在综采覆岩移动规律类似的物理综采工作面开采及回填模拟外文文献翻译

英文原文Overlying Strata Movement Law in Fully Mechanized Coal Mining and Backfilling Longwall Face by Similar Physical SimulationH. Yanli, Z. Jixiong, A. Baifu, and Z. Qiang School of Mining, China University of Mining & Technology, Xuzhou, ChinaReceived August 7, 2011Abstract Fully mechanized coal mining and backfilling technology with gangue, fly ash and losses etc. changes the overlying strata movement characteristics and strata behavior law in the fully mechanized coal mining and backfilling longwall face (FMCMBLF). Based on the similar theory, a model of the overlying strata movement in FMCMBLF is established with sponge and plastic foam whose thickness ratio is 1:2 as the similar backfilling body. From the similar physical simulation, the following conclusions have been drawn: (i). The overlying strata movement develops from bottom to top as the mining progresses in the FMCMBLF and consequently, the subsidence curve of the strata assumes symmetrical bowl. (ii) No caving zone but only fissured and bended zones are found in the overlying strata herein. (iii) The subsidence velocity undergoes a changing process of “minimum, successive accretion, reduction, and stabilization,” and the overburden strata movement lasts for a long time. The test results would provide reference for further research of strata control as well as fully mechanized coal mining and solid backfilling technology.Keywords: overlying strata movement law, similar physical simulation, backfilling bodyINTRODUCTIONWith rapid development of national economy and increasing demand for coal resources in China, it is of great importance to study how to extract coal under buildings, railroads and water bodies. Fully mechanized coal mining and backfilling technology with gangue, fly ash and loess etc. is an effective method in this regard. It would not only effectively control the overlying strata movement and limit surface subsidence, but make full use of gangue, fly ash and other solid waste, thus providing a reliable and green mining technologic solution 1-4 to solve problems concerning coal mining, environmental protection and sustainable development of mining areas. In this technique, mined-out gobs(or gobs)are filled with gangue, fly ash and other solid waste as permanent supporting body to bear the weight of the overlying strata whose movement characteristics and strata behavior law are thus changed in the fully mechanized coal mining and backfilling longwall face(FMCMBLF) 5-10. In this sense, it is of great theoretical and practical significance to conduct further research with regard to overlying strata movement characteristics (OSMC) and strata behavior law (SBL) in FMCMBLF.Major methods to study OSMC and SBL are theoretical analysis, field measurement, numerical simulation, similar physical simulation, et al. Thereinto, simulation experiment with similar materials is an effective way in solving such problems and hence widely applied since specific problems may be addressed and valuable results may be achieved with the help of the test 11-16.Guided by the similar theory, the test uses structural physical parameters of similar materials and similar engineering models. By essence, it makes models of the overlying strata, which are reduced by certain rate, with similar materials to simulate coal mining and observe the movement and damage of the overburden.The experiment results herein are useful in analyzing and predicting characteristics of strata movement and deformation in actual mining. Among other items, similar physical simulation may, in the short term, reflect a comprehensive process of engineering mechanics and geotechnical deformation patterns. Its conditions are easily controlled and strata and surface movement directly perceived. In this sense, the simulation test is suitable for qualitative studies. The article herein takes sponge and plastic foam as similar backfilling body to simulate the OSMC 17 in FMCMBLF, thus providing reference for further research of strata control as well as fully mechanized coal mining and solid backfilling technology.1.SIMILAR PHYSICAL SIMULATION TEST OF OSMC IN FMCMBLF1.1. Model establishment with similar materialAccording to the mechanical characteristics of coal mining and solid backfilling, the model is reduced to be two-dimensional whose geometric length, thickness and height are respectively 2.5 m,0.2 m, 1.1 m and enrichment rate 100%. By analyzing a drill bore column next to the first mining and backfilling face of the fourth panel in southern Tunlan coalmine, we get its strata distribution as shown in Table 1.To better reflect the movement and damage characteristics of the overburden, the geologic column of the model is, to some extent, simplified and modified on the basis of real lithology in the panel. The similarity parameters of the simulation test are listed below the above similarity parameters, the physical and mechanical parameters and strata distribution of the model are shown in Table 2.In order to observe the strata movement at the face, six rows of monitoring lines are laid on the model from bottom to top, with a total of 87 monitoring points, as shown in Fig. 1. Thereinto, three lines are laid in the immediate and main roof above the coal seam where it is seriously damaged, with line spacing of 10 cm and point interval of 10 cm. The other three lines are set in the middle of each strata upward with point interval of 20 cm.Table 1. Real lithology in the panelStratumThicknessDepthNameStratum No.ThicknessDepthName123456780.6718.573.8313.570.416.725.60.6719.2423.0426.0439.6140.0156.7362.33siltstone gritstonepacksandcoalseam medium- grained sandstone mudstonesiltstone sandstone91011121314151611.6533.2513.83.510.2522.1418073.9876.9880.2394.0397.53107.78129.92309.92packsand gritstonefine-grained conglomeratefine siltstonefine-grained conglomeratefine-grained conglomerate weathered mudstone pedosphereFig. 