2013/09/03 On 21 January 1960, the Coalbrook North Mine collapsed. 437 miners perished in the event. It still is the single most tragic accident Lessons From Coalbrook in South African mining. Presentation to SACMA 22 August 2013 It resulted in a research drive that put South Africa at the forefront of mining science for several decades. Prof Nielen van der Merwe On 21 January 1960, the Coalbrook North Mine collapsed. Base evaluation on Coalbrook disaster 437 miners perished in the event. It still is the single most tragic accident 1. What happened at Coalbrook? in South African mining. 2. What were the unknowns at the time? 3. How were they addressed? It resulted in a research drive that put 4. Would the new technology have prevented South Africa at the forefront of mining science for several decades. the accident? 1. What is the current situation? 53 years later - 2. How do we match up for the future? what did we learn? Coalbrook Coalbrook Geology and Dimensions Production build-up 3000000 Shale and Sandstone 60 m 2500000 Dolerite 40 m 2000000 Tonnes Produced Power Station 2 m Coal No 3 Seam Contract 1500000 140 m Shale and Sandstone 6 m Coal No 2 Seam 1000000 Shale and Sandstone 500000 0 – 3 m Coal No 1 Seam Lava 0 1905 1915 1925 1935 1945 1955 1965 Year 1
2013/09/03 Coalbrook Coalbrook The Pre-1932 Period The period 1932 - 1950 6.7 m Bords 24.4 m Centres 2.4 m High 24.4 m Barriers 6.7 m Bords Panels North 19.8 m Centres 2.4 m High 18.3 m Barriers Development West Shaft complex Panels South Coalbrook Coalbrook The Post 1950 Period Coalbrook by the end of 1959 1950 - 1959 6.7 m Bords 6.7 m Bords 1905 - 1932 19.8 m Centres 19.8 m Centres 4.3 m to 5.5 m High 4.3 m to 5.5 m High 6.7 m Bords 13.1 m Barriers 24.4 m Centres 13.1 m Barriers 2.4 m High 24.4 m Barriers 10 Years 28 Years 18 Years 1932 - 1950 6.7 m Bords 19.8 m Centres 2.4 m High 18.3 m Barriers Coalbrook Coalbrook Coalbrook by the end of 1959 +/- 1955, Steart: • Competent planning, etc Dimension Changes Over Time • ….poor strength of no 2 Seam… 30 • Extraction < 40% 1905 - 1932 1932 - 1950 • Height 2.9 m 1950 - 1960 25 • “Adequate barriers…” 20 15 1957, Inspector of Mines: 10 • Bord width – 6.1 m • Height 4.3 m 5 0 Bords Centres Height Barriers 2
2013/09/03 Coalbrook Coalbrook The 1959 Section 10 Experiment Following the successful Experiment…… 6.7 m Boards 19.8 m Centres • Section 10 continued top coaling southward 4.3 to 6.1 m High • Elsewhere top coaling on advance to 4.3 m 4 m by 2 m Dummies cut in pillars Visual monitoring • Mining either side of experiment Nothing Happened • Centres 18.3 m • Barriers 12.2 m This continued to December 1959 Coalbrook Coalbrook 28 December, 1959…… 11 January, 1960…… Inspector visited mine Pillar collapse, old Section 10 No signs of instability Wind blast, 1 injury Collapse not reported Afterwards, nothing….. Everything back to normal Shaft Shaft Coalbrook Coalbrook 21 January, 1960, afternoon shift…… 21 January, 1960, 16:00…… Cracking noises from Section 10 Two sections withdrew Windblast Men working Men working Shaft Shaft Men working Men working 3
2013/09/03 Coalbrook Coalbrook 21 January, 1960, +/- 17:00…… 21 January, 1960, +/- 19:00…… Mine Overseer, Acting Manager inspect workings Increasing noise from Section 10, methane emissions Noises only from Section 10 Repair crews left “at the double” No CO Overtaken by hurricane “Weight had come off…..safe to replace seals….” General exodus Shaft Shaft Men working Men working Coalbrook Coalbrook 21 January, 1960, +/- 19:00…… 21 January, 1960, by 19:20…… Shaft Shaft Men working Men working Coalbrook Coalbrook The Collapsed Area Area 2 Area 1 4
2013/09/03 The Unknowns The Unknowns Area 1 Area 2 Reduced span? Dolerite bridging? Small pillars, top coaling, INTACT Small pillars, top coaling, COLLAPSED Small pillars, no top coaling, COLLAPSED Influence of barriers? Small pillars, no top coaling, INTACT The Unknowns The Unknowns Barriers The Four Main Unknowns Some barriers failed, others survived… How big is big enough? 1. Pillar strength 2. Barrier strength 3. Loading 4. Role of overburden(dolerite?) Major research effort over next few decades Several scientists migrated to South Africa Birth of COMRO Addressing the Unknowns: Pillar Strength Addressing the Unknowns: Pillar Strength The Pioneering Work The Refinements 1980 4 A Bieniawski: Wagner: w e = C Large scale tests � � 1982 � � � � ε b � � w R b R � � � � 0 � � σ = 2 . 76 + 1 . 52 Salamon: σ = k � � − 1 + 1 s s a ε � � � � h V � R � � � � � 0 1991 � � � � 2 . 5 0 5933 . � � � � 5 0 . 5933 R σ = � � � � − � + � Madden: k 1 1 s 0 . 0667 � � V � 2 . 5 � 5 � � � � � � Salamon and Munro: 1991 w 0 . 63 Back analysis Madden: σ s = 5 . 24 0 . 78 h 0 . 46 w σ s = 7 . 176 1993 0 . 46 0 . 66 w h Van der Merwe: σ s = 4 . 5 0 . 66 h 2003 w Van der Merwe: σ = 3 . 5 s h 5
