Bruce Hebblewhite (BBUGS 12 September, 2013)

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1 A review of current international thick seam mining practices and geotechnical challenges (An expanded presentation on thick seam mining, based on the Morgantown 2013 conference presentation) Bruce Hebblewhite (BBUGS 12 September, 2013)

2 International practice in underground thick coal seam extraction and related ground control challenges Professor Bruce Hebblewhite, Head, School of Mining Engineering, UNSW 32 nd International Conference on Ground Control in Mining Morgantown, West Virginia, USA 30 th July 1 st August, 2013

3 Thick seam mining - problems or opportunities?

4 Thick seam mining - problems or opportunities? well a bit of both!

5 Outline of Presentation Some definitions and terminology Evolution of the major thick seam mining methods The Australian background experience in thick seam mining - past and present Review of international operations Geotechnical risks and challenges thick seam mining Conclusions

6 PART A

7 Definitions & Terminology LTCC Longwall Top Coal Caving SPL Single Pass Longwall Thick Seams Seam thickness > 4.5m (beyond reach of current routine single pass development and extraction systems) (Note: Chinese use a height of >3.5m to define thick seam operations (Wang, 2011)

8 Evolution of major thick seam methods Historically, thick seams mined by various bord and pillar methods Hydraulic mining (HM) used in niche applications Multi-slice longwall (MSL) previously used widely in parts of Europe; and in China, until recently Conventional single pass longwalls (SPL) have been progressively stretched to suit greater face heights European caving longwall systems (CL), including soutirage, have been modifed by the Chinese, to produce the current Longwall Top Coal Caving (LTCC) system

9 Background to Australian thick seam mining

10 Historical bord & pillar thick seam mining in Australia Collinsville Moura Cessnock Muswellbrook Ipswich

11 Mining thick seams up to 10m or more, using conventional bord and pillar methods, in the New South Wales coalfields during the mid-1900s

12 Collinsville multi-slice pillar extraction trial Exposed septum wooden dowel reinforcement in lower slice

13 Collinsville multi-slice development with reinforced septum

14 9m high bord and pillar workings during the 1980s 1990s

15 Muswellbrook early 1990s

16 Seam Thickness Australian thick seam reserves 4.5m 6.0m 6.0m 9.0m >9.0m No Info (after Hebblewhite et al., 2002) Number of Sites Measured Resources (Mtonnes) 2,249 3, Measured Resources (%) Ind. & Measured Resources (Mtonnes) 7,425 8,397 1, Ind. & Measured Resources (%) TOTAL 73 6, , Seam Dip <5 deg 5 deg 15 deg >15 deg ,173 2,256 1, ,684 3,698 2, TOTAL 73 6, , Seam Depth <150m 150m 300m >300m No Info ,312 1,594 1, ,303 5,383 5, TOTAL 73 6, ,

17 Focus of Australian thick seam mining requirements Based on reserves data: Australia is abundantly endowed with thick seam reserves (+6.4 billion tonnes of measured reserves) Obligation to find safe and productive methods that are competitive with conventional height operations, in terms of: Safety Productivity Operating costs Resource recovery is important, but secondary Focus is on: 35% of reserves in the 4.5m 6m category 51% in the 6m 9m category

18 Potential thick seam mining systems extended height single pass longwall (SPL) multi-slice longwall (MSL) hydraulic mining (HM) caving longwall systems (CL), including longwall top coal caving (LTCC).

