilling, charging, blasting, fume clearance, loading, and conveying.
2. Machine Efficiency – Availability, utilisation, and reliability of SDLs and conveyors.
3. Manpower Management – How people are deployed, how idle time is controlled, and whether skilled operators are freed from non-productive work.

Lean manufacturing principles fit perfectly here: identify waste, coordinate resources properly, and deliver only what the next process needs, when it needs it.

The Most Powerful Lever – Controlling SDL Lead Distance

Lead distance (the distance the SDL travels from the face to the chain conveyor) is one of the strongest productivity levers available. Studies showed that keeping the lead distance between 6 to 9 metres (and never allowing it to exceed 18 metres in any shift) gives the best results.

Reducing the average lead distance from 30 m to 15 m produces a dramatic reduction in cycle time and a clear increase in tonnes per SDL per day. Every unnecessary metre of travel adds seconds that multiply across dozens of cycles and several machines every shift.

Simply controlling lead distance can improve SDL productivity by 20–40% depending on the starting baseline.

Solving the SDL Cable Handling Problem

One of the most practical findings of the study was the serious wastage caused by poor trailing cable management. Someone has to constantly “tail” the cable, the crawler often rides over it, and expensive cables get damaged frequently — leading to breakdowns and lost production.

Three simple, low-cost methods were proposed:

Method 1 – Weight Tensioning System
The trailing cable is kept under controlled tension using a simple system of weights. The cable stays clear of the floor and the SDL path, eliminating both manpower wastage and damage risk.

Method 2 – Spring-Assisted Side Wall Guides
Springs or elastic supports fixed to the gallery walls keep the cable elevated and properly guided. The SDL can move freely without the cable becoming an obstacle.

Method 3 – Overhead / Side Wire Guidance
A light wire or rope system supported at intervals allows the cable to slide smoothly as the machine advances or retreats.

Any one of these methods frees operators for productive work, reduces unplanned downtime, and protects costly cable stock.

Combining Improvements – Real Results

The researchers tested several combinations of changes (shorter lead distance, better blasting practice, improved face preparation, cable handling fixes, etc.). The best combined package reduced the average cycle time from 253 minutes to about 239 minutes and increased per-SDL production by nearly 23%.

With five SDLs working, the daily output gain becomes substantial — without buying a single new machine.

Practical Takeaways for Any Underground Mine

• Measure actual cycle times and lead distances regularly. What gets measured gets managed.
• Keep SDL lead distance short and consistent. Move the chain conveyor forward as soon as conditions allow.
• Eliminate cable-handling waste using one of the three simple mechanical solutions.
• Stagger or overlap shifts so that face preparation and machine work do not leave expensive equipment idle.
• Treat roof control and conveyor reliability as productivity issues, not just safety issues.
• Focus first on low-cost, high-impact changes. Technology upgrades can come later.

Many of the improvements suggested require only modest investment and disciplined supervision. The payoff — higher OMS, lower unit cost, and better equipment utilisation — is almost immediate.

Final Thoughts

Underground coal mining in India still has enormous headroom for improvement. By attacking everyday wastes in the production cycle, managing machines more intelligently, and freeing people from non-value-adding work, mines can raise productivity significantly while remaining competitive on cost and safety.

The Digwadih experience clearly shows that the solutions are already within reach — they simply need to be recognised and applied consistently.

If you operate or advise an underground coal mine using SDLs or similar equipment, start today by mapping your own cycle times and lead distances. The numbers will almost certainly point to quick and valuable wins.

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Based on the research paper “Productivity Improvement in Underground Coal Mines – A Case Study” by Devi Prasad Mishra, Mamtesh Sugla and Prasun Singha, published in Journal of Sustainable Mining (2013).