Study of electromagnetic characteristics of stress distribution and sudden changes in the mining of gob-surrounded coal face

The incidence of dynamic coal or rock disasters is closely related to the distribution of stress in the surrounding rock. Our experiments show that electromagnetic radiation (EMR) signals are related to the state of stress of a coal body. The higher the stress, the more intense the deformation and fractures of a coal body and the stronger the EMR signals. EMR signals reflect the degrees of concentrated stress of a coal body and danger of a rock burst. We selected EMR intensity as the test index of the No.237 gob-surrounded coal face in the Nanshan coal mine. We tested the EMR characteristics of the stress distribution on the strike, on the incline and in the interior of the coal body. The EMR rule of rock bursts, caused by sudden changes in stress, is analyzed. Our research shows that EMR technology can be not only used to test qualitatively the stress distribution of the surrounding rock, but also to predict a possible occurrence of rock burst. Based on this, effective distress measures are used to eliminate or at least weaken the incidence of rock bursts. We hope that safety in coalmines will be enhanced.

Research on inversion high mining pressure distribution and technology of preventing dynamic disasters by MS monitoring in longwall face

Under two rock strata combination conditions,over 10,000 microseismic eventswere received with microseismic location monitoring technology which possessed by theauthor's studying team,used in fully mechanized coal face of Huafeng Mine of XinwenCoal Mining Group Co.,Shandong Province.On the basis of the achievement of the locationresults,the conclusions were drawn as follows:On the basis of the achievement of 3Dstrata fracturing situation and the section plane of microseimic events in different areas,the relationship between spatial structure of overlying strata and mining pressure field wasfound,and we might describe distribution range of dynamic pressure of advance pressureand lateral stress around long face,and range of structure ad-tivation.Quantitative guidanceto prevent dynamic disasters was provided.The practice in coal mine got a effectiveresults.According to the FLAC3D soft numerical simulation of diameter drilling hole (thediameter is 300 mm) to relieve pressure in specified geological condition in Huafeng Mine,the right distance of two dirlls is 2.5 m and the right depth is 12 m.The research pro-videdbasic guiding and practical experiences for the underground microseismic monitoring anddisaster prevention in side slopes or tunnels engineering.

Evaluation and empirical research on the energy efficiency of 20 mining cities in Eastern and Central China

The gap of energy efficiency of eastern and central mining cities in China continues to expand, getting more attention from relevant departments. In this work, 20 mining cities in Eastern and Central China from 2010 to 2014 have been selected as research samples using data envelopment analysis(DEA).Research results show that the level of energy efficiency in mining cities is still low. China is in an extensive economic growth mode with high input, high consumption, low output and low efficiency. Mining cities in China have a huge potential to conserve energy and reduce emissions. China should optimize industrial structures, strengthen scientific and technological input and innovation, as well as implement energy-saving emissions reductions, and increase investment in environmental protection and ideological propaganda.

Assessment of gas and dust explosion in coal mines by means of fuzzy fault tree analysis

During the past decade, coal dust and gas explosions have been the most two serious types of disasters in China, threatening the lives of miners and causing significant losses in terms of national property. In this paper, an evaluation model of coal dust and gas explosions was constructed based on a fuzzy fault tree by taking the Xingli Coal Mine as a research site to identify the risk factors of coal dust and gas explosions.Furthermore, the hazards associated with such explosions were evaluated for this particular coal mine.After completing an on-site investigation, the fuzzy probabilities of basic events were obtained through expert scoring, and these expert opinions were then aggregated as trapezoidal fuzzy numbers to calculate the degrees of importance of all basic events. Finally, these degrees of importance were sorted. According to the resulting order, the basic events with higher probabilities were determined to identify key hazards in the daily safety management of this particular coal mine. Moreover, effective measures for preventing gas and coal dust explosions were derived. The fuzzy fault tree analysis method is of high significance in the analysis of accidental coal mine explosions and provides theoretical guidance for improving the efficiency of coal mine safety management in a scientific and feasible manner.

