Present situation of fully mechanized mining technology for steeply inclined coal seams in China
中国大倾角煤层综采技术现状
Arabian Journal of Geosciences, August 2014
Abstract: Abundant and widely distributed in China, steeply inclined coal seams generally have diverse and complicated geological characteristics. Intrinsic problems in mining such seams, such as large dip angle, short length of mining face, ineffective sealing and protection of working space by support systems, poor stability of equipment, high labor intensity, and inadequate protection of the workers hinder the safe and efficient excavation. Recently, significant progress has been made in China in mining such coal seams. In some coal mines, fully mechanized mining technology has been successfully applied, and working face outputs were increased remarkably. This paper analyzes the main technical difficulties in applying fully mechanized mining technology, such as surrounding rock control, mining equipment stability control, skidding prevention, and flying gangue prevention. Based on the analysis, prosperous development directions for steeply inclined coal seam mining in China are proposed.
Discontinuous Modelling of Stratum Cave-in in a Longwall Coal Mine in the Arctic Area
寒带区长臂开采煤矿岩层陷落非连续模拟
Geotechnical and Geological Engineering, October 2014, Volume 32, Issue 5, pp 1239-1252
Abstract: This paper presents a discontinuous numerical approach for studying roof cave-in mechanisms and obtaining the required support capacity of longwall shields in a case study site, the Svea Nord coal mine in Svalbard. The block size in the roof strata and the mechanical parameters of the discontinuities for the numerical model were obtained through back-calculations. The back-calculations were conducted with a statistical method of design of experiment. Numerical simulations revealed that voussoir jointed beams are formed before the first cave-in occurs. The maximum deflection of a roof stratum in the study site prior to the first cave-in is about 70 % of the stratum thickness. The maximum span of the roof strata prior to the first cave-in depends upon the in situ horizontal stress state. The roof beams have a large stable span when they are subjected to high horizontal stress; but horizontal stress would increase the possibility of rock crushing in deflected roof beams. The simulations and field measurements show no periodic weighting on the longwall shields in the study site. Stiff and strong roof beams would result in large first and periodic cave-in distances. As a consequence of having large cave-in distances, the longwall shields must have high load capacity, which can be calculated by the presented numerical approach.
Interactions of overburden failure zones due to multiple-seam mining using longwall caving
长臂放顶多层开采引起的覆岩破坏区域的相互影响
Bulletin of Engineering Geology and the Environment, September 2014
Abstract: This paper presents an investigation on the interactions of overburden failure zones induced by the mining of adjacent coal seams using the longwall caving method. Overburden failure is an important factor in safety assessments in the fields of mining engineering geology and safety geology, especially when mining under water bodies. In this study, the influence of the thickness and properties of the interburden between seams on the development and interactions of caving and fractured water flow zones are investigated by using in situ measurements, scale model testing and numerical simulations. The height of the fractured water flow zones in the scale model tests and numerical simulations are basically in good agreement with measurements after mining of the upper and lower seams of Seam No. 3 in the Cuizhuang Coalmine. Therefore, the scale tests and numerical simulations in the study are verified. The results show that interaction and superposition between two close distance seams cannot be ignored when the ratio (h/M) of the interburden thickness (h) to the cutting height of the lower seam (M) is less than a defined critical value. A dividing line, Line D, has been proposed to judge whether the interactions exist. When the (M, h/M) points are located above Line D, the caving zone induced by excavation of the lower seam will not propagate to the caving zone induced by the upper seam. Otherwise, for the (M, h/M) points below Line D, the interactions and superposition of the overburden failure must be considered when predicting the heights of the caving and fractured water flow zones
Selection of overburden surface mining method in West Virginia by analytical hierarchy process
在西弗吉尼亚通过层次分析法选择剥离开采法之实践
International Journal of Coal Science & Technology, September 2014
Abstract: The broad objective of this research was to improve current surface mining practices and reduce negative environmental impact of overburden removal in West Virginia (WV). The specific objectives were to (i) compare conventional surface mining method (drilling, blasting, digging, and loading) to a surface miner (SM) method, and (ii) apply the analytical hierarchy process (AHP) to help select the optimal mining method based on production, cost and environmental criteria. The design and the procedures used in this research involve five interrelated modules: (i) rock properties of overburden in WV, (ii) drilling and blasting, (iii) digging and loading, (iv) SM method, and (v) comparative analysis and selection of the optimal mining method by AHP. Results of this research indicate that application of SM method would yield higher cost of overburden removal than conventional mining methods in rocks with a high unconfined compressive strength and abrasivity. A significant advantage of SM method, where applicable, is the elimination of the negative environmental impacts associated with blasting.
