外文翻译---土压力理论在薄煤层回填支柱设计中的应用.docx

翻译部分英文原文design of backfilled thin-seam coal pillars using earth pressure theory1. 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. however, 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. 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 into 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 openings 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 surrounding 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 fairly 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 (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 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 behavior 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-seam 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 the 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 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 left 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 (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 mechanism 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 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 support (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 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 deformation 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 passive 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 in 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, 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 functionality 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-advancing 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 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. cohesion 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 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 support 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 additional 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 for 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 decreaseand 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 determined using earth pressure theory, can readily be incorporated into standard pillar design. typical pillar design is based on ultimate strength, which asserts that a pillar will fail when the load on the pillar exceeds the pillars strength. since a confining pressure acts to increase a pillars strength, a relationship between the original pillar strength, confining pressure, and increased strength is necessary to incorporate earth pressure theory into standard pillar design. such a relationship exists and is based on mohrs failure criterion. therefore, design of backfilled pillars can be performed following a common procedure that now also allows for variables such as backfill density, cohesion, and friction angle.中文译文 土压力理论在薄煤层回填支柱设计中的应用 1导言设计出的sam技术已经能从小于90厘米厚的煤层中提取煤炭。在理论上，这种技术能提取的全部高度的煤层，同时能尽量减少废石，并利用遥控操作，使能采煤机推进到一百八十米（六百英尺）的煤层中去。然而，煤层太薄以至于采煤的回收率相当低，并且煤的开采会随着煤层深度的增加而迅速的减少。为了增加薄煤层矿井的回收率，在保证支柱的设计安全下，必须使支护尺寸尽可能的小。回填在可以增加煤的开采量的同时也提供必要的支护来，从而保持了地下开采运作的完整性。地下回填已经在煤矿的开采和回填（托马斯，1979年）中得到了应用。回填材料被应用到地下提供不在为开采提供工作平台和有限的支护，从而减少了其中有可能被大规模移动和支护坍塌而填补了的露天场地空间,（巴瑞特等人，1978年）。回填阻止了由于煤炭开采而留下的空间的坍塌（艾吉森等人，1973年）。因此，在地下的开放空间安置支护往往可以防止剥落的围岩进入到采空的区间，所以要增加支护的有效强度和承载能力。这种类型的支护机制不仅提供支柱和墙壁，还防止了顶煤和顶板下落，并尽量的减少了地表沉陷、提高支护的回弹能力（科特斯,1981年）。虽然回填的支护能力是人所共知的，但它仍然难以量化。广旭和茂元等人已经提出了回填支护判断的模型和方程（蔡，1983年；广旭和茂元，1983年）, 已经使用模拟实验室对支柱-回填系统进行了设置,这是用来研究支护支撑与实际支护模型之间的关系。但是在一般情况下，这些模型和实验的检测,都依赖于本地的经验以及回填支护、材料性能和几何特性之间的关系。因为sam技术仍然是在一个发展的阶段,所以需要一个简单而可靠的估算方法来评价回填支护的等级,这种方法是基于现有的知识之上的。有建议说古典土压力理论可以用来估算作用于支护上的侧向土压力。支护对周围支柱和拱顶的变形预期的效果已经分析出来了。支护的作用已经纳入到了支柱设计中，因次新的支柱的宽度可以得到计算，同时煤的回收产量也可以确定了。2稀薄煤矿使用sam技术，稀薄煤层被称作为地下露天矿的未开采工作面。图1描述了由于煤层运输和削减而形成的几何平面层。这种支护系统是由于煤层开采而留下的。使用sam技术在大约60度的角切开和剪切是可能的，这样可以减少采矿设备的转动半径，同时这又不会影响柱子尺寸的设计。 每个采区的长度是1200米（1000ft）。每个采区的宽度随深度变化而变化，这是为了能够容纳通过每个采区中心的分隔柱子支护。然而，采区的宽度将至少大于两倍的sam进程所需的距离，在这种情况下至少需要300米(1000ft)。 在采区开采的过程中，还有分隔柱和一系列的支护体系留了下来。 在采区开采结束后，大量的分隔柱子也被留了下来从而维护了巷道两边的安全。 图2是一个煤层开采的断面图。这种形式使我们可以同地下露天矿未开采工作面做个比较；煤层通过采区的中心部位，以及每一次开采上方和下方都留下了余煤。开采宽度是3米(10ft)，并且裁减高度与煤层高度是等效的(少于90厘米(36in)。在无效采空区，sam每一次开采和支护的退出，要么使用液压，要么使用气动。3土压力理论的应用 前面部分所讲的应用土力学来量化回填支护体系的思想并不是前所未有的理论。而应用土压力理论来解释支护行为的机理是被广泛接受的。不过，在地下煤矿中，一般认为应用土压力的理论和观念不足以量化支护的等级。由于对于荷载从围岩向支护摩擦影响转移认识的程度有限，因此使得土压力理论在回填支护中的使用变得困难（托马斯，1979年）。在薄煤层矿井中，由于支柱设计的失败，使得sam的应用变得困难，