Applied Mechanics and Materials Vols. 448-453

Abstract: High purity phosphatic chemicals should be produced for the development of phosphorus chemical industry. The effects of pairwise combination of scrubbing, calcination and flotation techniques on chemical composition content of different size fractions of a siliceous-calcareous phosphate ore are investigated. The grades of the different size fractions processed by flotation first and then by calcination are higher than those processed by scrubbing first and then by calcination. The grades of the coarse fractions are all higher than 30%, and it can be up to 35.43% for the 98~200 μm fraction. Moreover, the A.I. contents of the all fractions decrease obviously. Especially, it decreases from 11.12% to 5.14% for the fine < 74 μm fraction, which is lower than that processed by scrubbing first and then by calcination about 5%. The SEM images indicate that the effects of scrubbing and calcination on surface characteristics of ore samples are different.

Abstract: Flotation behavior of pure quartz is difference from that of the quartz gangue of a siliceous-calcareous phosphate ore with fine size. The flotation of pure quartz can attain satisfactory results at alkaline conditions. The IR analysis shows that adsorption intensity of quaternary ammonium salt is stronger which is likely to explain its preferable flotation performance for pure quartz. However, for quartz gangue of phosphate ore, the results are completely opposite. The acid condition is more favorable for reverse flotation than alkaline condition due to the existence of carbonate mineral. The alkyl amine salt is a more effective collector to remove quartz gangue from siliceous-calcareous phosphate ore, especial with 12 carbon chain. Zeta potential of the ore treated by it is almost higher than that by the other alkyl amine salts (with 10, 14 or 18 carbon chain), which suggests its stronger absorption on ore particles.

Abstract: To prevent threaten of impact disaster, high-pressure water is injected into coal face, which is most widely used in impact-type mine. In such cases, by analyzing the rock burst tendency of a particular type of deep mining pit and occurrence of the mining process, rock samples drilled from the coal mine were taken for the conventional mechanical properties test and rock burst tendency test respectively under dry and wet state. Cuttings volume indicator affected by injection has been optimized to improve the prediction sensitivity. "One shift anti-impact, two-shift production "patterns labor organization model, adjusted development system layout and cut drilling index optimizations, as well as the allocation of high-pressure water injection drilling means, greatly improving the water injection effect, which probably provide a reference for similar mines to safe and efficiently mining.

Abstract: In China, surface subsidence caused by steep coal seam mining has affected the safe operation of pipelines in recent years. The study site is one coal mine, where the gas pipeline from Shanshan to Urumqi is across. FLAC^3D was adopted to study subsidence-induced stress on the pipeline, and the numerical model was calibrated with the measurement data. Visualization of alarm levels on the pipeline was obtained by integrating the usage of Fish function embedded in FLAC^3D and Tecplot. The simulations reveal that the stress on the pipeline is closely related to the excavation depth. The stress on the pipeline increases with the excavation depth increasing when mining the 1st, 2nd, and 3rd levels, whereas the stress on the pipeline decreases slightly with the excavation depth increasing when mining the fourth, fifth, and sixth levels. The maximum stress on the pipeline occurs after mining the 3rd level. The possible damage to the pipe is at the upper-right side. Therefore, the results are helpful to prevent and reduce the impact of subsidence on the pipeline.

Abstract: Subjected to external forces, the structure surface between rocks (ie, bedding planes) should be deformed under external force. If the two side walls of the rock bedding plane has perfectly flat smooth surface, after the composite layered rock subjected to force, bedding plane can be closed as surface contact manner. However, the rock bedding plane side walls generally showed local contact state in the nature, the rock layers of bedding planes will produce compressive deformation under stress. Through complete stress - strain triaxial loading experimental study on the effects of the presence of horizontal bedding on layered composite rock strength and deformation, and the elastic deformation of layered rocks are calculated using elastic mechanics, the result shows that due to the presence of irregular bedding plane, the presence of horizontal bedding formation will reduce the overall strength, and increase the overall rock deformation.

Abstract: Aim at the phenomenon of sidestep subsidence on surface by mining on the condition of thick unconsolidated layers and thin stratum,article bases on the theory analysis and calculation, and uses determining key strata and key strata flexibility calculation, and expatiates the characters of η, and makes it divide into subsection function. Contrast with project example and simulation test, it shows:if subsection function η is applied, then using it to forecast the quantity of surface subsidence that will be more approach to fact, which can syllabify explain phenomenon of sidestep subsidence on surface, and has definite meaning to coach locale.

Abstract: A coal mine in Chongqing +590m south four district 2443 working face as the research object, using the finite difference method (FLAC) which can solve the nonlinear large deformation problem, setting up the mechanical analysis model of the gob-side entry retaining, analyzing the structure characteristics of surrounding rock, and studying on the stability of surrounding rock of the gob-side entry retaining under the mining. the results showed that:(1) After the coal mining, the maximum displacement of roof has occurred on the edge of the roadway upper side near the filling body. The floor heave at the beginning mining, the floor has a downward displacement after the mining;(2)After the coal mining, the surrounding rock of the gob-side entry retaining has a larger range of shear failure, a strong tensile damage was occurred in filling body, big horizontal displacement was happened in the middle of filling body. Research results can provide reference for similar coal mining..

Abstract: The process of fractures developing of coal and rock and overlying strata movement is a temporal dynamic evolution process. In this paper, based on the research object a working face of a mine, using the UDEC numerical simulation software to research the movement of the working face upper strata in mining process, the results showed that the overlying strata forms "vertical three zones" in the vertical direction from bottom to top. Overlying strata above the goaf displays a fracture table with a trapezoid shape entirely; the cut side of the fracture angle is slightly larger than the working face side of the fracture angle. Numerical simulation calculation of the height of two zones will get a close consistent result to empirical formula. The conclusions have important guiding significance for reasonable arrangement of the gas exploitation.

Abstract: Use Taiping coal mines second horizontal (+1100m~+900 m level ) 1#, 3# and 5# coal seam in Panzhihua Baoding as the research object, apply the problem solving nonlinear large deformation finite difference method (FLAC), to research the steep multi-seam mining of pressure distribution and characteristics of fracture zone. The results show that: (1)During the course of three coal mining extraction, the stress of goaf surrounding rocks will be changed. (2)When the nearby coal is mining, the coal pillar come into being stress concentration near the area. when the mining work continues, the goaf will have an effect on the protection pillar, which is similar to the "liberate". the effect of coal pillar and stress concentration nearby will be eased; (3)After the coal mining, plastic failure has occurred over the protection pillar, forming a water guide channel. Research results can be as a reference for similar steep seam mining.

Abstract: Surrounding rock constantly changes in the process of the stress concentration and release alternately with the method of caving mining, coal and surrounding rock break and form some channels for gas migration, causing the gas permeability o f surrounding rock changes. As the research object of coal mine in Shanxi with caving mining method, using the exponent relation of permeability and stress change, establishing the concept of relative permeability, based on FLAC^3D software, revealing the law of rock permeability variation in the mining process. The study shows: (1) the relative permeability can directly characterize the level of rock (coal) affected by mining; (2) in the vertical direction, the roof and floor have a wide range of relief, permeability increases and then decreases exponentially, affecting the range 30 ~ 40m; (3) overburden above the mined-out area damaged as an "O"-ring; (4) immediate roof obvious with a relief range of about 45 ~ 60m. Therefore the study has good guidance on gas drainage.