An EMR-based method for evaluating the effect of water jet cutting on pressure relief
基于EMR的水射流切割对卸压影响的评估方法
Arabian Journal of Geosciences, August 2014
Abstract: Water jet cutting (WJC) can play a good role in coal pressure relief. Its effect is commonly evaluated using a traditional method based on debris-drilling amount. However, this evaluating result is unsatisfactory due to great artificial interference. Based on previous experimental researches on the relationship of electromagnetic radiation (EMR) to stress during the failure of coal rock under loading, we analyze the EMR response to seam pressure relief using WJC from the angle of stress relief and carried out experiments to verify that EMR response could be used to evaluate the effect of WJC on coalbed pressure relief at Xinzhi and Yuejin Coal Mines, China, with self-developed KBD5 EMR monitor. The research showed that after WJC, the intensity and changes of EMR reflect not only the stress level from which the cut coal seam suffered but also the processes of stress transfer and evolution, thus proving that EMR can be used to evaluate the effect of WJC for coal mass pressure relief. Moreover, the experiments also showed that if without borehole collapse after WJC, multiple WJC in the same borehole can be performed to monitor EMR signals and when two adjacent signal curves keep at the same level and without obvious decline, WJC could fully release pressure in coal mass.
Orthogonal design and numerical simulation of room and pillar configurations in fractured stopes
破坏采场房柱布局的正交设计与数值模拟
Journal of Central South University, August 2014, Volume 21, Issue 8, pp 3338-3344
Abstract: Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3D. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.
Prediction of global stability in room and pillar coal mines
房柱式煤矿全局稳定性预测
Natural Hazards, June 2014, Volume 72, Issue 2, pp 405-422
Abstract: Global stability is a necessary prerequisite for safe retreat mining and one of the crucial and complex problems in room and pillar mining, so its prediction plays an important role in the safety of retreat mining and the reduction of pillar failure risk. In this study, we have tried to develop predictive models for anticipating global stability. For this purpose, two of the most popular techniques, logistic regression analysis and fuzzy logic, were taken into account and a predictive model was constructed based on each. For training and testing of these models, a database including 80 retreat mining case histories from 18 room and pillar coal mines, located in West Virginia State, USA, was used. The models predict global stability based on the major contributing parameters of pillar stability. It was found that both models can be used to predict the global stability, but the comparison of two models, in terms of statistical performance indices, shows that the fuzzy logic model provides better results than the logistic regression. These models can be applied to identify the susceptibility of pillar failure in panels of coal mines, and this may help to reduce the casualties resulting from pillar instability. Finally, the sensitivity analysis was performed on database to determine the most important parameters on global stability. The results revealed that the pillar width is the most important parameter, whereas the depth of cover is the least important one.
Coal and gas outburst hazard in Zonguldak Coal Basin of Turkey, and association with geological parameters
土耳其Zonguldak煤田煤与瓦斯突出灾害以及相关地质参数
Natural Hazards, May 2014
Abstract: Coal and gas outbursts have been a major geological hazard to underground coal mining for over 150 years and continue to cause serious problems in all over the world. In order to have a better understanding of the phenomenon, it is worthwhile making a historical review of the occurrences and a combat of the events. Many investigations and researches have been done to characterize and prevent the outburst occurrences in the worldwide, but there has been no detailed investigation about coal and gas outburst occurrences in Turkey. This paper presents the outburst data of coal mines in Turkey since 1969. Based on the observation of outburst occurrence in Turkey in the period from 1969 to 2012 as well as mining and geological conditions, detailed analysis of the possible causes of outburst accidents is conducted. The influences of some geological parameters such as the depth of occurrence, thickness and inclination of coal seams, the amount of ejected material (coal and gas), and tectonic disturbances on coal and gas outburst occurrences have been statistically investigated. The outburst occurrences throughout the world were reviewed and compared with the Turkish outburst experiences. Suggestions are put forward on future studies that could be of interest to government agencies regarding strategic policies, proper technical management practice, identification of outburst-prone coal seams, as well as prevention and control measures.
