Support Design During operation in UG Coal Mining Bord & Pillar Method

Support Design During operation in UG Coal Mining Bord & Pillar Method

1. 1 1 Support Design in Bord and Pillar method Presented By Dr. Rizwan Hasim Assistant Professor Department of Mining Engineering BIT Sindri 29 January 2024

2. Introduction 29 January 2024 2 Production of coal: 94% from opencast, 06% from underground. Mechanized Technology for u/g coal mine: Longwall, Bord & Pillar with continuous miner technology. Roof bolting technology is widely and successfully accepted for support design in an underground coal mine. The present practices on support design considering two major parameters such as Rock Mass Rating (RMR) and gallery size (up to 4.8m gallery width) and it has been designed for conventional mining method. Challenges: Support of higher gallery width using rock bolt during development as well as depillaring operation.

3. 29 January 2024 3 Approach for the selection of the rock bolt system Analytical Approach Empirical Approach Numerical Approach

4. 29 January 2024 4 Weak Strata Laminated Strata Individual laminations bound together to form a single beam Analytical Approach Beam Theory

5. 29 January 2024 5 Competent Strata Weak Strata Anchorage Zone Suspended layer Suspension Theory Analytical Approach

6. 29 January 2024 6 Weak Strata Fractured Rock Keying Theory Analytical Approach

7. Highly jointed, altered or weathered rock Keying Theory Analytical Approach 29 January 2024 7

8. 29 January 2024 8 Approach for the selection of the rock bolt system Analytical Approach Empirical Approach Numerical Approach The empirical assessments are based on the rock mass classification, case histories and the experience of the engineers. The following three empirical assessment systems are widely and successfully used for rockbolt design. Empirical design based on CMRI – RMR Design chart for rock bolt reinforcement based on the Q system Empirical assessments based on the rock mass classification by Bieniawski

9. 9 CMRI/ISM Geo - mechanics Classification This rock mass classification system is being regularly used by various institutes. The five parameters in this classification and their importance ratings are : Parameters Max. rating Layering 30 Structural features 25 Rock weatherability 20 Strength of the roof rock 15 Ground water seepage 10 The parameter values for the classification should be determined individually for all the rock types in the roof, up to a height of at least 2m Recommendation based on the Rock Mass Rating System RMR (Indian Condition) Empirical Approach 29 January 2024

10. 10 Rock Mass Rating (RMR) is the sum of the five parameter ratings. If there are more than one rock type in the roof, RMR is evaluated separately for each rock type, and the combined RMR is obtained as: ∑(RMR of each bed × bed thickness) ———————————————- ∑ (thickness of each bed) Combined RMR = Existing Support Design Methodology 29 January 2024

11. 29 January 2024 11 Empirical Approach Empirical design based on CMR – RMR Parameter Range of values 1. Layer thickness (cm)  Rating <2.5  0-5 2.5-7.5  6-12 7.5 – 20 13-20 20- 50  21 -26 >50 27-30 2. Structural features (index)  Rating > 14 0-4 14-11 5- 10 11-7  11-16 7-4 17-21 4-10  22-25 3. Slake durability Index (%)  Rating <60  0-3 60-80  4-8 85 – 97  9-13 97-99 14- 17 > 99 18-20 4. Strength of the rock (kg/sq.cm) Rating < 100  0- 1 100-300 3-6 300-600 7-10 600 – 900  11-13 >900 14- 15 5. Ground water seepage rate (ml/m in)  Rating >2000  0- 1 2000-200 2-4 200-20 5-7 20-0  8-9 Dry  10 RMR 0-20 20 – 40 40-60 60-80 80-100 CLASS V IV III II 1 DESCRIPTION VERY POOR POOR FAIR GOOD VERY GOOD

12. 12 For Development Workings – Bord & Pillar or Longwall Rock load In Galleries (tonnes/ Sq.m ) According to CMRR-USBM RLD = 5.7 log 10 According to Bieniaweski RLD = H-0.35CMRR+6.5 µ × B × (100-RMR) / 100 where., µ is the unit weight of rock, t/m3 , B is the roadway width, m, and F is the factor of safety and RMR is the average rockmass rating of the immediate roof after adjustment. H is depth of Cover in feet in case of CMRR USBM Kilo pounds/ sq.ft According to CMRI – ISM RMR   RLD = B × µ x (1.7 -0.037 × RMR +0.0002 × RMR 2 ) Rock load at Junction (tonnes/ Sq.m ) RLD = 5 × B^0.3 × µ x (1 – (RMR /100) 2 ) 29 January 2024 Rock load at gallery ( tonnes/ Sq.m )

13. 13 An empirical relation obtained between RMR and rock loads is: Rock load in   =   Existing Support Design Methodology 29 January 2024

14. 29 January 2024 14 Support Design in developed stage

15. 29 January 2024 15 Support Load Density at gallery and junction By CMRI RMR Classification

16. 29 January 2024 16 Flow chart for deriving RMR

17. 29 January 2024 17 Adjustment to RMR Adjusted RMR 1. Depth     Less than 250 m Nil RMR x 1.0 250-400m 10% reduction RMR x 0.9 400- 600 m 20% reduction RMR x 0.8 More than 600 m 30% reduction RMR x 0.7 2. Lateral stress     Assumed stress amount     Small 10% reduction RMR x 0.9 Moderate 20% reduction RMR x 0.8 High 30% reduction RMR x 0.7 3. Induced stresses     Stress situation :     No adjacent working in the same seam Nil RMR x 1 .0 Extraction area within 20-40 m in the same seam 1 % reduction RMR x 0.9 Extraction areas within 10-20 m in the same scam Upto 30% reduction RMR x (0.7 to 0.8) Working above with 1 0-20 m parting 10% reduction RMR x 0.9 Working above with 3 -10 m parting Upto 30% reduction RMR x {0.9 to 0.8) 4. Method of excavation     Continuous miner 10% increase RMR x 1.1 Undercut and blasting Nil RMR x 1.0 Blasting off -the-solid 10% reduction RMR x 0.9 5. Gallery span     Less than 4.5 m Nil RMR x 1.0 4.5-6.0 m 1 0 – 20% reduction RMR x (0.8 to 0.9) Adjustment Factors for RMR Paul Committee Report, 1988

18. 29 January 2024 18 Case Study (Empirical Approach) Name of Mine Monnet Ispat Coal Project, Raigarh Type of Immediate Roof Medium to fine grain Sand stone Gallery width 4.5 Working height 2.5 Pillars Size 40×40 m center to center Depth 60m Seam Name II Density of Sandstone 2.07 t/m2 Density of Coal 1.4 t/m2 Anchorage Strength 12 t

19. 29 January 2024 19 Case Study (Empirical Approach)

20. 29 January 2024 20 Case Study (Empirical Approach)

21. 29 January 2024 21 Case Study (Empirical Approach)

22. 29 January 2024 22 Approach for the selection of the rock bolt system Analytical Approach Empirical Approach Numerical Approach

23. 29 January 2024 23 Case Study (Numerical Approach)

24. 29 January 2024 24 Case Study (Numerical Approach)

25. 29 January 2024 25 Roof – Bolt - Grout Interaction Bolt-Rock interaction model (after Peng and Guo , 1992)

26. THANK YOU 29 January 2024 26