19 Previous international thick seam practices

20 Hydraulic Mining Key requirements Soft/structured coal Competent roof/floor (no slaking) Effective dip through thick seams

21 Schematic of hydraulic mining (as used in NZ)

22 Spring Creek.MPG

23 Multi-slice longwall

24 Multi-slice longwalling - using septum or artificial floor (mesh)

25 A Chinese Multi-Slice Longwall Face (in 1980s)

26 MSL support mesh laying facility

27 MSL Gate end in lower slice MSL - wire mesh contains goaf over face in lower slice

28 MSL issues No savings in gate road development Question of gate road alignment Superimposed Offset Progressively wider chain pillars Stability of septum or artificial floor/roof Working under previous goaf Water Gas Ventilation Spon com

29 Caving longwall systems

30 Longwall soutirage caving system

31 Typical soutirage support (developed in Europe)

32 Valenje system, Slovenia (for ultra-thick seams) 200m thick lignite seam Mining in 20m sub-level slices using innovative sub-level caving longwall (modified soutirage) No attempt to maintain tip to face roof or face stability Surface subsidence up to 120m

33 Valenje geology

36 Early single pass longwall (SPL)

37 Prototype 6m supports built in 1980s - problems with stability, size and operations

38 4.8m single pass longwall - West Wallsend Colliery

39 Problems with face stability on SPL

40 SPL operational limits Single Pass Longwall has been considered to be a viable option for the range of seams in the 4.5m 6m thickness category, but difficulties are often encountered due to ground conditions and equipment or operational issues (especially above 5m). For many years, 6m was considered an upper limit for SPL technology

41 Longwall Top Coal Caving (LTCC)

42 Features of LTCC method Chinese developed both the equipment and the mining system Development in China driven my legislated volumetric recovery targets 75%+ Modified from earlier soutirage method 2 nd AFC towed behind rear of supports (rather than within support, or chute to front AFC) Articulated, extendable rear canopy

43 Features of LTCC method (cont d) Productivity and safety increases Mining cost reductions Optimum cave:cut ratio = 2:1 (range is from 1:1 to 4:1) Top LTCC faces in China produce +10MTPA +20,000 t/day +75% recovery of 5m 20m thick seams

44 Typical LTCC support

45 Typical Chinese 4 leg LTCC Face Support (note articulated rear canopy)

46 LTCC Face - rear AFC

47 LTCC support rear articulated canopy, and rear AFC

48 Benefits of LTCC for Australia Operating Cost Reductions: Potentially double (or greater) longwall recoverable tonnes, per metre of gateroad development, reducing development cost/tonne significantly, and reducing potential for development shortfalls. Resource Recovery and Mine Financial Performance: A viable means of extracting up to 75% to 80% of seams in the 5m 9m thickness range. Mine Safety: Lower face heights (relative to high reach SPL) result in improved face control; improved working conditions on face and improved spontaneous combustion control.

49 LTCC resource location ( source: 2000 study) NSW LTCC resources, 25% Queensland LTCC resources, 75%

50 Design and operational issues Gate end area (face end support, equipment configurations and coal clearance) Face ventilation (gas/dust management) Caving management (sequence, recovery & dilution) Cutting sequences Overall coal clearance systems (AFC capacities and compatibility with cutting and caving sequences, BSL, panel belts and outbye coal clearance systems).

51 Coal clearance opportunities Potential for higher capacity rear AFC subject to cave:cut ratio Also consider potential use of two panel belts one in each of the maingate and tailgate to separate the coal flow from the two AFCs (only in low gas environments) This has obvious benefits and applications, particularly where the coal from the lower horizon may be of a different quality to that within the top caved coal horizon.

52 PART B

53 Current Australian thick seam mining

54 Australian thick seam longwall mines using SPL (2011/2012) (source: Australian Longwall Magazine, 2012 (Coal Services data)) Mine Depth (m) Seam Thickness (m) Mining Height (m) Shield Height (m) Shield Capacity (tonnes) Broadmeadow ,152 Carborough ,238 Downs Mandalong ,053 Moranbah ,750 North Newlands ,040 Northern North ,200 Goonyella West Wallsend

55 Australia s first LTCC faces Austar mines the 6.5m thick Greta Seam using LTCC at depths of 500m 600m +, with a cutting height of ~2.9m. Austar was the first 2 leg shield LTCC mining system in the world. During 2012/2013 both Broadmeadow and North Goonyella are introducing LTCC faces (after Moodie & Anderson, 2011)