Calculation of periodic roof weighting interval in longwall mining using finite element method
基于有限元法的长臂开采顶板周期来压间隔计算
Arabian Journal of Geosciences, May 2014, Volume 7, Issue 5, pp 1951-1956
Abstract: The state of periodic loading and the interval of periodic roof weighting have an important role in geomechanical stability and, hence, in the continuity of longwall mining operations. In this paper, the mechanism of roof caving in longwall mining—together with the effect of engineering and geomechanical properties of surrounding rock masses on the magnitude and timing of periodic loading—is studied. For this purpose, a longwall mine is first modeled using Phase2 software, and then, by simulating the roof caving process, the periodic roof weighting intervals is calculated. Based on the numerical modeling, the first roof weighting interval and the periodic roof weighting interval are calculated as 27.2 and 12.1 m, respectively. Sensitivity analysis is then applied to determine the effect of changes in the mechanical properties of the rock mass, especially in the main roof and immediate roof. The results of the analysis show that as GSI and quality of the immediate roof increases, the periodic roof weighting interval also increases. Hence, the applied algorithm in this research study can effectively be utilized to calculate the periodic roof weighting interval in the longwall mining method.
The characteristics of deformation and failure of coal seam floor due to mining in Xinmi coal field in China
中国新密煤田开采引起的煤层底板变形与破坏特征
Bulletin of Engineering Geology and the Environment, April 2014
Abstract: Deformation and failure of a “three-weak” (weak roof, thick weak coal, and weak floor) coal seam floor subject to mining are studied in this paper. Firstly, by using a group of strain sensors buried at different floor depths, we measured the relationships of the axial strain to the distance from the advancing face field. The floor depths and stratum positions, and as well as the peak width, which is the distance of the first maximum strain increment to the working face, were drawn. The axial stress and its zone of influence, which is the distance from the face to the borehole along the roadway, and at which there is obvious strain increment difference, were also drawn. Secondly, we established an analytical mechanical model and found the analytical solution of the floor’s supporting pressure distribution ahead of the face. And thirdly, we set up a numerical simulation engineering geological model and simulated stress distribution and deformation characteristics of the floor with complex multi-stratum (11 strata) structure. The results from the three approaches showed that: (1) the failure depth (<10.0 m) and zone of influence (up to 36.0 m) induced by mining ahead of the three-weak seam face were much smaller than those common seam faces; (2) the axial strain fluctuated greater than the radial one, with its max peak keeping at about 8.0 m ahead of the advancing face, and its zone of influence spreading to 36.0 m; (3) the peak width of axial strain and its zone of influence in the haulage roadway were stronger than those in the ventilation roadway; and (4) the three weak coal seam played a strong buffering action against deformation and failure due to mining. This research may be of interest to assist with improving strata control and health and safety in operating coal mines.
Empirical Approaches for Design of Web Pillars in Highwall Mining: Review and Analysis
边帮开采网柱设计实证方法：综述与分析
Geotechnical and Geological Engineering, April 2014, Volume 32, Issue 2, pp 587-599
Abstract: Pillar design is of paramount importance to any underground mine design. Oversized pillars may lead to loss of coal while undersized pillars may lead to instability. While underground pillars are mostly square and rectangular, highwall mining pillars are long and narrow, as they are formed after driving parallel entries in the seam from the highwall. These pillars are termed as web pillars. The overall stability of highwall depends upon these pillars as no other supports are provided in the entries. Web pillar differs from usual coal pillars in respect of w/h ratio being <3.0, with an exceptionally longer length compared to its width, to the tune of 50–500 m. Several empirical coal pillar strength equations developed for rectangular pillars are still being used with some modifications to adapt to web pillars. Review and analysis of these empirical approaches for determining web pillar strength along with a numerical approach for web pillar design are discussed in this paper. Their application to some Indian case studies is also discussed.
Identification Model and Indicator of Outburst-Prone Coal Seams
易突出煤层的识别模型与显示器
Rock Mechanics and Rock Engineering, March 2014
Introduction: Coal and gas outburst with a sudden and violent ejection of a large amount of coal and gas from the working face is the most harmful dynamic phenomenon during coal mining (Aguado and Nicieza 2007; Lama and Bodziony 1998; Toraño et al. 2012). Outbursts have occurred in all the major coal-producing countries around the world; however, nearly one-third of the total outbursts have occurred in China (Guan et al. 2009; Skoczylas 2012; Xu et al. 2006).
