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英文原文Mining subsidence control by solid backfilling under buildings ZHA Jian-feng1, 2, 3, GUO Guang-li1, 2, FENG Wen-kai3, WANG Qiang1, 2 1. Key Laboratory for Land Environment and Disaster Monitoring of the State Bureau of Surveying and Mapping, China University of Mining and Technology, Xuzhou 221116, China; 2. Jiangsu Key Laboratory of Resources and Environmental Information Engineering, China University of Mining and Technology, Xuzhou 221116, China; 3. State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China Received 19 June 2011; accepted 10 November 2011 Abstract: Solid backfilling mining can reduce the buildings damage caused by mining greatly.The reduction of subsidence value, the slow advancing speed and the subsidence caused by backfilling body compaction are the main reasons that solid backfilling mining velocity decreases significantly. Based on the research of mechanism, some principles on subsidence control of solid backfilling mining under buildings were proposed. The equivalent mining height was designed according to the fortification criteria of buildings and their attachment structures, which enables the ground movement and deformation caused by mining to be less than the corresponding fortification criteria. Key words: solid backfilling mining; subsidence control; mining under buildings 1 Introduction Coal resources exploitation leads to a series of environmental problems, such as solid waste pollution, farmland reduction, and buildings damage. Meanwhile, plenty of coals under buildings, water and railways are not exploited in China. According to the data from China Coal Ministry, coal under buildings accounts for 63.5% of the total buried 13.79 billion tons coal 1. Conventional mining technologies (caving method, strip mining, etc) usually cause contradiction between coal mine and local residents in addition to loss of resources. Solid backfilling mining is the technology which uses equipment to fill gangue, coal ashes and other solid waste into goaf to occupy the space caused by coal exploitation. Therefore, the roof and floor movement space decrease, and the surface subsidence decreases. Meanwhile, during the process of filling, large numbers of gangue, coal ashes and other solid wastes are consumed. So, we can call the solid backfilling mining a green technology which integrates subsidence control with environment protection. Now, environment pollution and mining under buildings, water and railways are big problem in China. More coal mines pay attentions to solid backfilling method due to its successful industry experiments. Recently, several coal mines, such as Xingtai 2, Jining No.3 3, Zhaizhen 4 have successfully applied this new method. Based on the analysis on subsidence control mechanism of solid backfilling mining, principles of solid backfilling mining design are given in this work. Moreover, for the aim of subsidence control, design methods of solid backfilling mining are also proposed. 2Subsidence control mechanism 2.1 Solid backfilling mining technology Solid backfilling mining technology contains three classes: fully mechanized solid backfilling mining technology, conventional mechanized solid backfilling mining technology and roadway excavation solid backfilling mining technology. Among them, fully mechanized solid backfilling mining, whose working face layout mode is similar to fully mechanized mining, is the most widely used one. In the case of solid backfilling technology, the filling working face is deployed on one side of the goaf (i.e., at the back of mining working face), and a transportation belt, which shifts the solid material to scraper chain conveyor, is set in the headentry of working face. Two scraper chain conveyors with the same direction are set at the front and rear of hydraulic support. The rear of hydraulic one is called solid backfilling conveyor, which hangs under the horizontal rear canopy and several dropping holes are made on it. Solid backfilling conveyor is connected with the transportation belt, then solid materials can be transported to solid backfilling conveyor and fall from dropping holes, until the goaf is full of solid filling material. All the backfilling tasks can be done at the shield of horizontal tail beam (Fig. 1). As shown in Fig. 1, solid filling materials fall into goaf through dropping holes on solid backfilling conveyor, and then they are compacted by the push-tamp equipment which is set at the rear of hydraulic support, finally the density and ratio of backfilling body can be increased. 