Journal of China Coal Society, the 1st in the field of mining engineering, promotes the development of coal theory and practice, as well as academic exchanges at home and abroad to accelerate the transformation from scientific research to real productive forces. It is supervised by China Association for Science and Technology and sponsored by China Coal Society. Launched in 1964, it aims at providing key topics of coal scientific research and mining development. Its scope covers coal geology, geochemistry, geophysics, mineralogy and coal seam formation and evolution; petrophysics of coal; organic matter-rich shales, including mineralogy, formation, transport and storage of gases in coal and shales; unconventional energy systems (e.g. oil shales, shale gas, and other carbon-based fuels); ore deposits of materials and rare metals in coal and coal-bearing strata; and groundwater management.
The journal is included in CA, JST, EI, CSCD.
Editor-in-Chief Liu Feng
Associate Editor Fan Baoying, Xu Shengyang, Zhu Shuangcheng
How to evaluate the CBM resources in abandoned coal mines has become a key issue for development. On the basis of study on the deformation and failure law of overlying strata in coal mining, the authors set up an evaluation model and method for evaluating the CBM resources in abandoned coal mines through theoretical analysis and mathematical deduction. In particular, the CBM resources in Jinsheng mine goaf, which belongs to Shanxi Jincheng Anthracite Mining Group Ltd., China, have been evaluated using the evaluation model. Results show that the deformation and failure of the rock mass in coal seam roof, and the stress redistribution of the surrounding rock mass have been caused by coal mining. The CBM resources in abandoned coal mines are mainly composed of adsorbed and free gas from coal pillar, residual coal and surrounding rock. Based on the deformation and failure characteristics of overlying strata and the relationship between porosity and expand coefficient of fractured rock mass, the pore volume models of caving and fracture zones in goaf are established separately. Considering the distribution characteristics of CBM resources and flooded situation in abandoned coal mines, the calculation models of water volume and saturation are also established. Also, the evaluation results show that the abandoned coal mines are abundant of CBM resources, with a coal mine area of 6.5 km2 and a total CBM resource of 5.871 7×108 m3 in coal seam No. 3 of Shanxi Group, Permian. The volume of adsorbed gas is 5.835 3×108 m3 and free gas is 0.036 4×108 m3,and the resource abundance is 0.902 0×108 m3/ km2.
This paper studied the risk evaluation methods of water and sand inrush from coal roof based on the dimensionless multi-factor information fusion technique. Taking Yushenfu coal mine as example, based on the analysis of water and sand inrush mechanism, the paper identified four key factors affecting the water and sand inrush from the roof, which include sand thickness, water richness of aquifer, effective thickness of aquiclude and mining space. Each factor was dealt with dimensionless quantity according to the structural and hydro-geological conditions, and theweights of each factor were determined by entropy weight method, synchronously. Then, the dimensionless multi-factor information fusion model for the risk evaluation Yushenfu coal mine was established on the basis of the ArcGIS. Using the model, the authors got the water and sand inrush risk zoning map in Yushenfu coal mine. The result shows that it is reliable to apply the model on the evaluation and partition of the water and sand inrush from the coal roof in Yushenfu coal mine.
Dynamic failure or even rock burst makes it difficult to keep surrounding rock stay in good control in highintensity mining face. Experimental,theoretical and numerical simulation methods are used in this study to analyzegeotechnical material failure feature and strain energy distribution formation in the surrounding rock under intense min-ing activity and,moreover,mechanism of dynamic failure of the surrounding rock is studied. rock and coal specimensshow static failure formation under low loading rate,but it transits into dynamic failure gradually with increase of theloading rate. Geotechnical material belongs to loading rate dependent material which means the stress state may not besubject to the consistent condition. So the rock and coal may present dynamic failure if the loading rate is too high. With increase of the face advancing rate,loading rate of the major principal stress and unloading rate of the minor prin-cipal distributed in the coal seam are rising which may lead to dynamic catastrophe of the surrounding rock. Strain en-ergy density of the coal near the void space is high and the energy dissipated by the main roof at the fracturing timelead to sudden growth of the strain energy density in the coal which make coal spalling show dynamic features. The dis-tance between positions of the peak point of the strain energy in the coal seam before and after the fracture of the mainroof is the key area of the surrounding rock control.
In order to overcome the problems, such as the emerging support crushing disaster, advance supported deformation and severe destruction of roadway on gob side and some other strong strata behavior problems when the fully-mechanized sublevel caving mining method is applied for mining the Carboniferous No. 3–5 extremely thick coal seam with hard roof in Datong mining area, this study used the methods such as theoretical analysis, physical simulation and field measurement to develop an evolving model for strata structure of mining extremely thick coal seam in large space stope. The result shows that both the key stratum motion at far and near fields in fully-mechanized sublevel caving mining at extremely thick coal seam may exert an influence on strata behavior. The structure model for near field key stratum is "cantilever beam + voussoir beam" broken in the shape of "vertical O-X" while that of far field key stratum is "voussoir beam" broken in the shape of "horizontal O-X". The key stratum structure at near field mainly affects support pressure and its stability on the working face. In the key stratum structure at near field, the more key stratums that move in "cantilever beam", the more harm will be done to the safety of the support. The key stratum structure at far field mainly exerts an influence on the deformation of roadway on gob side of the working face. The rotary motion of thebroken block will produce radial extrusion on wall rock in roadway on gob side, which is the main reason for the floor heave of roadway. Accordingly, the hard roof control technology, based on the far and near field synergetically weaken which combines ground drilling fracturing with underground presplitting roof, is developed. This technology will effectively reduce the pressure transmission from the energy release of rock breaking to the structural instability of key stratum and mitigate the mine pressure intensity of fully-mechanized sublevel caving mining stope for mining the extremely thick coal seam.
