Advanced Materials Research Vols. 361-363

Abstract: The properties of a longitudinal guided wave with central frequency 5kHz propagating in partially grouted rock bolts were studied by experimental and numerical simulation methods. The guided wave was excited by the impact–echo method on the free end of the bolt, and the excited wave measured in the experiments was used as excitation input in the numerical simulation. The numerical results match well with the experimental ones. Two empirical formulas were obtained for when the reflected waves from the upper interface and from the embedded end of the bolt could be distinguishably detected. Conclusion is drawn from the simulation results that the guided wave energy velocity in the embedded section of the bolt increases with the increase of elastic modulus of the grout media. A new method was proposed for anchorage quality testing and its effectiveness was proved by a testing example.

Abstract: In this paper, the implementing method of updating the coal mining area’s DEM by mining subsidence forecast data is introduced. The data file of mining area’s elevation points can be generated by extracting from the digital topographic map of coal mining area, and after the interpolation and encryption of extracting mining area’s elevation points, the data file of the mining area’s collapse can be obtained by subtracting the values of the subsidence forecast from the elevation values of the mining area’s elevation pionts. According to the data file of the mining area’s collapse, DEM of the mining area’s collapse can be generated, and the corresponding contour map can be also generated. This has important significance for the environmental management and disaster prevention engineering design of coal mining area.

Abstract: According to the mining conditions and equipment level of Xingshan iron mine, optimization research on the stope structural parameters of sublevel caving was made, and finally adopted the structure parameters with 15m sublevel height and 20m drift interval. In order to find out the rational independent advance of ore breaking under 15m×20m structural parameters, theoretical arithmetic and industrial tests were carried out. The tests show that the rational independent advance of ore breaking drift interval should be 3.4m, and the optimized structural parameters of 15m×20m×3.4m has excellent effects on reducing mining cost and improving mining recovery rate.

Abstract: The showing of ground pressure is severe in workface of coal seam with thin upper cover, due to the thin upper rock seam and the action of upper incompact cover. Generally, the thin cover coal seam with 90m upper cover can be defined as Coal seam with thin cover. The result of simulation experiment for workface with thin cover and 5m mining height shows that under overburden pressure, the step subsidence is obvious, and balanced structure is still formed in surrounding rock, under overburden pressure. But the shape and form of balanced structure are different from the balanced structure formed upper coal seam with normal buried depth. There appears step or dislocation between the upper rock seam in workface and the balanced structure in the mined-out area, and the quantity of dislocation is 2m. But no step subsidence appears in the simulation for the workface with thin cover and 3m mining height. So the mining height is the key for the step subsidence. This paper gives out the movement model of surrounding rock upper the workface in thin cover coal seam and chooses 1 MPa as the support capacity for the first workface of Gaotouyao Colliery based on calculation.

Abstract: Based on the numerical simulation method and actual measurement analyses, characteristics of working face mineral pressure of the River Mouth Mine has been analyzed and this paper has obtained the following results: First weighting step of the main roof is 23.2 m, the average dynamic pressure coefficient is 1.54~1.74, mine strata behaviors is fiercer; hydraulic prop’s average working resistance is 45.72 KN of each, which indicates hydraulic prop’s working resistance has larger surplus coefficient, some measures should be taken to increase utilization ratio; advanced support length of return airway and mechanical roadway should reach to 30 m, the method and results can be used to improve support pattern of working face and guide safety production.

Abstract: Based on green mining idea, this paper developed a kind of filling material with coal gangue as coarse aggregate and designed underground-preparation system with the main processes being breaking, mixing and pumping. As a result of the research, the coal gangue pollution and surface subsidence problem was effectively solved and the load of lift transportation system reduced and the cost of filling technology cut down, which meet the concept of green mining. The industrial experiment verified the safety and stability of the system which can improve enterprises economic benefits and social environmental benefits.

Abstract: When a rock sample is subjected to cyclic loadings, acoustic emission (AE) events increase sharply when the peak stress value applied previously is attained. This phenomenon is called Kaiser effect (KE). One important application of the KE is to determine the in situ stress, the knowledge of which is critical for the design work for underground engineering. Compared to the traditional methods, the acoustic emission (AE) method based on KE is done in the laboratory with special loadings on the rock cores and thus very economical. However, one fundamental question needs to be answered is the influence of the damage introduced by many factors during the period of the coring and samples preparation and so on. In this paper, we explore the influence by a series of loadings on samples in the direction perpendicular to the direction of the previous peak stress. Cyclic uniaxial compressions on the rectangular specimen and cyclic Brazilian tests were carried out based on the contact model in the particle flow code. The results demonstrate that, the disturbance in the orthogonal direction cannot influence Kaiser effect of the rock sample.

Abstract: In order to know the function of downward boreholes and its gas drainage mechanism, gas content field in the goaf is simulated. The changing of gas content of roof tunnel gas drainage and roof tunnel with downward boreholes gas drainage is discussed. The results show that the range in 27m far away from coal face is the gas drainage short area of roof tunnel method, but the downward boreholes cover it. Downward boreholes like a barrier, which prevent gas from flowing to the upper corner in goaf. The gas content in area from coalface to 140m on the upper side of goaf is decreased by roof tunnel with downward boreholes, that reduces the value of gas content over limitation at upper corner. Furthermore, downward boreholes enlarge vertical fracture and realize gas to move to roof tunnel facility. Practical application reveals that the drainage gas is increased by roof tunnel with downward boreholes and gas content in the outlet tunnel is lowed. It is very important to realize high produce safety for gassy coalface.

Abstract: Research on Natural Gas Hydrate（NGH）is very popular in recent years. NGH is a potential, new and clean energy with the characteristics of high energy density, high combustion heat, high proven reserves, no pollution, wide distribution and shallow burial and so on. It has been identified that NGH is widely distributed in the plateau, arctic permafrost and some eligible areas in the seabed of epicontinental and continental slope all around the world. According to the research data on NGH at home and abroad, the mineralizing, formation, distribution and exploration technology of NGH are introduced as well as the NGH research status of countries in the world, including China. Many theories and techniques about the exploitation of NGH are not mature yet. Numerous problems still exist in industrial mining NGH, such as environmental, geological problems induced by mining NGH and storage and transportation problems after mining. Finally, the application and mining prospects of NGH are and prospected and summarized to provide a relatively comprehensive reference to this research field.

Abstract: The control technology for mining subsidence is the main research area of mining subsidence. Its objective is to study and select mining methods appropriate for reducing the surface and overlying strata subsidence and protecting the surface structures. Referring to the analysis of references, the control technology for mining subsidence is discussed from several aspects including backfill mining method, partial mining method, backfill the collapsed cavities in overlying strata, harmonized mining method and 3-step mining method, stripping mining-goaf grouting, and backfill-strip pillar mining. The developing trend of the control technology is also prospected.