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1、外文资料与中文翻译外文资料：Principle and engineering application of pressure relief gas drainage in low permeability outburst coal seamAbstract: With the increase in mining depth, the danger of coal and gas outbursts increases.In order to drain coal gas effectively and to eliminate the risk of coal and gas outbu
2、rsts, we used a specific number of penetration boreholes for draining of pressure relief gas.Based on the principle of overlying strata movement,deformation and pressure relief,a good effect of gas drainage was obtained. The practice in the Panyi coal mine has shown that, after mining the C11 coal s
3、eam as the protective layer,the relative expansion deformation value of the protected layer C13 reached 2.63%n, The nermeabilitv coefficient increased 2880 times, the gas drainage rate of the C13 coal seam increased to more than 60%, the amount of gas was reduced from 13.0 to 5.2 m3/t and the gas pr
4、essure declined from 4.4 to 0.4 MPa, which caused the danger the outbursts in the coal seams to be eliminated. The result was that we achieved a safe and highly efficient mining operation of the C13 coal seam.Keywords: protective layer mining; technology principle; drainage of pressure relief gas; e
5、ngineering application1 IntroductionWith an increase in mining depth, the amount and pressure of gas increases, gas disasters are becoming more serious and several shallow and non-outburst coal seams are gradually becoming outburst coal seams. Today, China has become the country with the most seriou
6、s coal and gas outburst disasters in the entire world. Globally, our frequency and intensity of outbursts are the most severe. In contrast, coal and gas outbursts coal mines had been stopped production in the USA, Australia, Russia and other countries. According to a statistical analysis by expert c
7、onsultants in 2005, among 415 coal mines of the 45 major monitored state owned coal enterprises, 234 mines are high gas and outburst coal mines, accounting for 56.4% of the major coal mines and 142 mines are subjected to coal and gas outbursts, accounting for 34.2%.Usually, the permeability coeffici
8、ent of outburst coal seams is low. For example, on average, this coefficient in the C13 coal seam of the Huainan ore area was only 0.011 m2/(MPa2.d), which presented great difficulties in pre-drainage of gas and in gas control to prevent outbursts in coal seams. Based on the current condition of coa
9、l seams in the Panyi coal mine, we adopted a protective layer in our mining technology to drain pressure relief gas from protected seams,using RC net penetration boreholes in floor roadways, effectively reducing its gas content, completely eliminating the danger of outbursts and achieved safe and hi
10、ghly efficient mining conditions.2 General situation of test areaThe Panyi coal mine is a large mine designed for 3Mt production capacity. The C13 coal seam is one of its primary and most productive coal seams, which contained a large amount of gas under high pressure.A large number of outburst acci
11、dents have formerly occurred during mining, including a major gas explosion, so control over coal gas was very urgent before we could exploit this coal seam.The test area was located between the East-1 and East-2 mining areas, with the B 11 coal seam as a protective layer. We planned to combine mini
12、ng the 21511 working face in East-1 and the 23521 in East-2 and called the combination 23521 instead The strike of the face is 1640 m and the trend 190 m.The thickness of the coal seam is between 1.52.4 m,2.0 m on average and the dip angle 60-130, 90 on average. The amount of gas of the B11 coal sea
13、m is 4-7.5m3/t and it is a non-outourst coat seam.The coal seam is stable and its geological structure simple.Fully mechanized coal mining technology had been adopted for the working face, designed for 2000 t/d.The C13 coal seam is a protected layer, located 70m above the B11 coal seam. The correspo
14、nding test working face of the protected layer consists of the 21213 working face in East-1 and the 23223 in East-2 (called 21213/23223 combined). The strike is 1680 m (two faces in all) and the trend is 160 m.The coal seam is 5.576.25 m thick, 6.0 m on average,the dip angle 60130 and 90 on average.
