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The effect of seam dip on the application of the Longwall Top Coal Caving method for inclined thick seams By Dao Hong Quang B.E. (Hons) in Mining Engineering, University of Mining and Geology, Vietnam M.E in Mining Engineering, University of New South Wales, Australia A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Mining Engineering The University of New South Wales Sydney, Australia March 2010 ORIGINALITY STATEMENT I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institu- tion, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged. Signed . Date . i Abstract This thesis presents the results of research into the potential of underground mining methods applicable to inclined thick seams in the Quangninh coalfield, Vietnam. For this research, an inclined thick seam is defined as a coal seam with a thickness of greater than 3.5 metres, and a seam dip ranging from 15 to 35 degrees. This research further investigated the feasibility of applying the most appro- priate underground methods for the extraction of inclined thick seams in the Quangninh coalfield, in order to meet the increasing demand for coal products and standards of safety management. The primary objectives of this research are: 1. to investigate the most suitable underground methods applicable to inclined thick seams in the Quangninh coalfield; 2. improve understanding of the opera- tional and geotechnical issues associated with the application of chosen methods in thick seams with steeply dipping conditions. From a risk and operational assessment, the Longwall Top Coal Caving (LTCC) method is considered the most appropriate method for the Quangninh mining sit- uation. The LTCC method, original referred to as the \soutirage" method, offers great potential for the efficient extraction of thick seams by caving coal from the upper section during the mining of the lower section. This significantly reduces the development cost per tonne of coal product. Compared to High reach Single Pass Longwalling, the LTCC method offers a lower face height, which results in smaller and less expensive equipment, and better face conditions. The output of coal per metre of gate road development from the LTCC method is much more than the multi-slice longwal method, and the entry layout of the LTCC method ii iii is much simpler than that of the multi-slice longwall method. Results from this study indicated that for the extraction of an inclined thick seam, the face retreating along the strike has better operational advantages and has better cavability than the face retreating updip or downdip of the seam. The major operational issues of the LTCC method when extracting inclined seams are: the stability of the support, the difficulties of installation and transport in steeply dipping conditions, and the difficulties in roof control at the transition between face ends and the gateroads. In terms of geotechnical issues, better cavability of the top coal is anticipated for flat coal seams compared to inclined seams. In addition, the chain pillar for flat coal seams is subjected to a higher vertical stress distribution than that of inclined ones. An improved cavability assessment (CPI) method for the categorisation of the cavability of the top coal with four categories, ranging from 1 (excellent cavability) to 4 (very poor cavability), was suggested to assist underground mining design for predicting the cavability of the top coal of an inclined LTCC face. The cavability assessment method was conducted by numerical analysis combined with back analysis from the database obtained from past LTCC practices. Acknowledgements I would like to extend sincere thanks to following persons and organizations for providing assistance and guidance during the process of research and writing of this thesis: Professor Bruce Hebblewhite, my supervisor, for his assistance and construc- tive criticism during my research and his support and encouragement which made the completion of this dissertation possible. Dr. Yuejun Cai and Dr. Rudrajit Mitra, my co-supervisors, for assistance in the numerical modelling, providing valuable comments and suggestions on my work. Dr. Serkan Saydam, the postgraduate co-ordinator of the School of Mining Engineering, for his organisational assistance during the time of my research at the School. Ms Bronwen Phillips and Mr Ed Malone for editing this thesis and provid- ing comments during the write-up. Dr. Abouze Vakili for his comments and discussion of the results for my cavability criterion development and modelling. Associate Professor David Laurence for his help, encouragement during my study. Dr. Nguyen Anh Tuan and staff members at the Institute of Mining Science and Technology (IMSAT), Vietnam, for their