2013/09/03 Addressing the Unknowns: Pillar Strength Shift Toward Time Shift Toward Time 1 � � d 1 − x Van der Merwe: T = � � � x � mh [ ] 0 , 333 = − 2 d w 0 , 00714 S HhC m Frequency of Predicted vs Actual Life Rate vs Time 30 0.9 0.8 Average Scaling Rate (m/year) 25 0.7 Measured Data Predicted Number of Failures 0.6 20 Predicted Data Actual 0.5 0.4 15 0.3 10 0.2 0.1 5 0 0 10 20 30 40 50 60 0 Age of Pillar (Years) 0 20 40 60 80 100 120 Life (Years) Addressing the Unknowns: Pillar Load Addressing the Unknowns: Overburden Tributary Area Theory Galvin (1983) + 2 0 . 025 H ( w B ) σ = Elastic Plate Theory L 2 w 0 . 025 H ( w + B )( w + B ) Van der Merwe (1995) σ = 1 1 2 2 L w w 1 2 Modified Key-block ( w + B )( w + B ) [ ( ) ] σ = 1 1 2 2 0 . 025 H − T + 0 . 03 T β ( ) L L c = 2 T k + + 2 H − D ) tan φ w w 1 2 D c − b γ k λ d − β = γ tan θ 2 Roberts et al (2001) m • TAT not strictly valid Dolerite only addressed • Several unquantifiables • Can of worms • Stick to TAT Addressing the Unknowns: Barriers Assessing Progress: Coalbrook Pillar Stability SF = 1.0 SF = 1.0 Esterhuizen (1992) SF = 0.6 SF = 0.6 Suggested using Wilson (1983) and 2-D models SF = 1.6 SF = 1.0 SF = 2.3 Roberts and van der Merwe (2005) SF = 1.4 Hybrid ELFEN code No easy to use formula yet SF = 2.1 SF = 1.3 SF = 1.1 SF = 0.7 SF = 1.7 SF = 1.0 Blue: Salamon and Munro Red: van der Merwe 6
2013/09/03 Assessing Progress: Coalbrook Assessing Progress: Coalbrook Barrier Strength Overburden Behaviour ? ? Assessing Progress: Coalbrook Assessing Progress: Coalbrook Anomalies can be explained conceptually Pillar Loading Not easily quantified……………… ? Assessing Progress: Pillar Strength Springlake Colliery 2001 Failures continue but at reduced rate Before 1967: 27 failures Expected (mined after 1967): 114 Actual (mined after 1967): 23 Sobering Statistics – Failed Pillars: Age prior to 1967: 8.2 years Age after 1967: 21.3 years SF of failures mined before 1967 = 1.0 (0.9) SF of failures mined after 1967 = 1.7 (1.8) Are we getting less or is it just taking longer? Disaster not repeated – could it have been? 7
2013/09/03 Welgedacht Colliery 1998 Welgedacht Colliery 1998 Collapsed pillars, Welgedacht Shuttle car extraction, Welgedacht Assessing Progress: Deeper Issues Disturbing Parallels Between Coalbrook 1960 and Industry 2010 Nature of the experiment • born in reaction to restrictions • desperate for coal • Increasing coal demand for electricity • no measurement, ears and eyes only • New pitroom not ready (Waterberg) • “success” after 3 months • BUT: trigger only, small pillars, greater height for 11 years • Technology lagging • Researchers not available Advice not heeded • Funding decreasing +/- 1955, Steart: • Competent planning, etc • ….poor strength of no 2 Seam… • Extraction < 40% • Height 2.9 m • “Adequate barriers…” SF would have been 1.6 (2.5) In quest for coal, Coalbrook moved beyond knowledge 8
2013/09/03 Urgent Coal Mining Research Needs South Africa needs a strong mining industry: safe, productive, profitable Current mining Extraction of small, shallow pillars – increase life of Witbank field “What saves a man is to take a step. Then another step. Time effect on pillar stability – confirm and refine existing It is always the same step, but you have to take it.” Pillar loading, overburden role Antoine de Saint-Exupéry Barrier strength and spacing Waterberg preparation What are the host rock characteristics? We need to do the research How do we mine thick, deep seams? How do we mine using less water? How will we support the roof? What equipment will we need? Just this once, let us learn from history………… Current Coal RE Doctoral Research at Wits Extraction of small, shallow pillars – Sandor Petho (part time) Squat pillar review – Markus Matthey (full time) Remember Coalbrook Vaal Basin strength – Gift Makusha (part time) Waterberg characterisation – Lelani Prinsloo (part time) Time effect on pillar stability – Self Probability of failure – Self 9
Recommend
More recommend