2.2 Subsidence reduction mechanism From the description of solid backfilling mining technology, the goaf is occupied by compacted solid material. The common solid backfilling materials (gangue, coal ashes, loess) are discrete medium. While the ground pressure is added, backfilling materials will be compacted, broken and the particle gradation can be improved, which can enhance the anti-compact capability significantly. Figure 2 shows the stressstrain curve of the gangue compression in the cylinder compression test. When the subsidence increases, the reaction of overburden strata suffered from backfilling body raises until it is balanced with the overburden stratas pressure, and then strata movement stops. A lot of similar materials and numerical simulation result show that 67 the overburden strata usually develops fracturing zones and bending zones when the solid backfilling technology is used, and the overlying strata subsides heterogeneously. Therefore, in the critical mining conditions, the surface subsidence value of solid backfilling mining depends mainly on the subsidence of roof which is determined by mining height and final compression value of the backfilling body. Compared with the caving method, the roof subsidence space, which is the difference between the mining height and the final compression height of backfilling material, decreases significantly. This is the main reason why solid backfilling mining can reduce subsidence. 2.3 Slow down subsidence velocity mechanism In fact, strata movement of solid backfilling mining is a process that overburden strata moves towards goaf and compacts the filling body, then the filling body is consolidated and the anti-compression ability of it increases until the reaction is balanced with the press of overburden strata. After coal exploitation, the ground pressure at the top of coal seam diverts to the wings, and at this time, the filling body is unloaded. While the working face is advancing, the stress on the filling body will recover to the original rock stress, with the filling body compressed to “release” subsidence space correspondently.The subsidence space of roof decreases and it derives from the “release” space of backfilling bodys compaction which is the big difference between solid backfilling mining and caving method. The subsidence velocity depends on the advancing speed of working face, the depth of mining, the maximum subsidence value, the inclined length of mine area, etc. The results show that subsidence velocity has a positive correlation with the advancing speed of working face, the mining height and the maximum subsidence value, while it has a negative correlation with the depth of mining 89. The subsidence of solid backfilling mining can reduce greatly. Meanwhile, the advancing speed of solid backfilling mining is slower than that by the caving method for its technological characteristics. Moreover, the subsidence space is caused by backfilling body compaction. These are the main causes that solid backfilling mining velocity decreases significantly. 3 Subsidence prediction method Through the analysis on subsidence control mechanism of solid backfilling mining, it can be concluded that subsidence reduces greatly because backfilling body occupies the mining space, which means that it decreases the mining height. Actually, the mining height of solid backfilling mining, which is called equivalent mining height, is the difference between the mining height and the height of backfilling body after long time compaction and rheology by overburden strata. Similar material simulation and in-situ measurements of solid backfilling mining show that the subsidence basin by solid backfilling mining is the same as caving method with equivalent mining height. So, the subsidence prediction of solid backfilling mining can be switched to the subsidence prediction by caving method with equivalent mining height. The subsidence prediction parameters and methods of thin coal seams could be used for it. In the subsidence prediction of solid backfilling method, how to determine the equivalent