The coal mining height measurement problem has been addressed and a solution method has been proposed using hydraulic support angle sensor. The measurement height model was analyzed by using a two-leg type hydraulic support's angle. Then, considering the base of slope angle, the influence of inclined slope angle formula was derived for height measurement. To analyze the factors influencing the precision of height measurement,the authors examined the procedure with the aim of improving the accuracy of angle measurement including changing the installation posi-tion, and using the Kalman filtering method to eliminate vibration noise. A height measurement system with four dual-axis tilt sensors was designed using angle measurement method. The height measuring sensor method was verified by performing ground tests in the laboratory and underground experiments. A height measurement accuracy of 5–10 cm in 6 m hydraulic support has been achieved. In comparison with the laser ranging, the test results have shown that the proposed method has a stronger environment adaptability in coal dust environment.
Coal burning emission is one of the major sources of the airborne particulates in northern China. In this paper, the trace elements in inhalable particulates (PM10) collected from a combustion-dilution system by burning different coals in laboratory were studied by the ICP-MS (Inductively coupled plasma mass spectrometry). The raw coals were collected from the coal mines in five different regions, namely Zhijin, Datong, Dongsheng, Yinchuan and Jingxi. The results indicated that the major elements Zn, Fe, Rb, Pb, Cu, Cr, Ti, Mn, Ba, Ni, and As were enriched, in a descending order, in the whole sample of PM10 derived from burning coal. The water-soluble trace elements in PM10were mainly Zn, Rb, Pb, Cu, Ti, As, Ni in a descending order of contents. The percentage of the water-soluble Cs, Rb, Cd, Tl, Sb, and Zn over the total individual trace element was relatively high. This indicated that these elements existed mostly in water-soluble state in PM10 derived from burning coal. Interestingly, Fe was not detected in the water-soluble fraction of PM10, indicating that Fe existed mainly as insoluble state in coal burning PM10. The rare earth elements in PM10 emitted from burning coal were dominated by Sc, Ce, Nd and La. The contents of the total analyzed trace elements (TATE) were the highest in the PM10 emitted from burning the Yinchuan Coal, followed by the PM10s from burning the Zhijin, Jingxi, Datong, and Dongsheng coals in a descending order. The higher levels of the TATE in PM10 emitted from burning the Yinchuan and Jingxi coals were due to the high ash contents in the raw coals, and the higher levels of TATE in the PM10 emitted from burning the Zhijin Coal were attributed to the high sulfur content in the raw coal.
In order to solve the problem that the classical diffusion model cannot accurately fit a full-time gas diffusion process in coal particle, the experiments of gas diffusion in coal particle were carried out under various conditions using typical coals in China. The results calculated by classical diffusion model show that the experimental values of diffusion ratio are greater than the theoretical value before a certain time, however, the former is less than the latter after that time. The classical diffusion model cannot precisely fit a full-time gas diffusion process and the error is large, and then the special phenomenon for diffusion coefficient decrease with the increase of time was found. The new physical modelof multi-scale pore distribution in coal was put forward. Based on new model, the authors assumed that the pore distribution within coal is heterogeneous and multi-scale, and has self-similar fractal structure, which causes the multi stage distribution of diffusion coefficient within coal and determines the macroscopic diffusion mechanism of gas. From the surface to the center of coal, the pore distributes from big to small and the diffusion coefficient decreases accordingly. Gas diffuses rapidly from the big pore with large diffusion coefficient in the early stage and slowly from the small pore with small diffusion coefficient in the late stage until the micro pore is finally influenced. The multilevel diffusion coefficient distribution caused by multi-size pore results in the diffusion mechanism of diffusion coefficient decease with the increase of time. According to the assumption, two parameters, initial diffusion coefficient(D0) and decay coefficient(β), were introduced to reflect the decay characteristic of dynamic diffusion coefficient. The mathematic model of dynamic diffusion coefficient was put forward. The new model, verified by 200 data, can fit the full-time process of gas diffusion in coal under various conditions. Meanwhile, the new model covers the classical unipore diffusion model and bidisperse one and generalizes the latter ones. The new model can explain the problems caused by classical one, and interms of accuracy, simplicity, explanatory and predictability, the new model is better than the bidisperse model and empirical equations. The new model provides a new algorithm to determine coalbed methane content, reserves and outburst predicting index and to explain the diffusion mechanism under various conditions.
To study the mechanics and permeability characteristics of similar material of solid-gas coupling, orthogonaltest is used to make up similar material which using river sand as aggregate, paraffin as cementing agent and hydraulicoil as regulator. Adopting range analysis and multivariate regression analysis, the influence of impact number, aggregatesize, oil content and cement-sand ratio on the compressive strength, elasticity modulus, Poisson's ratio and permeabili-ty of similar material are investigated. The test results show that the size order that factors against compressive strengthis oil content, impact number, aggregate size, and cement-sand ratio. The size order that factors against elasticity modu-lus is oil content, impact number, cement-sand ratio and aggregate size. The size order against permeability is impactnumber, cement-sand ratio, oil content and aggregate size. The factors have less influence on Poisson's ratio. The com-pressive strength and elasticity modulus of similar material is positively related to impact number and aggregate size, and is negatively related to oil content and cement-sand ratio. The permeability is negatively related to impact number, aggregate size, oil content, and is positively related to cement-sand ratio. Poisson' s ratio has no obvious relationshipwith the factors. The comprehensive model of characteristic parameters of similar material is obtained under the influ-ence of four factors in test.
