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In order to monitor coal face floor water-bearing structure and fissure development in coal mining process and avoid floor water inrush hazard，this paper put forward an encircling face electromagnetic method for monitoring coal face floor water inrush. Through numerical simulation，the study summarized the responses of different position abnormal bodies using encircling face electromagnetic method. The paper presented the design of the encircling face electromagnetic inrush observation system，and put forward the concept of electromagnetic water bursting coefficient. According to the distance between the plate bottom and the water-bearing structure fracture zone，the electromagnetic water inrush coefficient was divided into three level forecast thresholds：water inrush reminding threshold Cr，water inrush warning threshold Cw and water inrush alarming threshold Ca. [ABSTRACT FROM AUTHOR]

In the artificial ground freezing project, the average temperature is the basic parameter for evaluating the frozen soil curtain state and the mechanical analysis of the frozen soil curtain. The average temperature calculation of the frozen soil curtain formed by the single row pipe freezing is studied in this paper. Based on the analytical solution of the steady state temperature field of a single row pipe freezing, the integral calculation of the temperature is directly performed. Using the partial integral method and the integral median theorem, the calculation formula of the average temperature of the single row tube freezing is obtained, and the formula is simplified according to the actual parameter values in the project. Considering that the temperature field analytical solution is not applicable in the frozen pipe area, the same integral strategy is used to solve the influence of the frozen pipe area on the average temperature calculation, and the average temperature calculation formula is corrected. The results of the average temperature calculation formula were compared with the results of the thermal steady state numerical simulation of the single row pipe freezing using ANSYS. The pipe spacing l=0.4, 0.6, 0.8, 1.0, 1.2, 1.4 m, and there are six kinds of frozen development states with relative thickness ξ/l=0.5, 0.6, 0.7, 0.8, 1.0 and 1.5. The values of soil parameters are taken according to the test report and the freezing parameters are commonly used in engineering. The comparison calculation results show that the formula calculation is in good agreement with the numerical calculation results. When the relative thickness is over more than 0.5, the difference between the formula calculation result and the numerical calculation result is rapidly reduced to within 0.5 °C with the development of the frozen soil thickness (relative thickness increase). When the relative thickness is greater than 0.6, the difference between the results is less than 0.2 °C. When the relative thickness is 1 or greater, the difference is less than 0.1 °C. The accuracy of the average temperature calculation formula is verified by numerical simulation, and the rationality of the formula simplification and correction is also explained. The error calculated by the formula satisfies the requirements of engineering application. [ABSTRACT FROM AUTHOR]

To explore the law that rotary wind from drums influences on lateral dissipation of coal dust from cutting, this paper simulated the flowing and dissipation law of wind-coal dust before and after rotary wind from drums into the face, and took the breathing zone as a height range to analyze the coal dust concentration distribution. According to the results of the study and research, a shear scrubber was developed, meanwhile, the application effect was investigated and the results of numerical simulation were verified by the measurement of coal dust concentration. Research indicates that the rotary wind from drums has a strong stability and it has very obvious entrainment to coal dust from cutting, the coal dust from TG drum enter into sidewalk by floor at the leeward 14.2 m of center of shear, the coal dust from MG drum enter into sidewalk by floor at the center of shear, soon afterwards, swarming with wide range at the leeward 2.9 m. At the breathing zone of sidewalk, the peak concentration distribution area is located in the leeward 18.3-21.8 m of center of shear, the coal dust concentration is about 300-400 mg/m3. The relative error of initial measured coal dust concentration compared with the results of numerical simulation is less than 15%. The dust-laying rate of shear scrubber is maintained at 50-80% and its average dust-laying rate is 66.9%. [ABSTRACT FROM AUTHOR]