mining height is the key issue. The analysis of subsidence influence factors by solid backfilling mining shows that the elements affecting the equivalent height are: the thickness of coal seam, the movement of roof and floor before filling, the backfilling rate, the prime compression of the backfilling body, the residual compression of the backfilling body, etc. Then the calculation of equivalent height can be divided in two parts: 1) The height of filling body (H0) filled into the goaf can be calculated with the following formula: H0=H (1) where is the gap between the backfilling body and roof, is the movement of roof and floor before filling, and H is the thickness of coal seam. 2) Equivalent height can be decided by the following formula: Hz=HH0+H0 (2) where is the residual compression rate of solid filling body. After that, solid backfilling mining subsidence can be calculated by the equivalent mining height and strata movement parameters in the coal mines. 4 Subsidence control principles and design methods under buildings 4.1 Subsidence control principles It can be known from the theoretical analysis of equivalent mining height that the key for subsidence reduction by solid backfilling mining is to reduce the mining height of coals. While under a particular geological and mining condition, the strata movement and deformation values can be decided by the equivalent mining height. The task of subsidence control of solid backfilling mining is that the surface movement caused by mining should be less than the fortification criteria of buildings. Thus, subsidence control principles of solid backfilling mining can be described as follows. The equivalent mining height is designed according to the fortification criteria of buildings and their attachment structures, which enables the ground movement and deformation caused by mining to be less than the corresponding fortification criteria. Based on the experience of mining under buildings, subsidence and horizontal deformation are usually selected as the fortification criteria of buildings in coal mines: WzWc zc where Wz is the maximum subsidence in the building area after mining with the designed working face; Wc is the fortification criterion of ground subsidence value in designed building area; z is the maximum horizontal deformation in the building area after mining with the designed working face; c is the fortification criterion of horizontal deformation value in designed building area. According to the former analysis, it can be concluded that in a certain working face, the ground subsidence and horizontal deformation are decided by the equivalent height solely, thus the former principles of subsidence control can be illustrated briefly as: HzHc where Hz is the designed equivalent mining height of working face; Hc is the critical equivalent mining height calculated by fortification criteria of buildings and their attachment structures. 4.2 Subsidence control design methods of mining under buildings The key part in the application of subsidence control principles by solid backfilling mining is to decide the designed and critical equivalent mining heights. The designed equivalent mining height can be calculated according to Eq. (2). Besides, the critical equivalent mining height can be got by the ground movement and deformation fortification criteria of buildings and their attachment structures. The flowchart is shown in Fig. 3. In the process of critical mining height computation, it is difficult to enable the prediction value of deformation to be the same with the fortification criteria. So, if the difference between the prediction value of deformation and the fortification criteria is less than 5%, it is acceptable. The prediction of buildings deformation is done with the probability integral method based on the equivalent mining height while the thin coal seam parameters are used in the process. When the working face is critical mining and the maximum deformation value locates in the buildings area, the schedule for calculation of critical equivalent mining height can be simplified. According to principles of probability integral method, the critical equivalent mining height can be expressed in the following formula, while the maximum subsidence in buildings area should be less than the subsidence criteria. While the maximum horizontal deformation in buildings area should be less than the horizontal deformation criteria. The critical equivalent mining height can be expressed as where q is the subsidence coefficient; H is the depth of mining; tan is the tangent of the main influenced angle; and is the incidence angle of coal seam. In practical, the smaller one of the two values, which are calculated by Eqs. (3) and (4) respectively, can be selected to ensure the safety use of buildings. 