The process of judging the possible occurrence of coal and gas outburst in the near future is defined as the identification of outburst-prone coal seams, which is of great significance for underground mining safety. The identification of outburst-prone coal seams can be conducted before or after the occurrence of dynamic phenomenon. Since the vast majority of coal seams do not show dynamic phenomenon, it is necessary to identify outburst-prone coal seams before the occurrence of dynamic phenomenon. To this end, many dynamic character
Deformational criteria for the stability of roof rocks and rock bolts
顶岩与岩石锚杆稳定性的变形标准
Journal of Mining Science, March 2014, Volume 50, Issue 2, pp 260-264
Abstract: The authors discuss issues of stage-wise rock bolting of mine workings. Using equivalent material models, permissible roof rock lamination for roof bolting in conformity with the excavation support standards is evaluated. The critical displacements of roof rocks that make stage-wise roof bolting impossible are calculated.
The fracture mechanism and acoustic emission analysis of hard roof: a physical modeling study
坚硬顶板的破坏机理与声发射分析：物理模拟研究
Arabian Journal of Geosciences, April 2014
Abstract: Roof fracture has been a persistent threat to coal mine safety. In this paper, a physical modeling system was established to explore the fracture mechanism of the hard roof. The characteristics of acoustic emission (AE) signals during the process of hard roof failure were also studied. Results indicate that shear failure first occurs in the two ends of the hard roof beam due to the comprehensive effect of ground stress and mining-induced stress. After this failure occurs, the bending moment moves quickly toward the middle of the beam. This movement will cause tensile failure in the middle part of the beam. Broadband frequency signals are produced when a hard roof is fractured. When compared with AE energy, the AE count shows an increasing trend during a short period before each hard roof fracture. AE signals, especially for AE energy, increase steeply, reaching a peak value at the moment rock fracture occurs. These signals then drop rapidly, ending with a weak level until the next turn. Both the periodic characteristics and evolution process of AE signals can reflect not only the stress state but also the damage degree of the roof strata. These results could offer some thoughts and reference for forecasting and monitoring rock bursts caused by hard roof failure.
Geo-stress Fields Simulated with 3D FEM and Their Qualitative Influence on Coal and Gas Outburst
基于3D FEM的地质应力模拟以及其对煤与瓦斯突出的定性影响
Geotechnical and Geological Engineering, April 2014, Volume 32, Issue 2, pp 337-344
Abstract: Coal and gas outbursts took place about thirty times at one coal mine in China, which not only caused safety problems but also hindered the regular production in different degree. In-situ geo-stresses of two points are successfully measured near coal and gas outburst locations, and the measured maximum principal stress is approximately at the horizontal direction, while the minimum principal stress is at the vertical direction. A three-dimensional model is built with FEM software of ANSYS, the measured geo-stress are taken as boundary pressures to be applied on the FEM model, and the geo-stress fields in the coal seam are calculated. In the end, the qualitative influence of the maximum principal geo-stress on coal and gas outburst is analyzed based on the relationship between geo-stress and number of coal and gas outburst.
Evaluation of directional drilling implication of double layered pipe umbrella system for the coal mine roof support with composite material and beam element methods using FLAC 3D
用FLAC 3D及复合材料和梁元法的煤矿顶板支柱双层管伞系统定向钻孔技术应用评估
Journal of Mining Science, March 2014, Volume 50, Issue 2, pp 335-348
Abstract: This study demonstrates possible scenarios of double-layered umbrella pipe system installed over a longwall take down room in a western coal mine, where holes are drilled and cased from an adjacent entry in advance of undermining. Finite difference analysis in FLAC 3D with strain hardening gob model is used because this method is a complex and rigorous way for solving boundary value problems, such stress and strain in a continuum and at an excavation boundary due to undermining. Support system was simulated with two different methods: composite material method and beam element method. We realized that the composite material method is very conservative compared to beam element method. Thus, in the rest of the simulation, we used the beam element method to investigate the effect of different angles of umbrella pipes on the roof support. To validate the modeling results, we compare the numeral modeling results with empirical formula widely used in subsidence calculation. Also, this computer simulation compared displacement of roof between in the presence and absence of this pipe umbrella support system. In this paper, we demonstrated that a relative stiffness increase ∼185% for a reinforced zone can decrease the displacement ∼ 12.5 cm (∼ 5 in.) in the longwall recovery room roof based on results from the equivalent stiffness method. This reduction is a substantial amount, which could be really beneficial to mine operators during mining processes.