15、 The original measured gas pressure was 4.4 MPa, the amount of gas 13.0m3/t and the original permeability coefficient only 0.011 m2/(MPa2.d). The coal seam was also stable and its geological structure simple. By draining the pressure relief gas, the danger of outbursts in the C13 coal seam could be
16、eliminated and the amount of gas was effectively reduced.A comprehensive，mechanized cover caving coal mining technology been adopted for this working face, which was signed for 5000 t/d.3 Drainage principle of pressure relief gasDraining of pressure relief gas is referred to as protective layer mini
17、ng technology. When we mine coal seams in outburst coal mines, we should first mine the non-outburst or low risk outburst coal seams as protective layers, where the outburst coal seam is then called the protected layer. With protective layer mining, the coal and rock mass among the roof and floor mo
18、ves and deforms within certain limits,which causes stress changing. Fracture fields are redistributed, ground stress is reduced, the coal seam expands, the coal seam permeability coefficient increases and drainage condition are created for pressure relief gas in the protected coal seams. In the case
19、 of the Panyi mine, we drilled penetration boreholes or carried out surface well drilling to drain the pressure relief gas, which caused the amount of gas and pressure to decrease significantly and the coal mass turned hard. Naturally. eas pressure reduced to below 0.5MPa, the amount of gas reauced
20、to below a 6m3/t and the coal consistency coefficient rose 48%-100%.At the end, the danger of outbursts was completely eliminated from the protected layers and conditions for safe and highly efficient mining had been achieved. Drainage indices of pressure relief gas in the different ore areas are sh
21、own in Table 1.4 Drainage methods of pressure relief gasDrainage methods of pressure relief gas consist largely of draining gas from the protected layers affected by mining. The space between the protective working faces 23521 and 21213/23223 was about 70 m, which is really a long distance below the
22、 protective layer mining. We have often used surface well drilling and upper penetration boreholes located in floor roadways to drain pressure relief gas from the underside of the protective mining layer. Surface well drilling is unreliable and we often used penetration boreholes. The design of pene
23、tration boreholes includes the construction of a floor roadway, a suction drilling field and upper penetration boreholesAll construction activities should be completed before starting mining the protective layer and we should ensure that the pressure relief gas has been drained simultaneously with m
24、ining the protective layer.4.1 Design and construction of the floor roadwayBased on the occurrence of coal strata and concrete geologic conditions, the floor roadway was located 10-20 m below the C13 coal seam in a good lithology rock bed and 4656 m from the protective layer.On the one hand, this po
25、sition assured safe excavation, avoided gas inrush from the C13 coal seam and prevented the excavation of another coal seam by mistake. On the other hand, this location did not affect the mining of the B11 coal seam and assured normal functions for gas draining. The floor roadway was located in the
26、middle of the working face of the protected layer on the strike where,in principle,one should insist on avoiding forming down holes.The proportion of the section of the floor roadway was designed for 6 m24.2 Design and construction of the suction drilling fieldAt working face 23223, 51 fields had be
27、en constructed west forward and away from the stopping line in the floor roadway under the C13 coal seam. In the pressure relief area, a field was set every 40 m, so the pressure relief area of face 21213/23223 in the protected layer needed 39 fields in all. According to the pressure relief angle, n
28、on pressure relief areas were present in the protected layer, with a field every 10 m, so that the non pressure relief areas of face 23223 in the protected layer needed only three fields and nine in face 21213. The drilling field was perpendicular to the floor roadway,with a length of 5m and a net s
29、ection proportion of 6.16 m2 Bolt-shotcrete support technology had been adopted.4.3 Design and construction of upper penetration boreholesEvery drilling field had 4 holes set on the strike in the pressure relief area. The space between holes was 40 m, which was oriented on the middle of the thick-su
30、rface of the coal seam. The position of the hole opening was located at the top of the drilling field and the final hole position ended 0.5 m into the roof of the C13 coal seam. Its design is shown in Fig.1. The total length of the draining holes was 8879 m,of which 1460 m was drilled through the C1
31、3 coal seam. The space between holes was 10 m in the non pressure relief area.5 Pressure relief levelAfter mining the protective layer, this layer moved and deformed, which caused ground stress to reduce,the permeability coefficient to increase and pressure relief occurred. Pressure relief levels ar
32、e related to the space of the layer, rock lithology, mining height and so on. The levels are higher and the pressure relief effect is better in the protected layer. The change of ground stress can visibly reflect the pressure relief level, but the stress is hard to measure in the field, so we adopte
