| Coal bump is one of dynamic disasters in the field of coal mining which threatened safety of workers and apparatus. The frequency of coal bump increases with increasing of stope out, and the mechanism of coal bump is complicated.It is a difficult mechanical and engineering problem attract the interest of mining engineer and the scholar in this field.This article deserves the formation mechanisms of coal burst in the Xinzhouyao coal mine. Xinzhouyao coal mine is a mine of severely affected by coal bump. It has complicated geological conditions, thick coal seam, relatively hard coal seam and strong roof, and it is one of typical two-hard conditions of thick coal seam. In order to solve the problem, an investigation was carried out there and the result were as follows:(1)The bury depth of coal bump where it happened is relatively shallow compared with the critical depth. For example, the depth in 8518 at the East Third panel where coal bump occurred is about 320 m, and it is the shallowest depth where impact occurs in the Xi nzhouyao coal mine.(2) The impact of coal bump accident occurred at the beginning of the main coal seam mining is not so severe, along with the gradual increase of the gob area, the tendency of coal bump is also gradually increasing.(3) In the use of slice mining, coal bump occurs mainly in the thick coal seam mining under the layer face coal pillar roadway side in Xinzhouyao coal mine. When slicing above coal seam, the impact accident is less, and not obvious. Due to the limitation of geological conditions and mining technical conditions, using the hierarchical method mines thick seam in Xin Zhou coal mine. When slicing above coal seam, the occurrence of pressure in the mine is similar to the normal exploitation of other regions, periodic step distance from the old roof is 35~40 meters, and the record of coal bump accidents is less. But slicing below coal seam, the occurrence of coal bump is frequent, at this point, periodic step distance from the regeneration roof is 12~14 meters, which is 1/3~1/4 periodic step distance from the old roof, the influence of mining stress is obvious.(4)The impact pressure is always impact of roadway pressure, and happened in adjacent empty side of transportation lane. According to the statistical, the coal burst has occurred a total of 31 times in West 2 panel of Xin Zhou coal mine in 2010, 22 times in adjacent empty roadway, 7 times at working face, 1 time in roadway, and 1 time in minedout area block, occupying 70.96%, 22.58%, 3.23%, 3.23% respectively.(5)The coal burst accidents in Xinzhouyao coal mine have obvious regional characteristics. According to the regular of spatial distribution of the coal burst, indicates that mostly impact pressure accidents occurs in west second panel and east third panel of Xinzhouyao coal mine with larger destructive.(6) Xinzhouyao coal mine bump accidents and basic roof periodic weighting has obvious positive correlatiom time. The large intensity of mining would generate impact pressure. On the spatial location,the coal burst mainly in basic roof fracture location nearby. The two hard conditions basic roof cycle periodic weighting last long time when slicing(2~3days).The pressure is active while periodic weighting.(7)From the form of performance, the form of Xin Zhou coal mine burst is mainly overall launching with coal wall for skiving phenomenon, sometimes floor heave and big noise phenomenon occurred.Based on preliminary investigations and surveys, the mechanical properties of roof and coal seams in Xin Zhou coal mine were both harder than that in other coal mines. In order to quantitatively measure the hardness and impact tendency, the physical and mechanical test for coal and rock specimens collected from roof and coal seams was conducted respectively. The testing results showed that the hare property of roof and coal seams in this mine was existed, and the strong impact tendency was potential. In consideration of the impact tendency characteristic in this coal mine, combining physical testing, analog simulation and numerical simulation, the coal burst hazard mechanism was investigated under hard roof and hard coal seams(two-hard) conditions in Xin Zhou coal mine. Thus, the specific precautionary measures for coal burst could be adopted. The mainly achievements in this paper were shown as following:(1) By means of quantitative analysis for stiffness degree of roof in Xinzhouyao coal mine under physical testing, the two-hard characteristic in this mine had been finally determined. By uniaxial compression test, some mechanical parameters of coal and rock were obtained: the uniaxial compressive strength(UCS) of coal was 27.32 MPa; the elasticity modulus of coal was 2.20 GPa; the uniaxial compressive strength(UCS) of rock was 79.58 MPa; the elasticity modulus of coal was 21 MPa.(2) By means of theoretical analysis, the energy-domain size and feature was affected by roadway burial depth, rock stratum density, roadway radius, shear modulus of rock stratum and the volume of coal production.