| The research is conducted in island coal safety, efficient recovery which is ubiquitous in Kailuan Group. To make T1391 isolated coal in Tangshan mine as a research background, mechanics mechanism, mining technology and prevention measures is studied direct at double goaf island coal mining face bump. Three methods are applied in the whole study including theoretical analysis, numerical simulation and field measurement.Combining the situation of China’s coal industry, islands coal recovery significance is expounded in paper and it is supposed that the recovery is of importance for the country resource sustainable development, especially in eastern region. Due to island coal under the influence of several side goaf, stress concentration and energy-storage occur on the coal body and bump is easy to be caused during the island coal mining. So paper is summarized to rockburst occurred theory, control technology, rock burst occurrence theory of island coal mining face, evaluation and control by collecting a large of literature. On that basis, the research contents, methods and technical route is determined.In order to protect the isolated coal in the safe and efficient recycling, research is conducted on overlying strata mechanical mechanism of residual islands coal body. For face T1391 studyed on the belongs to the bilateral goaf island coal, double goaf island coal mining face mechanics model of overlying strata is established and analytical solution for bending moment id made a distribution computational analysis; Combine island coal T1391 including a large coal and a small one and 义modeling research of pillar dimension to bearing stress distribution, distribution of bending moment and concentrated stress P; Then on that basis, introduce possibility of impact coefficient and genetic energy theory as judging mechanism to double goaf island coal mining face bump occurrence and achieved some specific research results in this part:(1) Establish Mechanical model of double goaf island coal mining face roof by applying mechanics theory of elastic thin slab and reciprocal theorem of work, i.e. the roof is clamped to the side and simply-supported at both ends before the initial fracture occurs; the roof is simply-supported at both ends, one side fixed and one side free after the initial fracture occurs and analytical solution for bending moment distribution is obtained for-0.640221 m and-0.162962 P respectively.(2) On the basis of research conclusion from(1), deduced and established bearing stress distribution of different size of coal pillar and calculation formula and method of the partition. Then achieved bending moment distribution for different size of coal pillar and be coincidence with formula:At the same time, it is found: that peak bending moment is existence in both sides of isolated island pillar and original state still keep in central of islands pillar when field stress is existed in pillars center; that peak bending moment is still existence in both sides of isolated pillar and Larger values of bending moment distribution is kept in center when the elastic stress rising areas is existed in pillars center; that bending moment distribution is tending to the maximum in the entire inside the isolated island pillar when isolated island pillar is in the overall limit state.Due to prevention of rockburst, the large size of isolated coal pillar against small area The small size of the isolated coal pillar for comprehensive prevention, it is determined that Isolated island coal make primary recovery within the area of T1391(3) Bearing expression of overburden rock broken after cracking is deduced and it meets:(4) On the basis of the foregoing conclusion of the study, isolated coal in the energy calculation expression is further obtained, i.e. the expression is corresponded before the first fracture of roof occursAfter the first fracture of roof occurs, it meets:At the same time, combining energy accumulation expression, it is found that the influence of overburden roof fracture spacing is not evident when the bilateral goaf island coal is energy-storage, i.e. Under the influence of double side goaf, energy change from roof fracture can be neglected. Meanwhile, on premise of the same development height for crack zone, energy accumulation of coal thickness change mined for one time is not also obvious.We were further computing research for the bilateral Tangshan Mine Mined island of mining coal and rock burst prevention and control technology on the basis of the aforementioned studies. The research content including partitioning isolated coal mine in Tangshan, the theoretical analysis of coal pillars left specific research division and advanced drilling program with parameters of relief to identify risk areas, the conclusion is as follows:(1) We Obtained the area of the broken pillar range from 2.9m and the limited equilibrium zone range from 4.53 m by calculating,so it can keep 3-4m of Pillar from along goaf viewpoint. Further, the mutation from pillar, buckling to pressure angle impact occurs proposed coal pillar size is greater than 10.3m.