assistance with compiling geotech- nical data of the Quangninh coalfield, and for their constructive criticism. The Ministry of Education and Training, Vietnam, through MOET scholar- ship, the University of New South Wales through Top-Up scholarship, and the School of Mining Engineering through the grant of Professor Bruce Hebblewhite. Staff members of the School of Mining Engineering for their individual help, iv v encouragement and providing both resources and friendship during my time with the school. Canh Quang, Danh, Dat, Kha and Cuong for their support and friendship throughout my stay in Australia. Finally, to my family for their constant love and support, and for encouraging me to pursue higher studies. The deepest appreciation is reserved for my mother Du Thi Nguyen, my wife Ly Thi Ninh, and my daughter Trang Ninh Dao whose love, understanding and caring sustained me throughout my study. Table of Contents Abstract ii Acknowledgements iv Table of Contents vi List of Figures xii List of Tables xix 1 Introduction 1 1.1 Background .............................. 1 1.2 Research objectives .......................... 2 1.3 Thesis structure ............................ 3 1.4 The contributions of the research .................. 5 1.5 Published papers ........................... 6 2 Thick Seam Mining Challenges in the Quangninh Coalfield 8 2.1 Introduction .............................. 8 2.2 General geology of the Quangninh coalfield ............. 9 2.2.1 Geological structure of the Quangninh coalfield . 10 2.2.2 Structure of tectonic setting . 14 2.2.3 Hydrology setting ....................... 15 2.2.4 Coal quality .......................... 15 2.2.5 Analysis of thick seams reserves in Quangninh . 16 vi vii 2.2.6 Assessment of geological conditions in the Quangninh coal- field .............................. 21 2.3 Thick seam mining challenges in Quangninh . 22 2.3.1 Status of thick seam mining in Quangninh . 23 2.3.2 Demands for coal production and the availability of coal reserves in Vietnam ...................... 29 2.3.3 Discussion ........................... 30 2.4 Conclusions .............................. 32 3 Potential Underground Thick Seam Mining in the Quangninh Coalfield 35 3.1 Introduction .............................. 35 3.2 Literature review ........................... 36 3.2.1 The Room and Pillar method . 37 3.2.2 High reach Single Pass Longwall method . 41 3.2.3 Multi-slice Longwall method . 43 3.2.4 Hydraulic mining method . 47 3.2.5 Longwall Top Coal Caving method . 49 3.3 Potential thick seam mining methods applicable to Quangninh's conditions ............................... 53 3.3.1 Room and Pillar and Blasting Gallery methods . 55 3.3.2 High reach Single Pass Longwall method . 59 3.3.3 Multi-slice Longwall method . 64 3.3.4 Hydraulic mining ....................... 66 3.3.5 Longwall Top Coal Caving . 69 3.4 Conclusions .............................. 72 4 Operational issues for the extraction of inclined thick seams by the LTCC method 75 4.1 Introduction .............................. 75 4.2 Face directions in inclined seams ................... 76 4.3 LTCC face equipment ........................ 80 viii 4.4 LTCC supports for steeply dipping seams . 91 4.4.1 Support tilting ........................ 91 4.4.2 Slippage of equipment at an inclined longwall face . 94 4.4.3 Support transport ....................... 98 4.5 Transition between the face ends and the gateroads . 99 4.6 Conclusions .............................. 102 5 Effect of Seam Dip on the Cavability of Top Coal in the LTCC method 105 5.1 Introduction .............................. 105 5.2 Literature review . 106 5.2.1 Coal strength . 109 5.2.2 Discontinuities . 111 5.2.3 The cover depth of the seam . 115 5.2.4 Overlying strata . 118 5.2.5 Top coal thickness . 121 5.2.6 Pre-mining stress regime . 122 5.2.7 Moisture sensitivity . 124 5.2.8 Discussion . 125 5.3 Numerical analyses for underground mining . 125 5.3.1 Types of numerical methods . 127 5.3.2 The numerical methods used in the current study . 127 5.4 The effect of face orientation on the cavability of inclined thick seams128 5.4.1 Scope of the modelling . 128 5.4.2 Mining geometry . 129 5.4.3 Material properties and constitutive models . 130 5.4.4 Simulation of face extraction and top-coal caving . 132 5.4.5 Discussion of numerical modelling results . 134 5.5 Conclusions .............................. 144 ix 6 Caving mechanism of the Top Coal in the LTCC method for Inclined Thick Seams 146 6.1 Introduction .............................. 146 6.2 Mining geometry . 147 6.3 Material properties and constitutive models . 149 6.4 Simulation of face extraction and top coal caving . 150 6.5 Discussion of the numerical modelling results .

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