5 Engineering example 5.1 Geological and mining conditions of working face In this case, the working face is 450 m in length, 142 m in inclined width, 335 m in average depth, 8 in inclined angle and 3.3 m in thickness of coal seam. For the roof management, solid backfilling is adopted. The direct roof of working face mainly consists of siltstone- mudstone intercalation and post stone with the average thickness of 7.44 m. Sandy shale is the main part of the floor whose average thickness is 4.81 m. Villages, highways and other buildings locate above the working face and the land is flat. 5.2 Subsidence control design Above the working face, there are several buildings such as villages, the industry square of coal mine, some roads and the shaft. After researching the buildings qualities, and referencing to the 27th item of Regulations on Coal Pillar Design and Mining Regulations Under Buildings,Water, Railways 10, it is fixed that the fortification of subsidence in this district is 500 mm and the horizontal deformation criterion is 1.5 mm/m. The subsidence prediction parameters are inversed by the thin coal seam measurement, that are subsidence coefficient 0.73, horizontal movement coefficient 0.34, tangent of main influence angle 1.8, deviation of inflection point 0.1H. While the geological and mining conditions, and filling technology of this case are considered, the roof-to- floor convergence before backfilling is 100 mm and the gap between the backfilling body and roof is zero. The critical equivalent mining heights are calculated to be 0.69 m and 1.2 m by taking the subsidence and horizontal movement as the fortification standards respectively. According to the principles of subsidence control, the critical equivalent mining height of 0.69 m should be chosen. The residual compression rate should be less than 18.4% from Eq. (2), and the designed residual compression rate should be less than 15% for safety. Meanwhile, in order to master the strata movement laws of solid backfilling mining, and ensure the safety of buildings, strata movement monitoring stations have been set. 5.3 Subsidence control effect By using prediction technology of solid backfilling mining, the ground subsidence and horizontal deformation of solid backfilling mining and caving method are calculated respectively. The comparison between the predictions and the true measurements is listed in Table 1. From Table 1, it can be concluded that solid backfilling mining can reduce the buildings damages caused by mining to a large extent. At the same time, the true measurement values are far less than the results calculated based on the theory of equivalent mining height, which means that the result calculated by equivalent mining height is safety. 6 Conclusions 1) Solid backfilling mining can reduce the buildings damages caused by mining greatly. The decrease of overburden strata movement space, which is the difference between the mining height and the height of backfilling body after long time compaction and rheology by overburden strata, is the main reason that solid backfilling mining can reduce ground subsidence. 2) The reduction of subsidence value, the slow advancing speed and the subsidence caused by backfilling body compaction are the main reasons that solid backfilling mining velocity decreases significantly. 3) The fortification principles and technologies for solid backfilling mining under buildings are proposed. The equivalent mining height is designed according to the fortification criteria of buildings and their attachment structures, which enable the ground movement and deformation caused by mining to be less than the corresponding fortification criteria. In the process of designing, the critical mining height can be derived by subsidence prediction model according to the fortification criteria. 