(2) When we get to stay more than 10 m wide set of pillar coal central pillar supporting two-way influence will inevitably be superimposed pressure, by combination with the aforementioned calculation method surrounded pillar energy distribution, and calculated UW=3.06×105J, while leaving in coal 3m column, UW=1.173×105J, small coal pillar leaving in 3m width of only 38.3% over 10.3m pillar of energy. Therefore, the regional measures can be significantly improved when the isolated coal pillar recovery rockburst the probability of occurrence.by using only pillars.(3) From isolated coal pillar beginning mining to consider making local preventive measures, in bilateral mining empty island coal pillar on both sides of the additional moment position around the 0.05 L range reached maximum positive and negative bending moment, so in terms of energy or from the gradient, this area are focus of rockburst prevention.(4)When roof occurred after the initial fracture, stress affected lateral support of its energy accumulation than 105 J calculated and analyzed, respectively, limit equilibrium analysis of the area and the elastic region, obtain from the mined-out area is 4.22m-31.83 m rockburst danger zones occur. Once again, the island bilateral Mined coal mining conditions, the use of hazardous area along goaf can avoid the rock burst occurred.(5) The working face mining by drilling pressure relief control measures for the calculation and analysis, points out that the borehole pressure relief scheme, the use of 100 mm and 200 mm borehole diameter and 1m or 2m borehole spacing and 10 m, 15 m, 20 m, 25 m and 30 m drilling depth, to further determine the pressure relief drilling parameters of the experimental study of basic parameters are presented.In order to verify the above theoretical research results and determines the final pressure technology and parameters, the use of computer simulation software to simulate FLAC3 D research, including the study of coal pillar stability, danger zones, ahead of the mining methods for determining the relief borehole parameters Select several aspects, we get the following conclusions:(1) We can found that width is 5m coal pillars, the recovery has been destroyed and pressure relief on stress distribution of different size of coal pillar supporting numerical simulation study; and left 10 m supporting pillar of, coal pillar elastic core in the process of mining face because of posterior continuous mined out, supporting the stress gradually increased, and the peak force should be with the working face advancing gradually moves forward; when the coal pillar width to 15 m, due to decrease of the elastic core damage, supporting coal pillar stress increases gradually, the pillar stress concentration increasing, the impact of instability risk is higher.We can found that when the coal pillar width is 5m when plastic failure and 10 m, in the range of face 60 m with the mining recovery work, Pillar had already occurred to some extent for different coal pillar size of plastic zone simulation. Leaving in 15 m Pillar situation has improved, but short duration. Leaving in 20 m and 25 m wide at Pillar, the elastic core in the middle of the recovery process of a high bearing stress concentration, the impact of pillar instability occurs significantly increased risk.To simulate different coal pillar energy distribution found, leaving in 5m Pillar under the influence of roof support stress recovery Now that the initial damage occurred, relief, release of elastic energy accumulated in pillar premature; with increase the width of the pillar, pillar gradually played a supporting role in the internal pillar elastic energy accumulated gradually increased. When coal pillar width 10 m, the face with the mining, coal pillar working face near accumulate more energy, indicating that this area is more concentrated coal pillar stress, shocks occur gradually increases the risk of instability. Similarly, coal pillar width varies from 15 m to 30 m, intra-regional pillar near the roadway appeared banded energy accumulation region which moves with the face in front of work mining, banded region gradually expanded, it can be seen, in the region of the elastic pillar near the roadway can accumulate more, with the face forward, prone to the impact of instability.Therefore, the simulation of various types of coal pillar of different sizes were found, leaving in small coal pillars or no pillar of effective measures to improve the island pillar impact earth pressure in the face, combined with the previous theoretical research, recommendations T1391 isolated coal pillar recycling uses along goaf.(2) At different coal pillar size of research premise of the danger zone island face mined period studied, found that the initial break before the roof collapse, peak stress and the risk of regional distribution in the region on both sides of the roadway, which the establishment of the aforementioned side simply supported, clamped on the side of the mechanical model is consistent, that is, before the first fracture occurs in the roof need to prevent entities on both sides of the roadway and coal pillar rock burst occurred. When Overburden rock fracture, the energy accumulates mainly in the central position ahead of the working face, so the need to develop appropriate technical measures to prevent the occurrence of Face rock burst, such as may be used to improve the working resistance of hydraulic supports and other technical measures.