澳大利亚地下开采方法的地质和岩土工程方面概述外文文献翻译、中英文翻译

英文原文Geological and geotechnical aspects of undergroundcoal mining methods within AustraliaB. Scott P. G. Ranjtih S. K. Choi Manoj KhandelwalAbstract : About one quarter of the coal produced in Australia is by underground mining methods. The most commonly used underground coal mining methods in Australia are longwall, and room and pillar. This paper provides a detailed review of the two methods, including their advantages and disadvantages, the major geotechnical and operational issues, and the factors that need to be considered regarding their choice, including the varying geological and geotechnical conditions suited to a particular method. Factors and issues such as capital cost, productivity, recovery, versatility and mine safety associated with the two methods are discussed and compared. The major advantages of the longwall mining method include its suitability for mining at greater depth, higher recovery, and higher production rate compared to room and pillar. The main disadvantages of the room and pillar method are the higher risks of roof and pillar collapse, higher capital costs incurred as well as lower recovery rate.Keywords : Longwall Room and pillar Geological GeotechnicalIntroduction :Mining in Australia is a significant primary industry and contributor to the economy of Australia and encouraged immigration to Australia. Many different ores and minerals are mined throughout the country. With the increase in coal demand and growing awareness towards sustainable development, the coal industry has drawn a consensus over the need for increased production from underground coalmines. Around the world, the majority of coal reserves are recoverable using underground mining techniques. At the moment, almost two-thirds of coal production comes from underground mines, however, in Australia this statistic is significantly lower (ACA 2006). Currently in Australia, the majority of underground coal mines are located in New South Wales and Central and Western Queensland, where thinner black coal seams suit the underground mining methods.There are a number of different types of access modes for underground mining. These include drift, incline/ decline and shaft, and can be used in conjunction with either of the three modes for underground mining within Australia. Drift is generally used when the coal deposit is inside of a hill, and mining is undertaken by entering directly into the hill (Ghose 1984). Incline/decline is created at the ground level of a valley, where an adit is constructed and slopes down to the coal. Shaft is used with an elevator, which stretches from the surface to the coal seam underground (Wilson 1983).The main aim of the paper is to identify and compare various techniques used for coal extractions and the selection process of those techniques for a particular site based on geological, geotechnical and other factors. The two major methods of underground mining within Australia and around the world are room and pillar and longwall mining, and these two methods will be discussed in details below.Current states of Australian underground and open-cut coal mining operationsIn order to gain an understanding of the current state of coal mining operations in Australia, a broad overview is given before method suitability for coal mines is discussed.In Australia, open cut mining produces the most amount of coal for both export and internal uses. In 2004 for example, 81.5 million tonnes of coal was mined using underground methods, whilst 296.3 million tonnes were obtained using methods within an open cut system (University of Wollongong 2006). This is of no surprise as nearly two-thirds of all operating mines within Australia are open cut, as can be seen from Table 1 and Fig. 1 below.Table1 Type of mines operating within Australia (GNSW 2006;GSA 2006; GWA 2006; GT 2006; GV 2006; GQ 2006)Mine types by stateStateUndergroundSurfaceTotal coal minesQueensland103040New South Wales272552Western Australia066Tasmania123Victoria178South Australia011Total3971110Fig.1 Map of Australian coal basins (DPMC 2006)Within Australia, brown coal is typically found in the southern part, with black coal found in the basins of New South Wales and Queensland. Before proceeding further, a quick overview of coal rank and classification is given. Typically, coal rank is classified into three distinct categories depending on the degree of metamorphism that the coal forming material has endured as it matures from peat to anthracite. These are lignite, sub-bituminous and bituminous, and the properties of these greatly influence the type of method used to exploit the coal.As mentioned, surface mining or opencast mining is the predominant method used in Australia. Opencast mining on a large scale first commenced in Australia in the 1960s, where imported draglines were the main means of stripping overburden. This method continued to be used over the next 2030 years, and still today, however, as the seams became deeper and the complexity of the coal seam increased, other equipments such as truck and shovel, and dozers, were introduced (Westcott 2004).Today, draglines and truck and shovel operations, or a combination of the two, are the predominant modes of equipment used in opencast mines, as seen in Fig. 2 below.Fig.2 Opencast Coal Mining Equipment used in Australia (Westcott 2004)Selection of excavation methodThe decision on whether to operate an above or underground mine is heavily influenced by a couple of important factors. The major factor in deciding on whether to go underground or open cut is the stripping ratio (Whittles et al. 2007). This is defined as the ratio of the volume of overburden (BCM) moved to the amount of coal produced (tonnes). As a general rule, anything past 20:1 is considered too large a ratio for above ground coal mining as large amounts of overburden are required to be moved in order