HJC model has been widely used to describe the dynamic failure process of concrete. However,due to the reason that HJC model contains many parameters, the accurate determination on the parameters of HJC model for rock materials is a challenge. In this paper,the authors performed some laboratory experiments to determine the HJC parameters of sandstone samples that were collected from Weiyuan City,Sichuan,China. Specifically,the authors determined the elasticity modulus,Poisson's ratio,and uniaxial compressive strength of sandstone by uniaxial compression experiments, and the tensile strength by Brazilian disk splitting tests. The strength, strain rate, pressure and damage model constants were determined by fitting the HJC model to the experimental data obtained from the triaxial compression tests and uniaxial SHPB tests. The obtained HJC parameters were used to numerically simulate the SHPB tests of the sandstone samples using finite element program LS-DYNA. The results show that the stress-strain curve predicted by the HJC model is in good agreement with the experimental data. The mean error of dynamic peak stress and corresponding stain obtained by numerical simulation does not exceed 10%. This demonstrates the rationality and validity of the experimental method for determining the HJC parameters. [ABSTRACT FROM AUTHOR]

The co-production of coalbed methane, tight gas and shale gas( “Three gases” ) from one well bore is an effeclive method to improve the productivity of single well and utilization rate of underground resources. However, the gas and water production process under geological conditions, especially the contribution rate from different layers,gas production pressure and gas saturation variation are not clear. In this paper, a numerical model of coalbed methane and light sand gas co-production was established for the first time. Combined with the geological parameters and gas-water output curve of the test well,the factors controlling the gas production were identified. The results show that that the applicability of the co-production model can be compared with single production models,which shows a good suitability; the model can achieve the purpose of production rate classification and the contribution of different layers can be classified; the pressure drop rate decreases, the later of the gas production peak come, however, the production rates in late stages show no much difference; the similar of the sandstone and coal pressure systems, the better of the co-production effect; improving the hydro fracturing results can improve the gas production rate in short term, but show little influence on the accumulated gas production; the effect of shrinkage and stress sensitivity of the coals can significantly improve the gas production effect, however, the physical properties of the coal seam under deep geological conditions need to be further explored. The related results would provide a guidance for the formulation and improvement of drainage systems of coal measure gases and promote “three gases” co-production from one wellbore a step further. [ABSTRACT FROM AUTHOR]

The tunnels often cross joints and faults,which have great influence on tunnel stability during their use.In this paper,these joints and faults were approximated as the cracks through the tunnel.In order to study the influence of the cracks crossing the tunnel on tunnel stability under biaxial pressure,some model tests and numerical simulation were implemented.In the experiment study,Longchang sandstone was used to build tunnel models which were a square plate containing a small “tunnel” and an inclined fault,and in the simulation,Abaqus software was used.Using Abaqus software,the stresses at the points around the tunnel and the stress intensity factor of crack tips were calculated which agreed well with the experimental results.The results show that:① Different angle cracks would have different influence on the stability and strength of tunnel,and produced different stress concentration at the crack tips.When θ is around 40 degrees,the influence of crack on the overall stability and strength of tunnel is maximum,the stress concentration at crack tips is most obvious,KII value is maximum,its shear failure is more serious,and the peak of failure stress is only 41.77% of that of tunnels without cracks.② When θ is around 0 degrees,KII value is close to zero,under vertical pressure the cracks close,the stress concentration of crack tips are not obvious,the cracks are more steady,the failure stress of tunnel is maximum which is 91.23% of that of tunnels without cracks,and this position is the strongest for the tunnel stability.③ Under the influence of vertical stress and confining pressure,the tunnel failure is mainly the pressure-shear failure of the spandrels,side walls,crack tips,and skewbacks,and the tensile failure of arch bottom,vault. [ABSTRACT FROM AUTHOR]

Multiple discontinuities exist in the natural rock mass and these discontinuities are geometrically rough. In this paper, a rough discrete fractures network model ( RDFN) considering the complex and rough geometry distribution of discontinuities is introduced and tested under direct shear test using PFC2D. The corresponding shear behaviors, such as shear strength, shear modulus and failure pattern, were studied and compared with the traditional linear discrete fractures network (DFN) model. Numerical results show that fracture surface roughness can significantly affect the shear behavior of rock masses. The peak strength and shear modulus of the RDFN model are ralatively higher than those of the DFN model. The principal shear fractures in the DFN model mainly coincided along the linear joints. Parts of the intact rock elements were fractured. The failure pattern of RDFN model is much more complex and more intact rock elements were fractured after peak shear strength. The peak shear strength and modulus of all jointed rock models decrease with the increase of sample sizes. The value of shear modulus of the RDFN model is higher than that of the DFN model. The values of shear strength tend to be stabilized with the scale size reaching 4 . 0 m according to the scale effect analysis. [ABSTRACT FROM AUTHOR]