33、d the extent of coal deformation and the coal seam permeability coefficient to reflect the level indirectly.5.1 Relative deformationWe adopted a base point method to investigate the deformation of the C13 coal seam. To start, we drilled a deep hole, and then installed test points in the roof and flo
34、or of the C13 coal seam, where the deformation was determined by the relative displacement of the two test points. The measured results are shown in Fig.2. We can see that, during mining of the B11 coal seam, the C13 coal seam was first compressed, and then expanded, the maximum compression deformat
35、ion was 27 mm and the maximum expansion deformation 210.44 mm, so that the maximum relative compression deformation was 0.337%, and the maximum relative expanding deformation 2.63%. The bigger the expansion deformation, the better the effect of pressure relief.5.2 Variation of permeability coefficie
36、ntThe orieinal coal seam nermeabilitv coefficient was only 0.011m2/(MPa2.d).After mining the B11 coal seam, the pressure was relieved from the C13 coal seam and the permeability coefficient clearly increased. By using the amounts of residual gas and the borehole gas inrush, we calculated that the pe
37、rmeability coefficient had increased to 32.687 m2(MPa2.d), an increase of almost 2880 times, which indicated that the C13 coal seam was now in the condition where gas has been drained.6 Drainage effect of pressure relief gas6.1 Amount and rate of gas drainage1) Analysis of drainage of pressure relie
38、f gasWhen the protective working face advanced 40 m over the suction drilling field, the amount of gas drained rapidly increased. Fig.3 shows the variation in the amount of gas drainage vs.time in the drilling yard of the Huainan coal mine. The original 20 days was the period of increased gas draina
39、ge, enhanced pressure releasing activity and the amount of gas drainage increased. The period between 20-80 days was the active period of gas drainage, the pressure release activity became regular and permeability reached a maximum. Gas drainage was regular and the amount of gas drained from a singl
40、e hole was over 1.0 m3/min. After day 80 the attenuation period set in, where the coal seam became gradually compacted, permeability reduced, the residual pressure became small and the amount of gas drainage reduced exponentially. According to this research, a highly effective drainage period was 2
41、months, the length of the affected area was 160 m and the number of active drainage holes was 16. On average, the amount of gas drained from a single hole was about 1.0 m3/min Aftter 4 months of continuous gas drainage ,the rate of gas drainage reached over 60%.2) Total amount of gas drainage and am
42、ount of residual gasThe total amount of gas drainage includes the amount drained from penetration boreholes and wind emission in the floor roadway. The period of working face 21213 for which statistics were obtained was from Feb.1, 2000 to Jan. 31, 2001, 365 days in all.The accumulated amount of gas
43、 drainage by penetralion boreholes was 7.99Mm3 and the amount by wind emission 0.74 Mm3.The reserves of the protected layer were 14.68 Mm3 and the total amount of gas drainage 8.73Mm3,so that the rate of gas drainage reached 60%. The amount of gas inrush and amount of gas flowing into work-out areas
44、 of the protective layer were not inccluded in our calculation, so that the actual rate of gas drainage was larger than the calculated value,i.e.,a rate over 60%. Since the orieinal amount of eas of the C13 coal seam was 13m3/t. the restauai eas content was 5.2m3/t, given our calculations.6.2 Gas pr
45、essureWith the advancement of the working face, the pressure gauge value gradually decreased from 4.4MPa, when the working face was 100 m away from the pressure measured hole; when 80 m away, the pressure sharply decreased, and at 62 m the pressure gauge finger pointed to zero. When the protective w
46、orking face advanced 400m past the pressure measured hole, the pressure value increased from zero to 0.4 MPa and remained stable, which indicated that the residual gas pressure was 0.4MPa.6.3 Outburst danger eliminated analysis of the protected layerThe amount of gas in the protected layer is decrea
47、sed by draining the pressure relief gas.The amount of residual as of the C13 coal seam was reduced to 5.2 and the residual declined to 0.4 MPa. The amount of gas pressure values were lower than the critical value, which was 8m3/t for the amount gas and 0.74MPa (pressure gauge) for gas pressure.All t
48、his shows is that C13 coal seam had changed from a high gas and outburst coal seam to a low non-outburst coal and C13 became a safe and highly effective coal seam where mining conditions became considerably better, as proven by its current mining practice.7 Conclusions1) With the advancement of a wo
49、rking face, coal and rock masses among the roof and floor move and become deformed within certain limits, ground stress is reduced, coal seams expand and the coal seam permeability coefficient increases in outburst coal seams. After mining of the Bllcoal seam, the maximum relative compression deformation of the C13 coal seam was 0.337% and the maximum relative expansion deformation 2.63%. The permeability coefficient increased almost 2880 times and favourable conditions for drainage of