Surrounding rock control of gob-side entry driving with narrow coal pillar and roadway side sealing technology in Yangliu Coal Mine

Gob-side entry driving can increase coal recovery ratio, and it is implied in many coal mines. Based on geological condition of 10416 working face tailentry in Yangliu Coal Mine, the surrounding rock deformation characteristics of gob-side entry driving with narrow coal pillar is analysed, reasonable size of coal pillar and reasonable roadway excavation time after mining are achieved. Surrounding rock control technology and effective roadway side sealing technology are proposed and are taken into field practice. The results showed that a safer and more efficient mining of working face can be achieved. In addition, results of this paper also have important theoretical significance and valuable reference for surrounding rock control technology of gob-side entry driving with narrow coal pillar under special geological condition.

Practice of Fighting Fire and Suppressing Explosion for a Super-Large and Highly Gassy Mine

The Baijigou Mine fire in Ningxia Province,which broke out on October 24,2003,affected more than 108 m3 of the mine and was probably the largest underground fire in China in recent years. In addition to its size,the fire was also characterized by excessive air leakage and the potential for violent methane explosions. A series of new measures were taken to fight the fire,including sealing intake tunnels with water,injecting three-phase foam through boreholes,and flushing with a large volume of nitrogen. The fire was successfully extinguished and production re-sumed soon afterwards; not one single methane explosion occurred during fire-fighting and afterwards.

Study of 3-D Numerical Simulation for Gas Transfer in the Goaf of the Coal Mining

In order to simulate field distribution rules,mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established,based on theories of permeability and dynamic dispersion through porous media. A gas dispersion equation in a 3-D field is calculated by use of numerical method on a weighted upstream multi-element balance. Based on data of an example with a U type ventilation mode,surface charts of air pressure distribution and gas concentration are drawn by Graphtool software. Finally,a comparison between actually measured results in the model test and the numerical simulation results is made to proves the numerical implementation feasible.

Experimental research into the effect of gas pressure,particle size and nozzle area on initial gas-release energy during gas desorption

Coal and gas outburst is a violent disaster driven by released energy from gas desorption.The initial expansion energy of released gas(IEERG)is a new method to predict coal and gas outburst.In this paper,an instrument for IEERG measurement was developed.Compared with previous setups,the new one which is equipped with three convergent nozzles and quick-release mechanism gets improved in data acquisition and gas sealing and releasing performance.To comprehensively know the effect of gas pressure,particle size,and nozzle area on IEERG,a series of experiments were carried out with this new setup.The variable control test results indicated that the gas pressure-IEERG curves remain the linear trend and the particle size-IEERG curves maintain the negative exponential trend for nozzle areas at 1.13,2.26,and3.39 mm2,respectively.The increase in nozzle area leads to deceases in value of IEERG and absolute value of slope of fitting curves in each test.In addition,the orthogonal experiment showed that the influence of gas pressure,nozzle area,and particle size on IEERG decreases in turn.Only gas pressure had a marked impact on IEERG.This work offers great importance in improving the accuracy of prediction of coal and gas outburst.

Research into stope roof control of compound roof by solid backfilling mining

Based on the analysis of the failure characteristics and backfilling effect of the compound roof at 1801 backfilling workface in Taiyuan coal mine,China,we propose a method of controlling the presubsidence of a compound roof by using pre-stressed bolts to improve the backfilling ratio of the workface so as to maintain the global stability of the stope roof.In addition,PHASE simulation software was employed to analyze the influence law of pre-stressing force,length,and interval on roof subsidence at the workface.On the basis of the numerical simulation results,a model for calculating the pre-stressing force and length of the bolts,the interval between the bolts,as well as roof subsidence at the workface,was established by using SPSS regression analysis software.Moreover,the research results were applied successfully to the 1801 filling workface.According to the monitoring data of roof closure,it was found that the final subsidence value for the goaf roof was 350 mm and the filling ratio at the workface was 86%,which could fully meet the demand for safety production at the workface.The safe and effective control of the stope roof was therefore realized,which achieves the goal of safe and efficient backfilling mining under a compound roof.