1. Similar simulation model.1.2. Selection of similar materials as backfilling bodyOne of the key factors in truly reflecting the process of coal mining and backfilling is to select appropriate similar materials as backfilling body. Theoretically speaking, to simulate the dynamic deformation, the stress-strain curve of the simulation materials herein should be ensured to be similar with that of the actual filling body. In other words, the chosen simulation materials should be similar with filling body (gangue) in compression curve as well as the stress-strain curve computed by similar formula.To find the best backfilling materials, we herein choose sponge (Nos. 1, 2, 3, 4) and foam (Nos. 1, 2) of different strength, which have been measured by durometer, and compress them separately and jointly at their thickness ratio.Compression test of separate sponge and foam. Select sponges and foams of different types andpressurize them gradually until their limit to obtain respective stress - strain curve as shown in Fig. 2.Fig. 2. Stress-strain curves of different types of sponges and plastic foams: (a) sponge No. 1; (b) sponge No. 2; (c) plastic foam No.1; (d) plastic foam No. 2.Figures 2a and 2b illustrate that the strain values of compressed sponge alone are in line with those of the gangue under the same pressure if the load is small, however, when it increases to a certain amount, the strain values increase abruptly to the inflection point in Fig. 2. In addition, the final strain value, i.e. deflection value, is relatively large. In one word, their stress-strain curves vary widely with that of the actual backfilling body, so they are not suitable simulation materials.Foam No. 1 in Fig. 2c is of heavy strength and therefore its strain value barely changes as the load pressure increases; however, the stress-strain curve of foam No. 2 is almost lineal and the according strain value continues to mount even under ultimate load, indicating that its is far from a stage of compaction. Therefore, they are unfit for the simulation test as well.(a)(b)Fig. 3. Stress-strain curves of compositions of sponge and plastic foam of different types: (a) sponge No. 1 and plastic foam(a)(b)Fig. 4. Stress-strain curves of different proportions of sponge and plastic foam: (a) sponge No. 1 and plastic foam No. 1 by a ratio of 1:2; (b) sponge N. 1 and plastic foam No. 1 by a ratio of 1:3.Fig. 5. Comparison of stress-strain curves derived from computing and experiment.In this condition, a composition of foam and sponge is taken into account for the compression test. Compression test with compositions of sponge and foam. Combine sponge No. 1 of the greatest strength with foam No. 1 and No. 2 respectively pro rata of 1:1. Their test is conducted under the same ultimate load and the results are shown in Fig. 3.The curve in Fig. 3 indicates that since sponge is relatively weak in intensity, the strain value of its composition with foam floor, both No. 1 or No.2 is larger than that of the gangue in the site when the load pressure increases gradually. Therefore, the thickness ratio between sponge No. 1 and foam No.1 is adjusted to be 1:2 and 1:3 respectively and their curves under the same ultimate load pressure are shown in Fig. 4. An analysis of Fig. 4 shows that when the thickness ratio is 1:2, the according curve is similar with the one obtained by testing the mechanical properties of gangue, which is noted in 4. Figure 5 whereafter is a comparative analysis between the curve in Fig. 4 and the one computed by similar formula.By comparison, the stress-strain curve in the simulation test is essentially similar with the computed one in terms of both changing process and the final strain compression values. Hence, the simulation filling body in the test is the composition of sponge No. 1 and foam No. 1 pro rata of 1:2.2. ANALYSIS OF SIMULATED OVERLYING STRATA MOVEMENT WITH SIMILAR BACKFILLING MATERIALS2.1. Strata movement and failure characteristics in mining processIn the process of simulated mining with solid backfilling, the overlying strata as a whole remain undamaged, maintaining the overall continuity. No distinct caving zones but only fissured and sagging ones are found in the strata. No obvious abscission layer above the strata, either. Fracture mainly occurs on the open-off cut and stopping line side, assuming symmetrical “” distribution in a small range. No vertical but small horizontal cracks among layers appear at the face, which have been gradually compacted as the face advances. Based on the extent to which the overlying strata are displaced and damaged, the simulated mining process is divided into two phases.Fig. 6. Strata movement and failure process at the first solid backfilling phase under various face advancing: (a) over 20 m; (b) over 40 m; (c) over 70 m; (d) over 80 m.Fig. 7. Strata movement and failure process at the first solid backfilling phase under various face advancing: (a) over 90 m; (b) over 120 m; (c) over 150 m.Phase 1: there is no distinct sagging in the roof and the compression value of the backfilling body is small. The strata movement and failure process (as the mining proceeds over a distance of 20, 40,70, and 80 m) is shown in Fig. 6. Phase 2: there is obvious sagging in the roof and the compression value increases. As the roof continues to sag, there are slight rock failure and fracture, the detailed process (as the mining proceeds over a distance of 90, 120, and 150 m) is shown in Fig. 7.2.2. Dynamic characteristics of the monitoring points displacement in mining processObservation and