A novel combustion system has been applied to a 600 MW Babcock & Wilcox (B & W) down-fired boiler to reduce NOx emissions without obvious increasing of the carbon content in fly ash.The modification mainly includes rearranging secondary air,and introducing separated over-fire air (SOFA).The aim of this work is to evaluate the overall performance of the novel combustion system with different SOFA ratios (e.g.,15%,20%,and 25%) and different SOFA locations in the upper furnace (e.g.,3.0,4.0,5.0,and 6.0 m above the arches) using numerical simulations.In order to calculate the carbon content of fly ash more accurately,this paper used CBK coke combustion mode.Results showed that not only the NOx emissions were greatly reduced from 823 mg/m3 to 738 mg/m3，but also the carbon content in the fly ash decreased slightly in 0.264% with increasing the SOFA ratio from 15% to 20%.When the SOFA ratio increased from 20% to 25%,NOx emissions only decreased 32 mg/m3,but the combustible content in the fly ash increased obviously in 0.41%.Considering the NOx emissions and combustible content in the fly ash,an SOFA ratio of 20% was advisable.With increasing the height of SOFA from 3.0 to 6.0 m above the arches,the carbon content in the fly ash somewhat increased while NOx emissions decreased.Taking economic efficiency and NOx emissions into account,the location (5.0 m above the arches) was the optimal SOFA location. [ABSTRACT FROM AUTHOR]

In recent years,as the exhaustion of shallow resources and the increase of mining depth,the local slope height reaches 552 m (elevation 142-694 m).Because of the “V” shape of main pit section,the space on the bottom of pit becomes narrow and suffers the risks of rock rolling,landslides and other disasters.These are serious threats to personnel and mechanical safety.To overcome the problems above,Nanfen mine started the new phase of slope expansion and mining.In the last three years,landslide disasters occurred many times during the slope expansion due to the old landslide bodies.This paper uses the “Landslides 2016-1101” case to analyze the in-situ sliding force monitoring and early warning system and establish the landslide causes and failure models.Then,the Stereographic Projection Method is employed in the analysis of landslide mechanism and safety factor.Finally,a numerical modeling analysis by FLAC3D is preformed,particularly involving the Negative Poisson's Ratio cable (NPR) model by Fish language programming.The case of “Landslide 2016-1101” is simulated by numerical calculation,and the result shows a remarkable consistency comparing with the in-situ data.The research may provide a theoretical and practical basis for similar engineering problems. [ABSTRACT FROM AUTHOR]

In view of mine disastrous accidents,once the escape way is blocked,it is hard to locate the miners trapped in the mines.In this paper,the propagation characteristics of electromagnetic wave in coal mine were studied.The finite-difference time-domain (FDTD) method was used to establish the two-dimensional space magnetic field model,which was calculated based on forward simulation technique of GprMax and Matlab software packages.Through theoretical analysis and numerous simulation,the impacts of frequency of antenna center,excitation source,coal types and coal temperatures on the amplitude intensity of the reflected wave and reflection coefficient were investigated.Coupled with the researches referring to the target detection time and resolution,the propagation characteristics of electromagnetic wave in coals were eventually revealed.The results revealed that the Ricker wave with the center frequency of 600 MHz provided the best way of probing.The propagation velocity of electromagnetic wave was the fastest in bituminous coal and lowest in anthracite with lignite in the middle.The propagation velocity of the electromagnetic wave increased with rising coal temperatures.The amplitude intensity of the reflected wave of the human body was weakened with the increase of coal temperature.Further study indicated that the amplitude intensity of the reflected wave of the human body had a logarithmic function with and the detection distance.The above conclusions were then applied for building a database to help the calculation on the thickness of coal between life radar and trapped personnel.The results of this study provide guidelines for the life radar system research as well as the development and on-site rescue detection data interpretation. [ABSTRACT FROM AUTHOR]

