🏗️ Detailed Notes
1️⃣ Introduction
In longwall coal mining, the roof and floor strata undergo complex deformation due to large-scale excavation. Monitoring of strata behavior is essential for predicting roof falls, controlling convergence, and ensuring safety of miners and machinery. Strata monitoring systems (SMS) help identify stress build-up, roof movement, and ground control issues before failure occurs. DGMS mandates systematic strata monitoring under Regulation 99 of Coal Mines Regulations, 2017 and relevant circulars.
2️⃣ Objective of Strata Monitoring
- Early detection of abnormal roof movement.
- Prevention of roof and side falls.
- Optimization of support system.
- Correlation of mining geometry with strata behavior.
- Compliance with DGMS and CMR safety standards.
3️⃣ DGMS Legal Framework
| Provision | Description |
|---|---|
| CMR 2017 – Regulation 99 | Precautions against dangers from roof and sides. |
| DGMS Circular (Tech.) 04/2017 | Guidelines for strata monitoring in longwall workings. |
| DGMS Circular (Tech.) 02/2015 | Use of instruments for strata control studies. |
| CMR 2017 – Regulation 100 | Support plan approval and implementation. |
4️⃣ Parameters Monitored in Longwall Workings
- Roof convergence (vertical displacement).
- Floor heave.
- Support load.
- Stress distribution.
- Strata separation height.
- Fracture zone formation above the goaf.
5️⃣ Instruments Used for Strata Monitoring
| Instrument | Purpose |
|---|---|
| Tell-tales (Mechanical/Electronic) | Measure roof movement or separation. |
| Convergence Indicators | Measure closure between roof and floor. |
| Load Cells | Record load on supports. |
| Strain Gauges | Detect stress changes in supports. |
| Borehole Extensometers | Measure multi-point displacement of roof layers. |
| Data Loggers | Store continuous readings for analysis. |
6️⃣ Monitoring Locations
- Gate roads near the face.
- Along the longwall face (roof supports).
- At the start line and tailgate junction.
- At goaf edges and roadway intersections.
- Near geological discontinuities (faults, slips).
7️⃣ Monitoring Frequency
| Location | Frequency |
|---|---|
| Working face | Daily readings. |
| Gate roads | Every shift. |
| Goaf area | Twice per day during caving. |
| Main entries | Weekly. |
8️⃣ Data Interpretation
- Roof movement >20 mm/day → unstable condition alert.
- Convergence beyond design limit → increase support density.
- Sudden load drop → possible roof fracture or collapse.
- Data transmitted to control room for trend analysis.
9️⃣ DGMS Guidelines for Strata Monitoring
- Mine must maintain a Strata Control Cell (SCC).
- Qualified personnel must record data daily.
- Reports submitted to DGMS Regional Office monthly.
- Results used for support design optimization.
- Integration with Mine Roof Monitoring System (MRMS) recommended.
🔟 Importance of Strata Monitoring
- Prevents roof falls and fatalities.
- Ensures safe longwall retreat operations.
- Reduces production downtime.
- Helps in scientific mine planning.
- Essential for DGMS compliance and mine safety audits.
⚡ Quick One-Liners (Revision Points)
- Strata monitoring ensures roof stability.
- Regulation 99 of CMR 2017 – roof & side safety.
- DGMS Circular 04/2017 – longwall strata monitoring.
- Tell-tales and extensometers measure roof movement.
- Load cells record support load variations.
- 20 mm/day roof movement = danger.
- Convergence indicators placed in gate roads.
- Data recorded daily in longwall panels.
- Strata Control Cell analyzes readings.
- DGMS requires monthly report submission.
🧠 Descriptive Model Question & Answer
Q. Explain the importance, methods, and DGMS guidelines for strata monitoring in longwall workings of coal mines.
Answer:
Strata monitoring in longwall workings is a scientific process of measuring and analyzing the movement and stress behavior of roof and floor strata due to mining. It helps in predicting and preventing roof falls and optimizing support systems.
According to Regulation 99 of the Coal Mines Regulations, 2017 and DGMS (Tech.) Circular No. 04 of 2017, every mechanized longwall mine must implement an effective Strata Monitoring System (SMS).
Common instruments include tell-tales, convergence indicators, extensometers, and load cells. Readings are taken daily at the face, gate roads, and goaf edges. Abnormal movement or stress requires immediate reinforcement of supports.
Data collected by the Strata Control Cell (SCC) are analyzed for trends and reported monthly to DGMS. This system ensures proactive roof control, reduces accidents, and supports safe mechanized mining operations. Thus, strata monitoring is vital for maintaining operational safety, productivity, and DGMS statutory compliance in longwall workings.
🎯 25 MCQs – Strata Monitoring in Longwall Workings
Q1. Main objective of strata monitoring is to:
Q2. Regulation for roof and side safety in coal mines:
Q3. DGMS circular for strata monitoring in longwalls:
Q4. Tell-tales are used to measure:
Q5. Roof movement more than 20 mm/day indicates:
Q6. Load cells measure:
Q7. Strata monitoring data recorded by:
Q8. Borehole extensometers measure:
Q9. Monitoring frequency at face:
Q10. Support plan is prepared under:
Q11. Convergence indicator measures:
Q12. Data interpretation helps:
Q13. SCC stands for:
Q14. DGMS recommends data submission:
Q15. Sudden drop in load cell reading means:
Q16. Instrument used for stress measurement:
Q17. Caving behavior monitored in:
Q18. Longwall method involves:
Q19. Overhanging roof failure can be prevented by:
Q20. Roof fall accidents can be reduced by:
Q21. Load variation in supports is caused by:
Q22. Strata separation detection tool:
Q23. Daily readings are taken by:
Q24. Failure to monitor strata may lead to:
Q25. Strata monitoring ensures:
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