Mining thin sub-layer as self-protective coal seam to reduce the danger of coal and gas outburst
以开采自保护薄亚煤层来减少煤与瓦斯突出危险
Natural Hazards, March 2014, Volume 71, Issue 1, pp 41-52
Abstract: In response to the severe situation of coal mine gas disaster in China, a new method of reducing the danger of coal and gas outbursts and improving gas drainage and utilization in coal mines was introduced in this paper. The main idea of this method is to mining thin sub-layer as self-protective coal seam to eliminate or reduce the danger of coal and gas outburst. This method can be implemented by drills along seam and hydraulic jet when the mined seam with a relatively weak risk of coal and gas outbursts is soft or has a soft layer. This method was first applied in the Yian mine to verify its effectiveness. The results of application showed that mining thin sub-layer as self-protective coal seam can effectively eliminate the danger of coal and gas outburst and improve gas drainage and utilization. As this method needs less time and lower cost than conventional protective layer mining, it is of great significance for mining coal seam with the danger of coal and gas outburst.
Modelling of Longwall Mining-Induced Strata Permeability Change
长臂开采引发的层渗透性变化模拟
Rock Mechanics and Rock Engineering, February 2014
Abstract: The field measurement of permeability within the strata affected by mining is a challenging and expensive task, thus such tests may not be carried out in large numbers to cover all the overburden strata and coal seams being affected by mining. However, numerical modelling in conjunction with a limited number of targeted field measurements can be used efficiently in assessing the impact of mining on a regional scale. This paper presents the results of underground packer testing undertaken at a mine site in New South Wales in Australia and numerical simulations conducted to assess the mining-induced strata permeability change. The underground packer test results indicated that the drivage of main headings (roadways) had induced a significant change in permeability into the solid coal barrier. Permeability increased by more than 50 times at a distance of 11.2–11.5 m from the roadway rib into the solid coal barrier. The tests conducted in the roof strata above the longwall goaf indicated more than 1,000-fold increase in permeability. The measured permeability values varied widely and strangely on a number of occasions; for example the test conducted from the main headings at the 8.2–8.5 m test section in the solid coal barrier showed a decline in permeability value as compared to that at the 11.2–11.5 m section contrary to the expectations. It is envisaged that a number of factors during the tests might have had affected the measured values of permeability: (a) swelling and smearing of the borehole, possibly lowering the permeability values; (b) packer bypass by larger fractures; (c) test section lying in small but intact (without fractures) rock segment, possibly resulting in lower permeability values; and (d) test section lying right at the extensive fractures, possibly measuring higher permeability values. Once the anomalous measurement data were discarded, the numerical model results could be seen to match the remaining field permeability measurement data reasonably well.
Evaluation of Top Coal Yielding Potential in Longwall All Top Coal Caving Mining
长臂全放顶煤开采中顶煤屈势评估
Mine Planning and Equipment Selection, 2014, pp 143-149
Abstract: Longwall Top Coal Caving (LTCC) is a method of extraction for underground mining of thick coal seams. This method, being a combined version of Longwall and Sublevel caving methods, has a higher output than a single longwall face. This is because coal is not only extracted by shearer loader but also produced by simultaneous caving of the remaining top coal behind the powered supports. Cavability is one of the most important parameters that control the applicability of the LTCC method. The correct understanding of the top coal failure mechanisms and caving characteristics are therefore the key factors for successful LTCC operation. In this paper, a yield criterion based on in-situ stress conditions and the Hoek-Brown rock failure criteria is developed. This criterion evaluates cavability by estimating yielding potential of the top part of the coal seam. The results of this research as well as the methodology adopted can serve as useful tools for a successful operation of the high output high recovery LTCC method.
