1️⃣ Introduction
In underground metal mines, control and removal of water is essential to ensure safe working conditions. Uncontrolled inflow can lead to inundation, roof fall, machinery damage, and interruption of production. Proper design of drainage systems, sumps, and pumps is crucial for safety and compliance with DGMS standards.
2️⃣ Sources of Water Inflow
- Surface seepage through fractures or shafts.
- Old waterlogged workings nearby.
- Percolation through joints, faults, and fissures.
- Rainwater entering through raises, winzes, or portals.
- Process or service water used for drilling, dust suppression, etc.
Regulation Reference:
👉 MMR 1961, Reg. 244 – Precautions against danger from water.
3️⃣ Estimation of Water Inflow
Accurate estimation of inflow rate is vital for designing the drainage system. Methods include:
- Empirical estimation: Based on past experience or nearby mines.
- Hydrogeological study: Using borehole data, permeability tests.
- Pumping test: Measuring steady-state inflow during trial dewatering.
- Rainfall correlation: Estimating seasonal variation of inflow.
Formula for inflow rate (approximate):
Q = K × A × (h₁ - h₂) / L
Where:
K= Coefficient of permeability (m/s)A= Area of infiltration (m²)h₁–h₂= Head difference (m)L= Flow length (m)
4️⃣ Sump Design in Underground Mines
- Purpose: To collect, settle, and store water before pumping.
- Capacity: Should store at least 4–6 hours of normal inflow.
- Shape: Rectangular or circular; with baffles for sedimentation.
- Location: Near shaft bottom or main pumping station; easily accessible.
- Depth: 2–3 m below pump suction level to prevent vortex.
- Maintenance: Regular sludge removal and cleaning.
Regulation Reference:
👉 MMR 1961, Reg. 246 – Sumps and pumping installations.
5️⃣ Drainage Galleries and Water Channels
Drainage galleries are provided along haulage levels to collect and direct water to sumps. Design features:
- Gradient: 1 in 200 to 1 in 300 towards sump.
- Lined with concrete to prevent leakage.
- Provided with side drains, cross drains, and settling chambers.
6️⃣ Pumping Arrangements
Regulation Reference:
👉 MMR 1961, Reg. 248–252 – Pumping, standby arrangements, and power supply.
7️⃣ Monitoring and Safety Measures
- Water gauges installed at shaft and sump.
- Water danger plan showing old waterlogged workings (Reg. 127).
- Automatic alarms for high water level.
- Regular pumping tests for reliability.
- Training of staff for emergency dewatering procedures.
8️⃣ DGMS & Safety Precautions
- No working below old waterlogged area unless precautions under Reg. 244 are taken.
- Boreholes should be drilled ahead when approaching suspected water bodies.
- Barriers and dams to be constructed for isolation if needed.
- Pumping capacity must be adequate for maximum expected inflow plus rainfall factor.
9️⃣ Practical Example
In Kolar Gold Fields (KGF), inflow reached 4,000 L/min at 3,000 ft depth. Stage pumping with 3 multistage pumps (350 HP each) was adopted with 3-hour storage capacity sumps.
⚡ QUICK ONE-LINERS (Revision Points)
- MMR Reg. 244 deals with precautions against danger from water.
- Minimum sump capacity = 4–6 hours of normal inflow.
- Drainage gallery gradient ≈ 1 in 200.
- Stand-by pump capacity ≥ 50% of total.
- Pumps must be capable of handling peak inflow + rainfall.
- Boreholes are mandatory when approaching waterlogged workings.
- Non-return valves prevent backflow during pump failure.
- Submersible pumps are used for local drainage.
- DGMS requires regular maintenance and testing of pumping systems.
- Emergency power supply is essential for pumping stations.
🧠 DESCRIPTIVE MODEL ANSWER
Q. Describe the design and safety considerations of water inflow and drainage systems in underground metal mines as per MMR 1961.
Answer: In underground metal mines, water inflow management is vital for preventing inundation and ensuring safe working. As per MMR 1961 Reg. 244–252, precautions must be taken against dangers from surface or underground water. The inflow is estimated using hydrogeological studies, pumping tests, and empirical data. Sumps are designed to hold 4–6 hours of inflow with sedimentation arrangements. Drainage galleries are provided with a gradient of 1 in 200 towards the sump. Pumping is done using centrifugal or submersible pumps in stages, with a standby capacity of at least 50%. Delivery lines have non-return valves and strainers to prevent damage. Automatic alarms and dual power supplies ensure reliability. Boreholes are drilled ahead of development headings near waterlogged areas. Regular inspection, maintenance, and updating of the water danger plan are mandatory. Thus, effective drainage design prevents inundation hazards and ensures statutory compliance under DGMS supervision.
🎯 Test Your Knowledge: 25 MCQs
Q1. Which regulation of MMR 1961 deals with precautions against danger from water?
Q2. Minimum sump capacity should be designed for:
Q3. Recommended gradient of drainage gallery is:
Q4. Stand-by pumping capacity must be at least:
Q5. The main pump in deep metal mines is generally:
Q6. The purpose of a non-return valve in the pump delivery line is to:
Q7. Which regulation requires provision of adequate pumping arrangements?
Q8. Boreholes are drilled ahead of workings to:
Q9. The gradient of drainage channels ensures:
Q10. DGMS requires dual feeders for:
Q11. Submersible pumps are used for:
Q12. Sump depth is generally kept:
Q13. Pump suction lines are provided with:
Q14. The main hazard of inadequate drainage is:
Q15. Water danger plans are prepared under:
Q16. The permeability coefficient in inflow calculation is denoted by:
Q17. Sump baffles are provided to:
Q18. Inflow rate is measured using:
Q19. Pump delivery lines must be fitted with:
Q20. Emergency power for pumping is ensured through:
Q21. The depth of sump below suction level is kept to:
Q22. Drainage galleries are usually located:
Q23. Main pumping station is normally installed:
Q24. Old waterlogged workings are indicated in:
Q25. Which DGMS document provides guidance on mine water control?
📚 FAQ Section
Q1. What is the minimum sump capacity required?
At least 4–6 hours of normal inflow, as per MMR 1961 Regulation 246.
Q2. Which regulation covers pumping arrangements?
Regulation 248–252 of MMR 1961.
Q3. What is the gradient of drainage galleries?
Around 1 in 200 towards the sump.
Q4. What precautions are required when approaching old waterlogged workings?
Drilling of advance boreholes and preparation of water danger plan (Reg. 127 & 244).
Q5. What is the standby pump requirement under DGMS?
At least 50% of total capacity must be standby.
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🔗 Further Reading & Related Topics
📘 Conclusion
Effective drainage design in underground metal mines ensures safety, compliance, and continuity of operations. DGMS emphasizes proper estimation of inflow, sump capacity, and pump reliability under MMR 1961 Reg. 244–252.
By mastering these concepts, mining engineers and managers can eliminate inundation risks and ensure safe mine management as per statutory norms.
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