The quantitative degree of coal resources exploitation on water environment disturbance is insufficient in the coal mining area of western China. In this paper, it concludes that the spatial scale is the main factor to control the loss of groundwater by the method of groundwater dynamics analysis, which includes the caving zone, the fracture zone, the bending zone and the ground subsidence area. The method of numerical evaluation model of groundwater system is proposed, which is based on the boundary of the hydraulic conductivity of overlying rock, the partition of bending zone, and the re-subdivision of surface subsidence area. According to the quantitative evaluation of groundwater dynamic system disturbance in the Bulianta coal mine, the simulation results show that the loss of groundwater resources is about 1.90×104 m3/d due to the mining disturbance. [ABSTRACT FROM AUTHOR]

Coal-fired heating will greatly save the operating costs in an asphalt mixing plant operating costs.In this paper，we designed swirl combustor burning 4 t/h pulverized coals for the heating system of asphalt mixing plant and numerically studied the combustion characteristic of the swirl chamber was numerically studied. The results revealed that pulverized coal particles were rapidly heated up and stably burnt in the combustor. The distributions of the velocity and temperature fields were rather symmetric. The velocity filed of swirling combustor was determined by the swirl burner and the secondary airs which tangentially shooting into the combustor. When the offset angle between the secondary air and the radial line was greater than 60° and the primary air rate was 0.15-0.20，the flow field in the combustor sounded reasonable，with a combustion efficiency of 97%-99%，the NOx concentration at the exit around 650 mg/Nm3 and excellent load adjustability. Simulation results demonstrated that the swirling pulverized coal combustion is feasible for the asphalt mixing plant and provided some guidance for the combustor design. [ABSTRACT FROM AUTHOR]

In order to study the mechanism of interaction in the process of blended-coal combustion, the experiment and numerical simulation of the influence of out-furnace blending method on the combustion characteristics were performed under bituminous, lean coal and their blended coal (lean coal blends with bituminous of 0,25%, 50%, 75% and 100%) in this paper. The results show that the combustion of blended coal is impacted by two opposite effects: the promote function and the restrain function. The role of the two competition determines the characteristics of blended-coal combustion. The former is that the coal with higher volatile burns firstly, enhancing the local temperature to promote the low-volatile coal ignition. The latter is that the bituminous burns rapidly and consumes much oxygen to make the lean coal in lack of oxygen atmosphere, which hinders the coal combustion and burnout of the lean coal. As increasing the blended bituminous ratio, the temperature rising and O2 consume rates increase,the coal ignition advances, the concentrated combustion region moves forward. Due to the difference of coal quality, interaction effects are obvious, the practical linear-burnout degree is considerably different from the blended coal. When blending 25% bituminous, the promote function plays an important role in the combustion, the burnout degree is higher than the linear-burnout degree. When blending 50% bituminous, the burnout curve presents “turning point”. When further increasing the blending ratio to 75%, the restrain function plays an important role in the combustion, and the burnout degree decreases considerably. NOx emissions of blended coal is in consistence with linear NOx, and increase as the increase of the blending ratios. [ABSTRACT FROM AUTHOR]

The U-steel yieldable support is used in the coal roadway, which is difficult to be supported, due to its characteristics of high retaining ability, contractible capacity and convenient application. However, its own limitations of high cost, poor stability and harsh compressive conditions are difficult to be overcome, which results in its limited application. In order to solve these problems, a grille-yieldable support is proposed, and its internal force characteristic and the mechanical response caused by the yielding under the load are investigated through mechanical calculation, experimental research and numerical simulation analysis in this paper. The results show that this grille-yieldable support has a reasonable structure and a satisfactory performance on bending resistance and torsion resistance. Besides, its stability and bearing capacity are improved to a large extent. During the yielding of the support, the internal force tends to be uniform while the yielding resistance is gradually added. Due to the simplex yielding condition, it is ease to guarantee the support yielding steadily so as to avoid a sudden failure caused by buckling instability. The grille-yieldable support has many advantages such as light weight, low cost, abundant material source and easy manufacturing. In addition, it is convenient to operate with the bolt-shotcrete support, therefore, the grille-yieldable support is a practical roadway supporting form which has a great application prospect. [ABSTRACT FROM AUTHOR]