The Mining Technology of a Thick Overburden Layer Covering a Group of Flat Dipping Coal Seams
厚覆盖层缓倾斜煤层开采技术
Mine Planning and Equipment Selection, 2014, pp 75-80
Abstract: Horizontal mineral deposits with relatively thick sediment overburden advisable to practice using transtoptless overburden removal technology, that is using a powerful stripping equipment - draglines. The main advantage of this technology is the placement of overburden directly into cut goaf, significantly reducing the rented for the waste dumps disposing areas, and reduce the costs of mining - reclamation works.
Analysis of Roof Caving Characteristics at a Coal Mine by Using Full Scale 3D Numerical Modeling
基于全尺度三维数值模拟的煤矿顶板垮落特征分析
Mine Planning and Equipment Selection, 2014, pp 501-509
Abstract: Regular and efficient caving of roof strata behind is essential in maintaining a trouble free operation in underground longwall mining when especially mined area is left for caving. As the face advances, roof strata should be regularly caved forming a goaf as homogenous as possible. In case of having an uncaved roof behind the coal face, load on the face increases dramatically leading to serious fall of roof conditions. Therefore it is of paramout importance to have the roof regularly caved behind a longwall face. This paper presents the problems encountered at a coal mine in Turkey due to high face pressures and subsequent flow of roof at the face roof junction. The height of the fully mechanised longwall face is 4.5 m. Sliding of face coal and later the fall of roof strata in front of the shields created serious stability and safety problems in the mine. Stopes opened in the roof had to be filled by usign forepoling, foam and concrete. This rescue operation had to be completed securely before starting of the cutting operation at the longwall face. Obviously rate of production of the longwall face has been severly declined during this period. There were a couple of reasons for having such a difficult condition in the mine. The longwall panel was located near to a syncline axis leading to high tectonic stresses. There were lots of small faults through the working face. Longwall face was extremely loaded by a very strong limestone layer having a thickness of up to 80 m located at 120 m above the coal seam. Although the strata between the limestone layer and the coal seam has a readily caving characteristics, the limestone caved at long intervals causing high face pressures due to its cantilever beam effect. Moreover during caving of the limestone, severe dynamic loads are experienced in the vicinity of longwall face deteriorating stability conditions. Therefore it was decided to model the effect of limestone layer’s behaviour by means of numerical modelling. A full scale model was created in accordance with all geometrical conditions and operational parameters by using FLAC3D software. The face advance is also simulated on the model. Stress and deformation state of the coal face, surrounding rock and especially the problematic limestone layer are analysed. To solve the problem, a blasting pattern is selected to weaken the limestone layer by using drill holes opened from the surface. This paper presents the numerical modelling results in relation to selection of the best blasthole geometry to decrease loading on the face and hence maintain a safe, efficient and stable longwall operation.
Early-Warning of Rockbursts Based on Time Series Analysis of Electromagnetic Radiation Data
基于电磁辐射数据时序分析的岩石突出预警
Mine Planning and Equipment Selection, 2014, pp 521-527
Abstract: Based on time series analysis of electromagnetic radiation (EMR), an EMR model of rockburst early-warning was established to quantitatively analyze EMR trends and characterize EMR precursors before an impending rockburst phenomenon, with the goal to improve the EMR prediction accuracy of a rockburst danger. The model includes two parts: one is warning criterion of EMR abnormity based on normal distribution of mean and variance parameters; the other is the risk identification method based on trends forecast utilizing time series analysis. It has been applied successfully at the No.237 working face in Hegang coalmine. The results show that the model can quantitatively determine the degree of rockburst risk and identify hazardous area, which provides a profound basis for the quantitative identification of electromagnetic radiation precursor and accurate prediction of rockbursts.
Numerical modeling of time-dependent closure of coal seam artificial fractures
煤层人工裂缝时间相关闭合数值模拟
Journal of Coal Science and Engineering (China), December 2013, Volume 19, Issue 4, pp 441-453
Abstract: In order to improve efficiency of coal seam gas drainage, many fracturing techniques, such as waterjet fracturing, hydraulic fracturing and explosive fracturing, etc, have been developed and widely used in China coal mining industry. However, during the engineering applications, it is observed that the efficiency of gas drainage initially improves, but reduces thereafter. Thus, it is speculated that the contrasts in coalbed methane drainage efficiency may reflect variation of the closure behavior of the artificial fracture created. Based on comprehensive gas drainage monitoring data in underground coal mines, the work presented herein uses numerical simulation to show the behavior of the time-dependent closure of coal seam fractures associated with various levels of waterjet fracturing parameters and geomechanical conditions.