56 Review of major international thick seam operations

57 Selection of high performance international thick seam mines (2011/2012) Mine Owner Country Depth Mining Method Mining Height Face Length Matla No. 2 Exxaro South Africa 110m SPL m 126m Daw Mill UK Coal UK 700m SPL 5.2m 357m Jining No. 3 Yanzhou China 700m LTCC Cut 3m in 7m seam 290m Dongtan Yanzhou China 710m LTCC Cut 3-3.5m in 6m seam Gaohe Shanxi Gaohe Energy China 470m LTCC Cut m in 6.5m seam Daning Daning Energy China 130m SPL m 202m Tashan Datang Tashan Coal Mine Co. China 400m LTCC Cut 3.5m in 12-20m thick seam Bulianta Shenhua China 300m SPL m 286m 223m 236m 235m

58 Matla, South Africa (SPL) 6m reach SPL supports 5.5m operating height, 2.55m collapsed 1.75m wide 1,066t support capacity 4.5m 5.0m normal working height

59 Matla operational experience Working in multi-seam environment with overlying old workings Averaging 200,000t/month Experiencing problems with lack of support rigidity at +5m height (1.75m width supports) (lemniscates twisting -> damage) Early problems with weak immediate roof -> major face falls Upper roof caving problems (dolerite and stiff sandstone) at start of panels -> windblasts Water problems (overlying goaf) Major surface subsidence issues

Matla - Monthly Operating Height (average and weekly maximum) 5.6 5.4 5.2 5 4.8 4.6 4.4 4.

60 Matla - Monthly Operating Height (average and weekly maximum) Jan-04 Feb-04 Mar-04 Apr-04 May-04 Jun-04 Jul-04 Aug-04 Sep-04 Oct-04 Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05 Face Height (m) Matla problems with face/roof stability leading to major face fall through to surface Month

61 Matla geological risk

62 2-3m subsidence troughs, with high levels of tilt and strain Major subsidence impacts over Matla Colliery, South Africa

63 Subsidence impacts on road profiles and surface water management issues

64 Matla subsidence management removal of topsoil for grouting subsidence fractures

65 Daw Mill, UK (SPL) (5.4m supports cutting up to 5.2m)

Daw Mill (face instability associated with geological structures) Production of ~ 3MTPA (15,000 tpd) Face height 4.5 5.2m 850t shields, 1.75m wide 0.

66 Daw Mill (face instability associated with geological structures) Production of ~ 3MTPA (15,000 tpd) Face height m 850t shields, 1.75m wide 0.6m coal left in roof for face stability Geology causes seam rolls and faulting (11m throw fault at time of visit) Major gateroad problems due to soft floor tailgate requires brushing up to 2-3 times

67 Daw Mill closed in early 2013 due to spontaneous combustion heating

68 Jining 3 & Dongtan, China Both mines part of the Yanzhou Group (Shandong Province) Jining 7MTPA (85% from LTCC face, averaging15,000 t/day; 6m/day retreat rate) 70% recovery from 7m thick seam Use of mid-face gate-road for services access Good caving and fragmentation

69 Jining 3 & Dongtan, China Both mines part of the Yanzhou Group (Shandong Province) Jining 7MTPA (85% from LTCC face, averaging15,000 t/day; 6m/day retreat rate) 70% recovery from 7m thick seam Use of mid-face gate-road for services access Good caving and fragmentation Dongtan 2 leg, DBT 850t shields installed in 2011 (16,000 t/day) 4 leg Chinese face mini-build on surface at time of visit Recovery up to 86% by volume Looking at increased rear AFC capacity rel. to front AFC Believe maximum optimum cave:cut ratio is 3:1 (more commonly 2:1)

70 Yanzhou Group LTCC faces (Dongtan) PA AVI

71 Maingate end support, including shields over rear AFC drive and transfer point

72 Front AFC transfer Rear AFC transfer

73 PA AVI

74 Gaohe & Daning, China Gaohe (LTCC) Near Changzhi. Shanxi Province Owned by Lu an Coal Bur./Asian-American (Banpu) JV Originally designed as 6m SPL special integrated SPL/LTCC shield designed by DBT (never built) 800 tonne LTCC shields, cutting m Face conditions contain much structure (faults and joints) Gaohe coal has Chinese cavability index (F factor) of 0.2, compared to 0.6 for Daning (SPL), but 6.0 for Bulianta (SPL)