(3) Combined with improved drilling ahead relief of stress distribution and coal energy accumulation of technical parameters of the relief holes to the simulation of the actual situation of the mine thinks, should be drilled aperture 200 mm, drilling and drilling depth spacing 1m 15 m of relief programs.(4) Combined with special thick seam mining methods, leaving in 3m pillars along goaf layered with top coal caving mining simulation, simulation using the optimal technical solution and parametric drilling relief, research found that the use of two top coal caving roadway stress distribution is similar and relatively small slice mining layering top, more concentrated distribution, analysis of the reasons that the top Slice Slicing directly affected by the roof, and that the use of discharge caving mining superior top slice mining layering situation.Finally, based on the research contents and achievements from theoretical research and numerical simulation experiment, double goaf island coal mining recovery face T1391 in Tangshan is evaluated in ground pressure observation and rock burst hazard. The achievement is following:(1) coal seam 8-9 bear with above average in shock hazard in Tangshan Mine face T1391 which belong to ouble goaf island coal mining and buried depth of coal face is over 530 m of rockburst occurrence. So when the face recovery, the risk of dynamic instability exits.(2) Based on analysis for roadway deformation to bearing stress in advance, 20 m is achieved for peak position of face bearing stress in advance and from the view of the goaf side support stress superposition, This area is the focus of prevention.(3) Roof activity intensity is confirmed on the basis of roof abscission layer study and roof dramatic range is 16-28 m from the face.(4) In the observation of hydraulic support working resistance, the conclusion for bottom of the face area > top of the face area > middle of the face can be obtained, which is different from a regular face in the middle of the stress that is larger than the both sides and it prove the conclusion that the prevention focus of aforementioned island coal mining face is on the both ends of working face(5) Based on the measured amount of cuttings, the cuttings is close approximately to medium risk lower limit and the phenomenon of sound and sticking is accompanied before first weighting come. Comparing other face in engineering analogy, it belongs to middangeard but cutting significantly reduced.So it can be deduced that roadway driving along goaf and pressure-relief boreholes play a role in engineer; Cuttings is more within 20 m of face advanced and there was little more than risk- free limit and almost no dynamic phenomenon took place after roof broke for the first time, so it is dynamic risk-free. Aforementioned study concerning for comprehensive prevention before roof first weighting is proved and the phenomenon of rib spalling in face exists without dynamic instability danger after roof pressure happened. The region of two roadways advanced 20 m in face, however, belong to superposition areas for advanced stress and goaf lateral stress and its prevention is important.Some innovations is achieved in paper:(1) Establish mechanics theory of elastic thin slab model for double goaf island coal, i.e. he roof is clamped to the side and simply-supported at both ends before the initial fracture occurs; the roof is simply-supported at both ends, one side fixed and one side free after the initial fracture occurs and analytical solution is achieved. It is achieved that peak position of bending moment located in both ends of the face with 0.05 times before roof break and peak position of bending moment in face center after roof break, which is prevention focus area of rockburst.(2) Establish computing formula for energy accumulation of different sizes islands coal based on research concerning bearing stress distribution and partition in different size of coal pillar. Meanwhile, with the influence by bilateral mining, roof breaking stride has a little impact on energy-storage in islands coal mining.(3) Combining distribution characteristics of bending moment after isolated coal roof happened to break, Roof load expression of three sides goaf is deduced.(4) Combining the actual parameters of islands coal and its calculation, two kinds of leaving of chain pillar are proposed firstly, i.e. The first one is to leave 3-4m small coal pillars for roadway driving along goaf; The second one is to leave over 10.3m roadway of coal pillar to prevent rockburst occurrence result from mutations of coal pillar. The accumulation energy in coal pillar of roadway driving along goaf is merely 38.3% to the one leaving over 10.3m coal pillar by energy calculation and it is held that roadway driving along goaf is the most effective regional control measures to prevent rockburst occurrence. |
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