to expose the coal seam, thus underground methods should be considered. Another factor in deciding on the technique to be employed is the type of coal to be mined. If the coal deposit consists of lignite, which is Tertiary in age and ranges from about 15 to 50 million years old, then above ground methods should be more closely considered. This is due to the fact that lignite is a much softer material than black coal, which increases the possibility of roof collapse or material collapsing from above during mining due to the younger, unconsolidated and softer material overlaying the brown coal. Careful consideration, however, would also need to be given, when mining brown coal above ground, as a strong base for the large, heavy equipment would be required to avoid bench collapse or other failure. Large, heavy coal haulage trucks may also find it difficult to operate on the softer lignite, especially during wet weather events, where the weight of the equipment results in large amounts of time lost due to trucks becoming bogged, wheel spin, etc.Other factors to be considered, which will be expanded upon shortly include: Life of mine. For example, is it feasible to outlay large capital for a small coal deposit? Required productivity. Do you need a high production machine or is it more feasible to mine constantly at a slower rate? Amount of capital available.If there is any plant currently available within the company, and can it be utilised?In the following sections on longwall and room and pillar coal mining, the typical geological and mining conditions for the techniques to be utilised will be discussed, including variations of the techniques, as well as expected productivity and costs experienced within the industry. The following is applicable to each proposed method (opencast or underground): No two mines are exactly the same. Geological profiles, weather, capital available, production, productivity requirements, recoverable reserves, etc. are all independent variables between different mines, and as such, it is impossible to prepare a standard document, which caters for every possible mine (Bise 1995). Large amounts of time are required by experienced engineers or specialist consultants during the preliminary and planning stages in order to design a mining method suited to a particular location. Geotechnical issues are independent at each location, and a detailed investigation at the very least should be undertaken in order to understand the groundconditions, geological profile, etc. (Wilson 1983). The geotechnical issues outlined within this paper include different modes of failure, soil properties, etc. however, it is not within the scope of this paper to detail every possible geotechnical issue with regards to coal mines. Major problems will be identified along with the conditions that cause such circumstances to occur. Costing of mine equipment and productivity is of a broad nature, and can be calculated using the following formula proposed by Noaks and Landz 1993. The cost in 1992 $A has been adjusted to 2006 value using the recommended formula:Cost Now = (Cost Then)(Cost Index Now)/(Cost Index Then)where, the cost price indexes (CPIs) for both 1992 (CPI, March 1992: 107.1, open cut; 108.1, underground) and 2006 (CPI, June 2006: 167.0, open cut; 152.0, underground) have been obtained from the Australian Bureau of Statistics (ABS 2006). All values and productivity are generated as a preliminary estimate for a pre-feasibility study level of accuracy (25%), and does not replace an engineered cost estimate or feasibility study. The accuracy of any estimate will be directly proportional to the quality and quantity of data available and to the time and effort put into its preparation and proper execution (Noaks and Landz 1993).The following sections outline the two underground coal mining alternatives (longwall, and room and pillar mining) specifying which geological conditions are better suited to each method, as well as geotechnical issues involved.Longwall miningLongwall mining is the most common of the underground coal mining methods used in Australia. It suits sites where coal seams are thicker, wide and have a consistent coal profile with gentle dip. In longwall mining, large rectangular sections of coal are identified and removed in one continuous operation (Trueman et al. 2009). Basically, a panel, or block, of coal is created by driving a set of headings into the section of coal (panel) for a certain distance (typically 1.53 km long). These sets of headings are generally spaced at a distance of approximately 100250 m (330820 ft) apart, and are joined together to allow the longwall mining machine to work along the longwall face. The mechanised shearer runs along the face, cutting and removing the coal as the mine advances along the length of the headings.As the coal is being cut and dropped onto a chain conveyor, temporary hydraulic-powered roof supports automatically follow the direction of the shearer to hold up the roof while the coal is being extracted. These supports provide a safe working environment, and as the mine advances, so do the support jacks, and the roof area behind the face is allowed to safely collapse, forming an area known as the goaf. In the main roadways within the mine, for use by mine personnel, transportation of maintenance equipment, etc. roof bolts are placed in the ceiling to avoid collapse. Once the shearer has completed extracting the coal from the panel, it is moved to a new location, and repeats the process.This method of mining is more efficient than the room and pillar method, with recovery rates averaging approximately 75%. However, the equipment is more expensive and cannot be used in all ground conditions. These issues, among others, will be discussed further below.As mentioned at the beginning of this section, longwall mining is the predominant underground method of extracting