75 Gaohe & Daning, China Gaohe (LTCC) Near Changzhi. Shanxi Province Owned by Lu an Coal Bur./Asian-American (Banpu) JV Originally designed as 6m SPL special integrated SPL/LTCC shield designed by DBT (never built) 800 tonne LTCC shields, cutting m Face conditions contain much structure (faults and joints) Gaohe coal has Chinese cavability index (F factor) of 0.2, compared to 0.6 for Daning (SPL), but 6.0 for Bulianta (SPL) Daning (SPL) SPL, 130m deep, 4.5-5m face height 790t shields, 5.5m height 2 stage face flippers essential for stability (1.8m coverage) 4MTPA (180,000t/month)

76 The super mines Tashan and Bulianta, China

77 High performance LTCC faces in China Tashan Mine, located near Datong, in Shaanxi Province, was highest performing LTCC mine in China (and hence the world), in 2011/2012. The mine was operating two LTCC faces and one conventional height longwall - total annual mine production of 23MTPA 10MTPA from each LTCC face. These were averaging 35,000 t/day, with a maximum of 50,000 t/day achieved. Overall face retreat rate was between 3m and 5m per day (face length of 235m at depth of 400m). Seam thickness12m to 20m; recovery 70% and 80% within panel; cutting height of 3.5m; web thickness of 800mm. Chinese built four leg, 1,300 tonne shields. Coal clearance by AFC capacities of 2,000 t/hr (front) and 3,000 t/hr (rear), plus a maingate belt capacity of 3,500 t/hr on a 1.4m wide belt.

78 Ultra-high SPL in China (Bulianta) An exception to the previous view of a 6m upper face height limit for SPL is the current deployment of 7m+ SPL faces in northern China Bulianta Mine located near Ordos, Inner Mongolia, owned by Shenhua Group Bulianta operates a 7m high SPL face using Chinese-built two leg 1,800 tonne capacity, 2.06m wide, 76 tonne (weight) shields 7.5m maximum support height and an operating range of 3.2m 7.1m. Web thickness is 865mm A significant feature of the shields is the three-stage flippers that provide face support to almost 60% (4m) of the face height

79 Bulianta (cont d) The total annualised mine production at the time was 30MTPA, coming from 3 SPL faces one at 7m height and two each at 5.5m height The 7m high face was in its first panel of production at the time, but was producing at a rate of 13MTPA, or 43,400t/day (highest producing longwall in the world) Face retreat rate at the time was averaging 430m/month The shearer was a 3,000kW Eickhoff SL1000, fitted with 3.5m diameter drums, capable of cutting at a speed of 14.5m/min. Coal clearance was by way of a Caterpillar 6,000t/hr AFC powered by 3 x 1.6MW drives. The maingate belt was 1.6m wide. Face stability benefits from only modest depth ( m), strong coal and minimal coal structure

80 7m high Chinese face equipment at Bulianta

81 PART C

82 Geotechnical risks & challenges thick seam mining All thick seam operations Subsidence absolute magnitude, plus extreme tilts and strains can lead to greater interaction with aquifers and surface water bodies Compared to conventional heights, thick seam mining will result in greater height of caving, potrential changes in caving/goaf mechanisms and behaviour (Murcki Staszic mine in Poland uses hydraulic fill placed behind face to reduce max. subsidence from 70% to 30% of mining thickness. Some other Polish mines also use paste fill).