Similar simulation device for unloading effect of deep roadway excavation and its application

The unloading effect of the excavation of deep roadways has been considerably studied, but most research methods have been limited to numerical simulations and field measurements. Only a few have adopted experimental methods for similar simulations. On the basis of the theory of mechanics,the testing system is designed considering initial geostress and dynamic unloading. The system includes an impact unloading gear and in-situ stress loading equipment, and a designed three-link structure and the impact hammer can effectively realize the dynamic excavation of roadways.Meanwhile, a cyclic excavation similar simulation experiment on a deep roadway is conducted in a laboratory. The testing system and the relevant monitoring facilities are utilized, and the unloading effect inside the surrounding rock under the cyclic dynamic excavation is studied. Results show that the cyclic dynamic excavation causes significant unloading only in the nearby rock mass, and the unloading indicators show nonlinear changes.Moreover, when the lateral pressure coefficient is 1.2,the damage is concentrated on both roadsides due to the excavation unloading. Meanwhile, the damage gradually decays as the span increases.

Similar material simulation research on movement law of roof over-lying strata in stope of fully mechanized caving face with large mining height

Similar material simulation test was carried out in a geological model ofW_(9-15)101 fully mechanized caving face with large mining height in the Liuhuanggou Colliery,in Xinjiang Uigur Autonomous Region.The roof overlying strata movement law in thestope of a fully mechanized caving face with large mining height was studied and showthat the roof overlying strata in the stope of a fully mechanized caving face with large miningheight can be formed into a stable arch structure; the fracture rock beam is formed resemblinga 'bond beam', but it has essentially the structure of 'multi-span beams' underthe big structure of the stable arch.The roof overlying strata movement law in the stope ofa fully mechanized caving face with large mining height is similar to that of the common,fully mechanized caving stope, which is determined by the deformation and instability ofthe structure of 'multi-span beams'.But because of the differences between the miningheights, the peak pressure in the stope of a fully mechanized caving face with large miningheight is smaller while the affected area of abutment pressure is wider in the front of theworking face; this is the obvious difference in abutment pressure between the stope of afully mechanized caving face with large mining height and that of the common.

Aeroelastic dynamics stability of rotating sandwich annular plate with viscoelastic core layer

A dynamic model for a rotating sandwich annular plate with a viscoelastic core layer is developed. All fundamental equations and boundary conditions are estab- lished based on Hamilton＇s principle, and the rotation effect and viscoelastic properties of the sandwich structure are taken into account. The aerodynaxnics force acting on the plate is described by a rotating damping model, and the constitutive behavior of the viscoelastic core layer is formulated by the frequency-dependent complex modulus. The effects of geometrical and material parameters on frequencies and damping of forward and backward traveling waves and the dynamic stability for the rotating sandwich plate axe numerically analyzed by means of Galerkin＇s method. The results show that the critical and flutter speeds of the rotating plate can he increased at some certain parameters of the viscoelastic core layer.

Stability control of surrounding rocks for a coal roadway in a deep tectonic region

In order to effectively control the deformation and failure of surrounding rocks in a coal roadway in a deep tectonic region, the deformation and failure mechanism and stability control mechanism were studied. With such methods as numerical simulation and field testing, the distribution law of the displacement, stress and plastic zone in the surrounding rocks was analyzed. The deformation and failure mechanisms of coal roadways in deep tectonic areas were revealed: under high tectonic stress, two sides will slide along the roof or floor; while the plastic zone of the two sides will extend along the roof or floor,leading to more serious deformation and failure in the corner of two sides and the bolt supporting the corners is readily cut off by the shear force or tension force. Aimed at controlling the large slippage deformation of the two sides, serious deformation and failure in the corners of the two sides and massive bolt breakage, a ‘‘controlling and yielding coupling support'' control technology is proposed. Firstly, bolts which do not pass through the bedding plane should be used in the corners of the roadway, allowing the two sides to have some degree of sliding to achieve the purpose of ‘‘yielding'' support, and which avoid breakage of the bolts in the corner. After yielding support, bolts in the corner of the roadway and which pass through the bedding plane should be used to control the deformation and failure of the coal in the corner. ‘‘Controlling and yielding coupling support'' technology has been successfully applied in engineering practice, and the stability of deep coal roadway has been greatly improved.

