采煤专业外文翻译土压力理论在薄煤层回填支柱设计中的应用Word文件下载.docx

1、1. IntroductionThe Self-Advancing Miner has been designed to extract coal from seams less than 90 centimeters thick. The SAM allows for extraction of the full seam height while minimizing waste rock, and utilizes remote operation that allows the miner to advance up to 180m （600ft） into the seam. How

2、ever, the coal seams are so thin that the recovery rates of this mining method will be fairly low and will decrease rapidly with the depth of mining. In order to increase the recovery from thin-seam mines, pillars must be designed as small as possible without compromising the stability of the mine.

3、Backfill can provide the support necessary to maintain the integrity of the underground workings while allowing for increased extraction. The placing of backfill underground has predominantly been a practice employed in cut-and-fill mines （Thomas, 1979）. Backfill material is introduced underground i

4、nto previously mined stopes to provide a working platform and localized support, reducing the volume of open space which could potentially be filled by a collapse of the surrounding pillars （Barret et al., 1978）. The presence of fill in an opening prevents large-scale movements and collapse of openi

5、ngs merely by occupying voids left by mining （Aitchison et al.1973）.Therefore, the placement of fill in open spacesunderground tends to prevent the unraveling/spalling of the surrounding rock mass into the mined-out space, effectively increasing the strength, or load bearing capacity, of the surroun

6、ding rock mass. This type of support mechanism not only helps provide support to pillars and walls, but also helps to prevent caving and roof falls, minimize surface subsidence, and enhance pillar recovery （Coates, 1981）. Although the support capability of backfill is well known it still remains fai

7、rly difficult to quantify. Models and equations for the determination of backfill support have been proposed （Cai, 1983; Guang-Xu and Mao-Yuan, 1983） and pillar-backfill systems have been modeled using laboratory set-ups in order to correlate the actual support behavior of fill with proposed models

8、（Yamaguchi and Yamatomi, 1989; Blight and Clarke, 1983; Swan and Board, 1989; Aitchison et al., 1973）. But in general these models and lab tests are dependent on local experience and empirically derived relationships between backfill support, material properties, and mine geometry. Since the SAM is

9、still in development there is a need for a simple and reliable method of estimating the magnitude of support provided by backfill based on existing knowledge. It is proposed that classical earth pressure theory can be used to estimate the lateral earth pressure applied by backfill. The anticipated b

10、ehavior and response of fill to deformations of the surrounding pillars and roof are analyzed here. The supporting effect of backfill is incorporated into the original pillar design （unsupported） so that new pillar widths can be calculated and the increase in recovery can be determined.2. The thin-s

11、eam coal mineA thin-seam coal mine, employing the SAM technology, can be thought of as anunderground highwall mine. Figure 1 depicts the simplified panel geometry created by the development of entries and cross-cuts, and the system of pillars left behind after panel extraction. It is probable that t

12、he cuts and cross-cuts will be angled at approximately 60 so as to decrease the turning radius of mining equipment, but this will not effect pillar design. The length of each panel is 1200m （4000ft）. The width of each panel varies with depth in order to accommodate a barrier pillar that runs through

13、 the center of each panel. However, the panel width will be at least Greater than twice the distance required for one SAM cut,in this case 300m（1000ft）.Upon extraction of the panels, the barrier pillar and a series of pillars left between cuts remain in every panel. Large barrier pillars are also le

14、ft at the ends of the panels to protect the cross-cuts. Figure 2 is a cross-sectional view of the cutting face. The face evokes the highwall mine comparison; the coal seam runs through the middle of the panel and a portion of the panel material is left above and below each cut. The cut width is 3m （

15、10ft） and the cut height is equivalent to the seam height （less than 90cm （36in）. It is intended that as the SAM retreats from each cut, backfill will be either hydraulically or pneumatically placed in the mined-out void.3. Application of earth pressure theoryThe idea that the backfill support mecha

16、nism described in the previous section can be quantified using principles taken from soil mechanics is not new. A broad understanding of fill behavior has always been dependent on knowledge of earth pressures. However, earth pressure theories and concepts have not generally been considered adequate