83 Geotechnical risks & challenges thick seam mining (cont d) LTCC Prediction of cavability and fragmentation (empirical) (A new cavability assessment criterion for Longwall Top Coal Caving. A. Vakili & B.K.Hebblewhite. International Journal of Rock Mechanics & Mining Sciences. Vol 47, No. 8, 2010). Design and prediction using 3D numerical modelling further R & D required Other factors requiring further R & D Effect of high horizontal stress Massive strata units & periodic weighting impact (+ve & -ve)

84 Cavability Cavability is considered to be a function of several variables, primarily: Strength of the coal (UCS) Structure of the coal (cleat/vertical jointing, horizontal bedding etc) Vertical stress due to depth

85 Coal seam cavability - a function of UCS, stress and structure Strong (Greater than 25MPa), 14% Weak (less than 15 Mpa), 57% UCS range Moderate (between 15 and 25Mpa), 29%

86 UNSW empirical cavability assessment tool (TCCR) Top Coal Cavability Rating (TCCR) is an empirical technique to assess cavability of coal for LTCC mining Developed on basis of: parametric numerical modelling (DEM codes); Chinese LTCC case study back-analysis; Australian thick seam SPL case study back-analysis (with top coal in goaf) Prototype assessment tool still requires further validation, plus more detailed analysis of 3D effects, horizontal stress, massive strata effects etc. Reference: A new cavability assessment criterion for Longwall Top Coal Caving. A. Vakili & B.K.Hebblewhite. International Journal of Rock Mechanics & Mining Sciences. Vol 47, No. 8, 2010).

87 Discrete element modelling of top coal caving

88 UDEC Modelling Conventional LW v LTCC

89 Caving angle and coal thickness determine critical top coal recovery (above rear AFC)

90 TCCR Equations Where: TCR = Top Coal Recovery (%) MCD = Main Caving Distance (m) (distance from start of panel to initiate top coal caving) UCS = Laboratory uniaxial compressive strength (MPa) T = Top coal thickness (m) Jv = spacing of sub-vertical joints (m) Jh = spacing of sub-horizontal joints/bedding (m) σv = major pre-mining vertical stress (MPa) σh = major pre-mining horizontal stress (MPa)

91 Caving Classification (based on TCR & MCD)

92 TCCR Caving Classification Class Description MCD TCR I II III IV V Very weak roof Good cavability Fair cavability Poor cavability Very poor cavability <7 > >32 <39

93 Chinese LTCC Back-Analysis of TCCR

94 Other geotechnical issues - LTCC Additional support req d in face ends (larger space required for equipment) Wider installation road for longer supports Improved ability to negotiate geological structures (positive attribute) Impact of high faces on chain pillar design and gate road stability (esp. using LTCC close to face-ends) Slower retreat rates in thick seam operations may create adverse face conditions

95 Geotechnical risks & challenges thick seam mining (cont d) SPL Support design stiffness/rigidity, stability and face support/containment issues Roof stability ahead of face Face stability prediction of stability v height role of face sprags Significance of geological structure on face stability and control

96 Geotechnical risks & challenges thick seam mining (cont d) LTCC v SPL Need for geotech assessment techniques to determine LTCC cavability v SPL face stability (need better understanding of Chinese F Factor, or alternative face stability assessment) Choice between methods - function of coal strength, coal structure, depth and horizontal stress conditions

97 Conclusions LTCC and SPL methods are capable of safe, high performance extraction of seams in excess of 6m thick. Significant thick seam geotechnical challenges remain with respect to: Subsidence LTCC cavability prediction and management SPL face stability and management SPL support design

98 Thank you

99 3 rd Australasian Ground Control Conference Early November, 2014 Sydney, Australia International papers welcome Abstracts due: 15 October, 2013

Top coal caving. Tuesday 23rd October 2012: 11.45am. Chief Executive Officer. M GPO Box 358 Brisbane Qld 4001

Top coal caving. Tuesday 23rd October 2012: 11.45am. Chief Executive Officer. M GPO Box 358 Brisbane Qld 4001 Conference Presentation Top coal caving Tuesday 23rd October 2012: 11.45am Allison Golsby MAusIMM(CP), RPEQ, MEn Chief Executive Officer ngsc(min Man), MMinEng(Geomech), GDipMVent GPO Box 358 Brisbane