coal within Australia, with approximately 70% of underground coal mines utilising the technique, all of which are in either New South Wales or Queensland. The method accounts for 89% of Australias total underground coal production (University of Wollongong 2006). It is a relatively recent introduction in Australia, with the first longwall mine being developed in 1963, however, there are currently 27 in operation including the Beltana, Metropolitan and Newstan coal mines in New South Wales, and the Crinium, Kestrel, Oaky North and Newlands Southern mines within Queensland.Kelly (1999) identified the fact that shear failure, rather than tensile, is the major failure mechanism in a number of Australian longwall mines monitored by the CSIRO since 1994. The failure has occurred further ahead of the retreating face than traditional geo-mechanics theory predicts and is considerably affected by the geological conditions of the site. Other factors influencing failure include goafing mechanics of previous block and pore water pressure.Hebblewhite (2003) introduced the concept of core geotechnical risks associated with longwall mining, that is: any risk associated with a major hazard or potential hazard that is an inherent feature of a generic mining method. Almost by definition, core risks cannot be totally eliminated, and must therefore be controlled and managed during the life of the mining method or system of work. The paper identified some major core geotechnical risks associated with longwall mining, and can be seen in Table 2.Table2 Core geotechnical risks associated with longwall miningHazardConsequenceSurface subsidenceDisturbance/damage to surface features (natural and man-made), and to sub-surface, such as aquifers.Face instability/periodic weightingLoss of face/roof control; production disruption; equipment damage; operator safety threatenedCaving hang upWindblasts (range of consequent safety implications); excessive pillar and face loading; unpredictable subsidenceStructural geology disruption to panel blocksProduction disruption and potential sterilisation of reserves leading to major economic impact; adverse face ground conditionsAbutment stresses on developmentAdverse conditions/potential failure in gate roads and chain pillarsRisks identified within Table 2 such as surface subsidence are inevitable and will occur on almost all longwall mine sites, and must be managed effectively, whilst others such as caving hang up causing air/wind blasts are avoidable if appropriate planning is undertaken and precautions followed.Certainly, the geotechnical suitability, issues and risks mentioned herein are not in any way the sole elements to consider when planning, developing or operating longwall mines. It is simply an identification and description of major factors involved within the longwall mining process. Other issues and business considerations following, relevant to specific sites, should also be taken into account when considering coal mining methods.Other issues and considerationsThe previous section describes geotechnical considerations relevant to longwall mining. The following section will consider other issues which may arise during longwall operations including safety, production, productivity, equipment size, make, etc. and options for mine layout. As each site is independent of another, it is difficult to recommend certain templates for selecting the mining method, however, it is the aim of this section to discuss what options are available and under what conditions they are best suited for, as well as common issues arising during the application of a particular method.The importance of productivity in all mining cannot be overlooked, and the main increases over the years have generally come from advancements in technology. One of the key factors over the past 20 years in making longwall productivity gains has been the evolution of larger longwall panels, made possible by technology advancements, upwards of 3,350 m in length by 320 m wide as opposed to typical lengths and widths in the mid-1980s of 1,525 and 180 m, respectively (Kvitkovich and Weisdack 2005).It is expected that longwall technology will continue to improve for a number of years, thus providing greater options for longwall unit selection, which ultimately has a great influence on productivity (Peng and Chiang 1984). In1992 for instance, longwall equipment was very diverse in size and capacity, as it still is today, with shearer power ranging from 150 to 1,080 kW, and face conveyor capacity running between 940 and 2,600 tonnes/h. These statistics demonstrate the various options available when purchasing longwall equipment, which will ultimately have a large influence on the costs and expected productivity of a project.Tasman Asia Pacific (Anon 1998) conducted an analysis on longwall mining in 1998 by comparing best practice performing longwall mines in the USA with a number of longwall mines operating within Australia. This analysis concluded that the average productivity of the Australian mines was approximately 25% less than that of the USA mines. The analysis was limited to the core mining operations of longwalls (shearing, roof support, transportation of the coal, labour and maintenance) and therefore, because the operating characteristics of the mines were fairly similar, estimated productivity gaps likely indicated differences in management and work practices. The results from this report indicate areas which typically affect productivity in longwall mines.The report identified the major differences between the Australian and USA longwall mines as: higher non-production times during shift changeover within Australian longwall mines, lower utilisation of shearers within Australian longwall mines, and geological differences.These results indicate key areas which, if focused upon and managed appropriately, can influence productivity level