Stability Analysis of a Longwall Mining in Narva Oil Shale Mine
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STABILITY ANALYSIS OF A LONGWALL MINING IN NARVA OIL SHALE MINE Ott Oisalu Taavi Lõhmuste Civil Engineering, master's level (120 credits) 2017 Luleå University of Technology Department of Civil, Environmental and Natural Resources Engineering LULEÅ UNIVERSITY OF TECHNOLOGY Civil engineering X7003B Taavi Lõhmuste, Ott Oisalu STABILITY ANALYSIS OF A LONGWALL MINING IN NARVA OIL SHALE MINE Master’s degree project Supervisor: Dr. David Saiang External supervisor: Dr. Oleg Nikitin Luleå 2017 2 TABLE OF CONTENTS Abstract ........................................................................................................................... 5 Acknowledgement .......................................................................................................... 7 1. Introduction ................................................................................................................. 8 1.1 Background ........................................................................................................... 8 1.2 Project organisation .............................................................................................. 9 1.3 Tasks of the project ............................................................................................. 10 2. Methodology ............................................................................................................. 11 2.1 Baltic Basin oil shale resources .......................................................................... 11 2.1.1 Characterization of oil shale in Baltic basin ................................................ 11 2.1.2 Kukersite distribution in Estonia and geological strata ............................... 13 2.1.3 Characterization of Estonia deposit ............................................................. 14 2.1.4. Narva mining field backround information and location description ......... 16 2.1.5. Narva oil shale quarry geology ................................................................... 18 2.3 Geotechnical model ............................................................................................ 21 2.3.1 Description of soils and rocks ...................................................................... 22 2.3.2 Description of discontinuities ...................................................................... 23 2.3.3 General geomechanical properties of rock .................................................. 24 2.3.4 Geomechanical properties of rock – Hoek & Brown parameters ................ 27 2.3.5 Model parameters – rock mass properties ................................................... 29 2.3.6 General model description ........................................................................... 31 2.3.7 Hydrogeological description ........................................................................ 34 2.3.8 Model description for the highwall – RS2 ................................................... 36 2.3.9 Model description for the highwall – FLAC ............................................... 38 2.4 Technology of (punch) longwall mining ............................................................ 40 2.5 Chain pillar design .............................................................................................. 44 2.5.1 Empirical method ......................................................................................... 45 4. Results ................................................................................................................ 48 4.1 Numerical modelling results for the highwall slope stability ............................. 48 4.2 Results from ALPS (Chain pillar stability) ........................................................ 59 5. Discussions and recommendations ..................................................................... 67 5.1 Higwall slope stability analysis .......................................................................... 67 5.2 Chain pillar stability analysis .............................................................................. 69 References ..................................................................................................................... 71 Appendices ................................................................................................................... 74 Appendix 1. Geological crossection of Northern-Kiviõli oil shale quarry [36] ....... 74 Appendix 2. Production layer thickness along Estonia deposit [11] ........................ 75 Appendix 3. Borehole data (see Figure 3) [18] ........................................................ 76 Appendix 4. Production layer physical parameters [37] .......................................... 77 Appendix 5. Safety factor for a 3-entry system ........................................................ 78 Appendix 6. Safety factor for a 2-entry system ........................................................ 79 Appendix 7. Safety factor related to length of the pillar (undersized width) ........... 80 3 4 ABSTRACT STABILITY ANALYSIS OF A LONGWALL MINING IN NARVA OIL SHALE MINE Taavi Lõhmuste, Ott Oisalu Civil Engineering Luleå University of Technology Year 2017 Oil shale industry in Estonia is looking at other mining technologies as alternative to strip mining and room and pillar mining methods. One such alternative to the room and pillar method is the punch-longwall mining method. Enefit Kaevandused AS, one of the major oil shale companies in Estonia, plans to employ this technology in exploiting some of its resources in the near future. This thesis examines the different stability problems related to the planned punch-longwall mining project in Narva oil shale mine. Determining optimal chain pillar dimensions and stability of the punch-longwall highwall slope are the main objectives of this project. Rock mechanical analyses have been done and recommendations are made based on the rock mechanical aspect of the mining process. Taavi Lõhmuste is responsible for the chain pillar stability analysis and Ott Oisalu for the punch-longwall highwall slope stability analysis. It is essential to understand the geology of a certain area in order to make accurate stability assessments. Because of the previously stated requirements, the geology of Estonian oil shale deposit is examined in the first part of the thesis in order to determine the geological and rock mechanical conditions to set the foundation for further analyses. In conclusion, for the part of the highwall slope, a properly designed barrier pillar plays a key role in the stability of the slope. After reviewing and analyzing the results of both highwall slope numerical models, it can be stated that the minimum length for the barrier pillar that still will yield in stable highwall slope is 65 meters. For the part of the chain pillars, in conclusion, it can be determined that optimal chain pillar dimensions that should be suitable, from the stability standpoint, are 6x6 meters for 3-entry system and 7x7 meters for 2-entry system (length x width). Keywords: longwall mining, oil shale, stability analysis, chain pillars, barrier pillar, slope stability 5 6 ACKNOWLEDGEMENT We would first like to thank our thesis advisor Dr David Saiang of the Department of Civil, Environmental and Natural Resources Engineering at Luleå University of Technology. We would also like to acknowledge Dr Oleg Nikitin at Enefit Kaevandused AS as the second reader of this thesis, and we are grateful for his very valuable comments on this thesis. Finally, authors of this thesis would like to acknowledge Enefit Kaevandused AS for their part in making this project come to fruition. 7 1. INTRODUCTION Oil shale is the most important energy resource of Estonia and related industries are biggest job providers in the country. There are three big energy companies involved in the oil shale mining and processing industry: Eesti Energia AS, Viru Keemia Grupp AS and Kiviõli Keemiatööstus OÜ. These companies employ about 9500 people and the whole sector contribute about 4% of the national cross domestic product [1] [2]. This Master’s degree project is done in cooperation with the Enefit Kaevandused AS. 1.1 Background The bedding depth of the commercial oil shale bed is increasing southwards in the Estonia deposit. In Estonian practice, the economically reasonable depth of oil shale bed for opencast mining is up to 30 m. For greater depths than this, underground mining methods are employed. The mining front in Narva quarry is approaching this limit, i.e., the thickness of overburden is reaching 30 m. Also, in the SW part of the quarry the oil shale reserves are covered with peat reserves, and there underground mining might be the only way to extract the oil shale resource without destroying the upper peat layers. Enefit Kaevandused AS is planning to test underground mining (longwall mining) method as a potential technology for oil shale extraction for greater depths. Longwall mining technology has become significant in connection with the Enefit Kaevandused AS plan to deploy the technology (longwall mining) in the southern part of the Narva quarry mining field. In the first decade of the 21st century, Viru Keemia Grupp at the time considered to introduce longwall mining in the yet to be developed Ojamaa mine, but most likely due to the outbreak of the global economic crisis in 2008, it was decided to go with a safer version, with the already well-known room-and-pillar mining technology [3]. Longwall mining could be considered for implementation at the prospective Uus-Kiviõli