17、in properly quantifying the magnitude of fill support in underground mines. Limited understanding about the transfer of loads from the surrounding rock to the fill and frictional effects, along with mine geometry, have made it difficult to apply the concepts of earth pressure theory to backfill supp

18、ort （Thomas, 1979）. What makes the case of the SAM operating in a thin-seam coal mine different is the concept of designed failure of the pillars so that deformations capable of mobilizing the passive resistance of the backfill will occur. From civil engineering design of retaining walls it has been

19、 shown that the movement required to reach maximum passive earth pressure within in a loose sandy soil is 4% of the wall height （Clough and Duncan, 1971）. The denser the soil, the less movement required. Applying this guideline to the thin-seam coal mine; for a pillar height of 90cm lateral deformat

20、ion of the pillar must be at least 3.6cm for a loose, sandy backfill to reach maximum passive earth pressure conditions. The initial stages of pillar failure may not produce movements that large, but over time creep deformation will almost certainly produce movements large enough to initiate full pa

21、ssive restraint within the backfill.Vertical loading of the back fill by the immediate fractured roof strata can easily be incorporated into earth pressure theory. The weight of the caved material lying on the fill is equivalent to a surcharge load. Over time, bulking of the caved material results i

22、n a vertical load equal to the overburden pressure. Friction between the pillar and fill will have an important effect on the magnitude of the passive pressure applied by the fill. It is expected that the friction between a spalling coal pillar and granular fill material will be quite high. However,

23、 frictional effects can be accounted for in earth pressure theory. 4 Usefulness of backfilled pillar design using earth pressure theoryThe incorporation of Rankines method or Log-spiral analysis into standard pillar design has its limitations. In terms of civil engineering applications the functiona

24、lity Of each of those methods has been verified through experience and each is used in the design of structures. Since no precedent exists for earth pressure theory being applied to the design of backfilled pillars the usefulness of the approach cannot be corroborated. Furthermore, the Self-Advancin

25、g Miner technology is not currently in use nor are any thin coal seams being extracted in a similar manner. The purpose of devising a method of backfilled pillar design using earth pressure theory is to see what conditions may be necessary for backfilling to be practical or economical. Figure 7 is a

26、 plot of recovery rate versus mining depth based on the panel dimensions and pillar widths of Figure 6. This type of plot can be developed for any set of the following conditions:1. Post-peak strength of the coal pillar2. Friction angle of coal3. Backfill density4. Friction angle of backfill5. Cohes

27、ion of backfill6. Magnitude of roof loading7. Mining dimensions （cut width, length, and seam height）.Thus the importance of any variable can be determined in terms of stability and overall recovery, and a concept of what type of backfill may be necessary to achieve a certain rate of recovery can be

28、formulated. In turn, a more detailed economic analysis can be carried out in terms of the cost of backfilling required to produce an additional ton of coal （Hume and Searle, 1998; Donovan, 1997; Donovan and Karfakis, 2001）.5 ConclusionThere is little doubt that backfill has the ability to provide su

29、pport to surroundingpillars. However, quantifying the magnitude of that support has proven to be quite difficult. Earth pressure theory, commonly used in the design of civil engineering structures, may provide a preliminary toolfor estimating the amount of support that backfill can provide. The addi

30、tional strength that backfill provides to surrounding pillars is imparted as a horizontal pressure along the sides of the pillars. This behavior of the fill in response to lateral deformation of the pillars is similar to that of earth-retaining structures. Rankines method and the log-spiral method f

31、or determining passive earth pressure coefficients can be used to determine the magnitude of fill support. The extent of roof caving, and subsequent surcharge loading of the backfill, is the most important factor in terms of the magnitude of lateral support provided by the backfill. pillar sizes dec

32、reaseand recovery increases. However, the fracturing of the immediate roof, and its time-dependency, is reliant upon local geologic and mining conditions. Thus it is difficult to predict and quantify the extent of roof caving. The proposed method of backfilled pillar design based on earth pressure theory will remain limited until a more rigorous method for assur-ing roof caving, and determining the magnitude of vertical loading, is developed. The passive resistance provided by the backfill, and determ