Dust removal efficiency of high pressure atomization in underground coal mine

To master theoretical calculation for dust removal efficiency of high pressure atomization in an underground coal mine, the corresponding atomization characteristics and dust removal efficiency were both comprehensively studied in theory by virtue of related theories of hydromechanics and aerosol.According to actual measurements of flow coefficients and atomization angles of X-type swirl nozzle,computational formula was derived for atomized particle sizes of such a nozzle in conjunction with relevant empirical equation. Moreover, a mathematical model for applying high pressure atomization to dust removal in underground coal mine was also established to deduce theoretical computation formula of fractional efficiency. Then, Matlab was adopted to portray the relation curve between fractional efficiency and influence factors. In addition, a theoretical formula was also set up for removal efficiency of respirable dust and total coal dust based on dust size and frequency distribution equations. In the end,impacts of dust characteristic parameters on various dust removal efficiencies were analyzed.

Molecular Phylogeny Supports the Validity of Polypedates impresus Yang 2008

The taxonomy of the Asian tree frogs of the Polypedates leucomystax complex, a group of widespread and morphologically similar species, is very controversial. To ascertain the taxonomic status of these species, we investi- gated the historical relationships among representative samples based on - 2 kb of nucleotide sequences from the mito- chondrial 12S rRNA, tRNAvalinc, and 16S rRNA genes. Our phylogeny resolved five well supported lineages （A, B, C, D and E） in the P leucomystax complex. Polypedates impresus from Yunnan, China, Polypedates cf. mutus and Polypedates cf. megacephalus from Guangxi and Yunnan, China, and Laos constructed Clade C, which is monophyletic. In order to recognize the unique position of this clade, we considered P impresus in Clade C as a valid species. Following our phy- logeny, Chinese Polypedates, corresponding to the other four clades, should include four species： P. mutus （Clade A）; P. braueri （Clade B）; P impresus （Clade C） and P. megacephalus （Clade D）. P Ieucomystax （Clade E） is mainly distributed in the Malaysia, Indonesia and Philippines.

Calculation of Apparent Activation Energy of Coal Oxidation at Low Temperatures by Measuring CO Yield

By analyzing previous studies on activation energy of coal oxidation at low temperatures, a theoretical cal- culation model of apparent activation energy is established. Yield of CO is measured by using the characteristic detector of coal oxidation at 30–90 ℃ . The impact of parameters, such as airflow and particle size, on activation energies is ana- lyzed. Finally, agreement was obtained between activation energies and the dynamic oxygen absorbed in order to test the accuracy of the model. The results show that: 1) a positive exponential relation between concentration of CO and temperature in the process of the experiment is obtained: increases are almost identical and the initial CO is low; 2) the apparent activation energies increase gradually with the sizes of particle at the same airflow, but the gradients increase at a decreasing rate; 3) the apparent activation energies increase linearly with airflow. For the five coal particles, the differences among the energies are relatively high when the airflow was low, but the differences were low when the air- flow was high; 4) the optimum sizes of particle, 0.125–0.25 mm, and the optimum volume of airflow, 100 mL/min, are determined from the model; 5) the apparent activation energies decrease with an increase in oxygen absorbed. A nega- tive exponential relation between the two is obtained.

Research on new type of numerical method for material creep analysis

Based on the principles of virtual work for continuum medium,the element free Galerkin method to simulate the numerical calculations of steady-state creep was used and the discrete equation was derived in meshlss method for steady-state creep.The es- sential boundary conditions and volume incompressible conditions can be realized by em- ploying the penalty parameters,so the symmetric positive definite system stiffness matrix can be yielded.Results of numerical cases show that element free Galerkin method,with its high accuracy,is much more convenient to deal with the pre-process and post-process, the results by meshless method is in good agreement with the exact solution data.