analysis of monitoring points displacement on the same vertical line. Figure 8 isthe subsidence curve of monitoring lines at different time. It shows that the overburden movement develops from bottom to top. As the face advances, the subsidence values and ranges gradually increases till it becomes stable as a symmetrical bowl. Supported by backfilling body, the monitoring points herein sink in a mild and almost synchronous manner, indicating that there is no wide abscission layer among the lines. Among other items, the vertical displacement of the roof varies with their distance from the coal seam. The closer they are, the larger their displacement is. But the displacement gap/disparity between monitoring lines are very limited. Choose monitoring points of maximum subsidence herein on line No. 1 (70 m from the roof) and No. 6 (10 m from the roof), respectively, namely point No. 81 and No. 11. Figure 9 are curves concerning their subsidence values and velocity as the mining progresses.Fig. 8. Subsidence curves of different monitoring lines at different time: a12th observation during mining operation; bafter mining.Figure 9 below illustrates that the subsidence velocity of the overburden herein undergoes a changing process of “minimum, successive accretion, reduction and stabilization,” which is basically consistent with that of the longwall caving except that the subsidence values and velocities of the former method is much lower than the latter one. When the face advances over 70 m, the subsidence velocity of point No. 81 picks up and reaches its maximum, 19 mm/d, 90 m ahead of the face. Thereafter, point of the maximum velocity moves forward with the face, whereas the subsidence rate at point No. 81 gradually decreases and finally levels off. Compared with longwall caving method, FMCMB herein, due to the support of backfilling body, may permit the overburden subside in a mild manner whose maximum velocity lasts for a short time. However, as the backfilling body is compacted step by step, the overburden strata herein move for a longer period of time, which implies exactly that backfilling body plays a role in strata control by deforming the strata homogeneously.Observation and analysis of monitoring points displacement on the same horizontal line. As the face advances, subsidence displacement of the overburden gradually increases, as shown in Fig. 10. At the early stage of coal mining, the monitoring points remain almost unmoved because of the supportive backfilling body and roof beam of a certain strength. However, when the face advances over 70 m, monitoring points at the bottom begin to sink and the subsidence spreads from bottom to top as the backfilling body and roof become deformative and bended under pressure.Thereafter, the values and ranges of subsidence increase gradually with the face advance. However, since the gobs are filled with backfilling body, which support the overburden and thus reduce the free space of the roof, dynamic subsidence of all monitoring points are relatively mild, avoiding abrupt increase and strata cavings. Meanwhile, their subsidences are almost synchronic, resulting in no big abscission layers. According to the results of observation, the final maximum subsidence values of the six monitoring lines are, respectively: 1226 mm (60 m above the roof),1294 mm (50 m above the roof), 1345 mm (40 m above the roof), 1389 mm (30 m above the roof),1482 mm (20 m above the roof) , 1486 mm (10 m above the roof). The subsidence curve herein is bilaterally symmetrical and essentially consistent with that of the longwall caving method.Fig. 9. Subsidence curves and velocities at the maximum subsidence point on different monitoring lines: (a) point No. 81; (b) point No. 11.Fig. 10. Dynamic subsidence curves of different monitoring lines: (a) line No.1; (b) line No. 2; (c) line No.3; (d) line No.4; (e) line No.5; (f) line (a)(b)Fig. 11. Vertical strain curves among different monitoring lines: (a) between lines Nos. 4 and 5; (b) between lines Nos. 5 and 6.During the process of mining and solid backfilling, rock failure mainly occurs in surrounding strata of the coal mass. Hence, we choose monitoring lines Nos. 4, 5, and 6 herein to observe their vertical strain changes, as shown in Fig. 11.Vertical strain changes are quite abrupt near the open-off cut (5070 m) and stopping line (180200 m) at the simulated face herein, indicating that strata in the region subside nonuniformly and result in obvious abscission layer therein. In contrast, the vertical strain changes in the middle area of gob (70180 m) are relatively small and mild, showing that the strata there subside synchronically without causing obvious abscission layer.1. To simulate the dynamic deformation, composition of sponge and foam is taken as filling materials in the similar simulation test as a result of contrast experiment. According to the experiment, the stress-strain curve of the composition above, when the thickness ratio of sponge No. 1 and foam No. 1 is 1:2, is similar with gangues compression curve as well as the stress-strain curve computed by formula. Hence, it is reasonable to choose the composition above as similar simulation materials.2. In the process of simulated mining with solid backfilling, the overlying strata as a whole remain undamaged, maintaining the overall continuity. No distinct caving zones but only fissured and sagging ones are found in the strata. Fracture mainly occurs on the open-off cut and stopping line side, assuming symmetrical “” distribution in a small range. In this sense, solid backfilling limits the occurence of caving, fissured and sagging zones in overburden as well as the generation of abscission layers, which is an important display of the role backfilling body