4) The case study shows that solid backfilling mining can reduce the buildings damage caused by mining to a large extent and the result calculated by equivalent mining height is safety. References 1 HE Guo-qing, LING Gen-di, YANG Lun. Mining subsidence M. Xuzhou: China University of Mining and Technology Press, 1991. (in Chinese) 2 ZHANG Xin-guo, ZHAO Yu-dong. Replace the gangue for coals, fulfill the green mining in Zhaizhen, coal mine J. Coal Processing and Utilization, 2008(1): 39. (in Chinese) 3 ZHANG Wen-hai, ZHANG Ji-xiong, ZHAO Ji-shen, WEI Shu-qun, JU Feng. Research on waste filling technology and its matching equipment in coal mining J. Journal of Mining and Safety Engineering, 2007, 24(1): 7983. (in Chinese) 4 WANG Guan-dong, DONG Feng-bao. Technology and application of high efficient mechanized backfill mining to fully mechanized longwall mining face in Zhaizhen Mine J. Coal Science and Technology, 2008, 36(1): 1516. (in Chinese) 5 MIAO Xie-xing, ZHANG Ji-xiong, GUO Guang-li. Method and technology of fully mechanized coal mining with solid waste filling M. Xuzhou: China University of Mining and Technology Press, 2010. (in Chinese) 6 ZHA Jian-feng. Study on the foundational problems of mining subsidence controlled in waste stow D. Xuzhou: China University of Mining and Technology, 2008. (in Chinese) 7 LIU Yuan-xu. Research on synergic relationship between waste filling mining surface subsidence control and cultivated land protection of plain mining area D. Xuzhou: China University of Mining and Technology, 2010. (in Chinese) 8 CUI Xi-min, CHEN Li-bin. Dynamic monitoring and mechanics analysis on large deformation of subsidence M. Beijing: China Coal Industry Press, 2004: 9. (in Chinese) 9 KANG Jian-rong, WANG Jin-zhuang, WEN Ze-min. Analysis of dynamic subsidence of mining overburden strata J. Journal of Taiyuan University of Technology, 2000, 31(4): 364366. (in Chinese) 10 National Ministry of Coal Industry. Coal pillar design and mining regulations under buildings, water, railways M. Beijing: China Coal Industry Press, 2005. (in Chinese) 中文译文建筑物下固体充填沉陷控制查建峰 郭广礼 冯文凯 王强1，土地环境与灾害监测国家重点实验室，中国矿业大学，徐州221116，中国2，资源环境信息工程江苏重点实验室，中国矿业大学，徐州221116，中国3，地质灾害防治地质环境保护国家重点实验室，成都理工大学，成都610059，中国摘要:固体充填采矿可以极大的减少由采矿造成的建筑物的破坏。减少沉降值，缓慢的推进速度和充填体压实是造成的固体充填采矿速度显着降低的主要原因。在机制研究的基础上，人们提出了一些建筑物下固体回填的开采沉陷控制的原则。等价采高是根据设防标准的建筑物及其附着的结构设计的，使开采造成的地表移动与变形是低于相应的设防标准。关键词：固体充填开采 建筑物下采煤 沉陷控制1引言 煤炭资源开采导致了一系列环境问题，如固体废物污染，耕地减少和建筑物损坏。同时，大量的建筑物下，水和铁路下的煤在中国没有被开采。根据来自中国煤炭部的数据，在建筑物下的煤占总的煤的储蓄量13.79亿吨煤的65.3%。传统的采矿技术（崩落法，露天采矿等）通常会导致煤矿和当地居民除了资源损失之外的矛盾。 固体充填采矿是一种使用设备用采空区的煤矸石，粉煤灰和其他固体废物填充采空区的技术。因此，屋顶和地板运动空间减少，地面沉降减小。同时，在填筑过程中，消耗大量的煤矸石，粉煤灰和其他固体废物。因此，我们可以称之为固体充填采矿沉降控制于一体的环保绿色技术。现在在中国，环境污染和建筑物下，水和铁路下采煤是个大问题。由于其成功的工业试验，更多煤矿重视固体回填的方法。最近，一些煤矿，如邢台，济宁三号，寨镇已经成功地应用这种新方法。在对沉降控制机制的固体充填开采分析的基础上，这个方法中给出了固体充填采矿设计的原则。此外，为了沉降控制的目的，也提出了固体充填采矿设计方法。2沉降控制机制2.1固体充填技术固体充填采矿技术包含三大类：完全机械化固体充填采矿技术，传统的机械化固体回填采矿技术和巷道掘进固体充填采矿技术。其中，完全机械化固体充填开采的工作面布局模式类似综采工作面，完全机械化固体充填开采是使用最广泛的一个技术。在固体充填技术的情况下，充填工作面采空区部署在一个面（即，在采煤工作面的背面），还有一个运输皮带，将固体物料的刮板输送机链条，设置工作面的头项。同一方向的两个刮板链式输送机安装在载液压支架在前方和后方。液压后部其中一个被称为固体回填输送带，挂在水平后冠层上而且还有一些滴孔在其上面。固体回填输送机和运输带是连接的，然后固体材料可以运到坚实回填输送和从下降洞下跌，直到采空区是全固体填充材料。全部回填任务，可以做到在水平尾翼梁盾（图1）。如图1所示，固体填充材料分为采空区通过下降固体回填输送带上的孔，然后他们推夯实设备在液压支架的后部，最后密度比和充填体可以增加。2.2减沉机理从固体充填采矿技术的描述，采空区被密实固体物质所占据。常见的固体回填材料（煤矸石，粉煤灰，黄土）是离散介质。当地面的压力增加时，回填材料被压实，破碎，然后颗粒级配可以得到改善，它可以反紧凑的能力显着增强。图2显示了煤矸石在汽缸内的压缩试验压缩应力应变曲线。当沉降反应增加时，从回填体遭受覆岩层的压力开始，直到它的上覆地层压力平衡，岩层移动，然后停止。 很多类似的材料和数值模拟结果表明6-7覆岩通常使固体回填产生压裂带和弯曲下沉带，使上覆地层不均匀沉降。因此，在关键的开采技术条件下，固体回填挖掘的地面沉降值主要取决于对顶板下沉，这是由挖掘，回填体的高度和最终压缩值确定。与崩落法相比，顶板下沉空间，这是采高和回填材料的最终压缩高度之间的差异，相比显着降低。这是可以减少固体充填采矿沉陷的主要原因。2.3减缓沉降速度机制 事实上，采矿覆岩地层运动对固体充填体压缩，然后充填体密实它的抗压能力增加，直到反应与覆岩达到一个新的平衡的一个过程。煤炭开采后，在煤层上方的地面压力转移到两翼，在这个时候，充填体卸载。当工作面推进，对充填体的应力将恢复到原岩应力，与充填体压缩沉降空间相应的“释放”。沉降空间顶板减小，它源于“释放”回填压实，这是固体充填采矿和崩落法之间相差很大的空间。沉降速率取决于工作面推进速度，深度挖掘，最大沉降值，矿区斜长等。结果表明，下沉速度与工作面推进速度，开采高度和最大沉降值呈正相关，当它与深度挖掘呈负相关的8-9。固体充填采矿塌陷可以大大降低。同时，因为其技术特点，固体充填采矿的推进速度是比崩落法慢。此外，沉降空间是由回填体压实造成的。这些都是固体充填采矿速度显着降低的主要原因。3沉降预测方法 通过对固体充填开采沉陷控制机制的分析，可以得出结论，沉降大大降低是因为回填体占据的挖掘空间，这意味着它降低了开采高度。其实，固体回填挖掘的高度，被称为等效采高，是挖掘高度和固体填埋高度在经过长时间受到上覆层压实和流变后的差异。通过充填开采相似材料模拟和现场测量，固体回填挖掘陷盆地与等效采高放顶煤方法是相同的。因此，固体回填开采沉陷预测的可转换到沉降预测与等效采高放顶煤方法。它可用于预测薄煤层的沉降参数。 固体回填法的沉降预测中，如何确定等效采高是问题的关键。固体充填采矿沉降影响因素的分析表明，等效高度影响的元素是：煤层厚度，顶板和地板灌浆，回填率，主要的回填体的压缩，残余压缩前的运动回填体等。然后计算等效高度可以分为两部分： 1）充填体（H）填充到采空区的高度，可以用下面的公式计算：H0=H (1) 其中是回填体和顶板之间的差距，是顶板和底板的运动，在灌装前，H是煤层厚度。 2）等效高度可以由以下公式决定：其中是剩余的固体充填体压缩率。Hz=HH0+H0 (2) 其中是剩余的固体充填体压缩率。固