Strata-pressure behavior of double-unit mining method combining fully-mechanized and mechanized coal face
双工作综采面层压特征
Journal of Coal Science and Engineering (China), December 2013, Volume 19, Issue 4, pp 454-461
Abstract: Based on the engineering background of double-unit face mining under complicated geological conditions and the lagging fully-mechanized face surpassing the fore mechanized face of double-unit face in Zhou Yuanshan coal mine, strata-pressure behavior in the process was analyzed based on FLAC3D and on-site measurement. The results show that the stress concentration factor of superposition abutment pressure and the alternate distance of double-unit face are meeting gauss function, the relationship between the depth of stress concentration point and alternate distance also meets gaussian function. When the alternate distance is larger than 24 m, the superimposition of pilot support pressure in the double-unit face is weak. When the alternate distance is more than 12–15 m, the changes of the roof subsidence coefficient and the depth of stress concentration point are stabilized; when the alternate distance is 3–6 m, the fore working face end is in the greatest impact area of superposition abutment pressure, this area should be avoided in determining the reasonable alternate distance.
Coal Mine Roadway Stability in Soft Rock: A Case Study
软岩煤矿巷道稳定性：实例研究
Rock Mechanics and Rock Engineering, December 2013
Abstract: Roadway instability has always been a major concern in deep underground coal mines where the surrounding rock strata and coal seams are weak and the in situ stresses are high. Under the high overburden and tectonic stresses, roadways could collapse or experience excessive deformation, which not only endangers mining personnel but could also reduce the functionality of the roadway and halt production. This paper describes a case study on the stability of roadways in an underground coal mine in Shanxi Province, China. The mine was using a longwall method to extract coal at a depth of approximately 350 m. Both the coal seam and surrounding rock strata were extremely weak and vulnerable to weathering. Large roadway deformation and severe roadway instabilities had been experienced in the past, hence, an investigation of the roadway failure mechanism and new support designs were needed. This study started with an in situ stress measurement programme to determine the stress orientation and magnitude in the mine. It was found that the major horizontal stress was more than twice the vertical stress in the East–West direction, perpendicular to the gateroads of the longwall panel. The high horizontal stresses and low strength of coal and surrounding rock strata were the main causes of roadway instabilities. Detailed numerical modeling was conducted to evaluate the roadway stability and deformation under different roof support scenarios. Based on the modeling results, a new roadway support design was proposed, which included an optimal cable/bolt arrangement, full length grouting, and high pre-tensioning of bolts and cables. It was expected the new design could reduce the roadway deformation by 50 %. A field experiment using the new support design was carried out by the mine in a 100 m long roadway section. Detailed extensometry and stress monitorings were conducted in the experimental roadway section as well as sections using the old support design. The experimental section produced a much better roadway profile than the previous roadway sections. The monitoring data indicated that the roadway deformation in the experimental section was at least 40–50 % less than the previous sections. This case study demonstrated that through careful investigation and optimal support design, roadway stability in soft rock conditions can be significantly improved.
Developing a new model based on neuro-fuzzy system for predicting roof fall in coal mines
基于神经模糊系统的煤矿顶板垮落预测模型开发
Neural Computing and Applications, December 2013, Volume 23, Issue 1 Supplement, pp 129-137
Abstract: Roof fall is one of the most important problems connected with underground coal mines because it plays a significant role in financial and human losses. Hence, it is essential to accurately predict the roof fall rate for the purpose of controlling, reducing, and/or even eliminating the risk of the involved problems. On the other hand, there are many different parameters that make a considerable impact on the occurring roof rate. Most of these factors are not completely known or measurable. Therefore, the problem of predicting roof fall is vague, sophisticated, and complex. Adaptive neuro-fuzzy inference system (ANFIS) is a powerful and robust tool for modeling linear and non-linear patterns in science and engineering problems. In this paper, the ANFIS system is applied to model the roof fall rate in coal mines. The constructed model uses the subtractive clustering method to generate fuzzy rules based on 109 data of roof performance from US coal mines. The results demonstrate that prediction of roof fall rate by the ANFIS model is satisfactory.