(3) Combining the physical and mechanics parameters and in-situ actual situation, the analog simulation model for the thick seam slicing system was established under twohard condition. The dimension of the model was 2,500 mm long, 200 mm wide and 1 300 mm high. The pressure cell was laid in the process of model building in order to monitor the change of stresses. Then, after the model was natural air-dry then was dismantled. After that the mining process began. The barrier pillars was set up at approximately 50 mm on both end of the model in coal seam; then the top slice was excavated first with a step of 50 mm. As the top slice was mined out, the bottom slice was excavated with the same excavation step successively, until it reached the margin of the barrier pillars. The stress data were collected by the pressure cells every 30 seconds synchronously as the excavation progressing.When stratified in mining, overlying strata fracture characteristics, migration rule and thick coal seam is similar. In the process of mining, mine pressure behavior is more obvious, the roof rock caving sequence from bottom to top gradually expanded, and the roof breaking way for single or multi layered caving. When the synchronization layer in 25 m. 2m thick sandstone roof first breaking, when mining 55 m 12m thick sandstone of basic roof fracture, the 15 m roof separation and failure, so the initial weighting is 55 m. mining 90 m 12m thick sandstone roof again broken, weighting is 35 m. The basic roof cycle breaking effect, the basic top 20 m within the scope of rock fissures, damage zone separation. When the layered mining face 120 m basic roof again broken, weighting is 30 m, the 35 m range of rock destruction and damage fracture zone. Under the development of stoping. The upper surface of the end, and the influence of breaking off again to slicing off again to again to again to 35 m regenerated roof caving height of 11 m mining to 50 m regenerated roof breaking to pressure step distance of 15 m. Mining 65 m regenerated roof breaking to pressure step distance of 15 m. Mining to 80 m, roof crush to pressure step distance of 15 m. Continued mining, advance to about 93 m, roof crush to pressure step distance is more than 13 M. when the working face advancing to 110 m, roof and breaking pressure. In the slicing process by stratified periodic roof separation and failure gradually to extend until slicing, the whole model damage propagation model.There should be many continuous peak stress rate curve, the peak point that overburden suddenly accelerated subsidence, and accompanied by a sudden release of energy. Each stress curves are large, a mistress has a certain peak time, time interval between each peak point, and a small peak to take a longer time to peak accumulation, the peak point on both sides of the stress change is relatively stable, the phenomenon that in fracture stratification of overlying strata in the process of turning a top slicing is more intense, sinking in the overlying rock caving process, periodic energy accumulation and release energy, when accumulated to a certain extent will suddenly release with overburden sudden sinking and collapse, in the process of coal under disturbance load damage is accumulated gradually, stability gradually decreased, while the coal load gradually increases, when the load exceeds the limit load of coal When the destruction of coal, coal for serious extrusion, bag and so on.Simulation results reveal two hard thick seam slicing mining should force and the change law of roof breaking rules: on the layering exploitation should force changes smoothly, except for periodic roof pressure outside basically no large fluctuations, and slicing mining, in the whole process of mining should force fluctuations are more severe, especially ahead of working face 0~40m should force fluctuation is one of the most severe. This is mainly due to the high layer working face goaf, roof rock breaking, rotary is not sufficient, and layered mining height, the fracture of the voussoir beam structure and below the rock gangue semi arch structure, rotary caused by violence.(4) By means of numerical simulation to simulate caving stress in the process of mining, energy and plastic damage development process. Simulation results show that: along with the advance of working face, coal pillar load in goaf is gradually increasing, the stress gradually increases, and to the adjacent working face, the head entry side air adjacent to a larger extent of stress concentration, even more than the ultimate compressive strength of the coal pillar; due to the damage characteristics of roof is hard and brittle, found in the mining process, development of plastic zone by shear failure than larger. Tensile failure is not obvious in the initial state, with the the area of hanging roof increases, tensile failure is obvious; in the mining process, when the hanging roof area is small, the maximum value appears in front of the coal wall stress, with the mining of hanging roof length increases, the maximum value appeared in the coal pillar goaf two stress Side;(4) working face front abutment pressure influence range is about 100 m, and are in good agreement with those measured in the field. The energy distribution and the stress distribution was the same.(5) The Xinzhouyao geological conditions of mining numerical model, which reveals the Xinzhouyao coal mine two hard thick coal seam coal bump. Simulation results show that Xinzhouyao coal mine coal bump is remaining after mining of upper coal seam coal pillar transfer to the lower coal seam stress and mining the synergistic action of stress results.(6) The Xinzhouyao coal mine coal bump mechanism, made according to the early warning measures and mitigation measures. Practice has proved, early warning and prevention measures combined can effectively avoid coal bump occurred. |
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