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In China,many mining areas with extremely thick and hard rock strata has strong mine earthquake and strong rock burst caused by the movement of extremely thick and hard rock strata which have serious consequences,is difficult to be controlled and has become the main obstacle to mine safe production.Based on the analysis of the occurrence law of rock burst under extremely thick and hard rock strata, the paper puts forward three common characteristics of rock burst in such mines: "the effect of key working face", "the effect of vibration-induced rock burst"and "the effect of rock burst and vibration. ""Key working face "means that the mining of this working face will lead to the fracture and strong movement of extremely thick and hard rock strata and the occurrence of strong earthquake or rock burst. "The effect of key working face"refers to the strong dynamic disasters occurring in the mining process of "key working face". "The effect of vibration-induced rock burst"refers to the rock-burst hazards caused by the dynamic stress which generated by the fracture and vibration of extremely thick and hard rock strata propagating to the coal body in the high stress state. Its feature is that "the location of the source is different from that of rock burst. ""The effect of rock burst and vibration"means that when the key working face is mined, the transmission pressure of extremely thick and hard rock strata will increase sharply.When part of the coal reaches the condition of rock burst, the rock burst will occur and cause vibrations with great energy. The characteristic of this kind of rock burst is that" the location of the source is the same as that of rock burst. "Using the theory of overlying strata spatial structure, surface subsidence observation and monitoring data of microseism and stress, a method for identifying the key working face is proposed. This paper describes the concrete methods of preventing rock burst and ensuring safety in three different types of mines with extremely thick and hard strata and the possibility of rock-burst disasters in Shandong Energy Group. These methods include protection layer mining, negative coal pillar design,determination and parameter design of key working face, mining design to avoid the boundary of vibration damage, small coal pillar design and parameter optimization design of sequential mining face. [ABSTRACT FROM AUTHOR]

Coal mining involves extracting the resources from the earth. It will disturb the strata in the mining area, which inevitably causes strata movement and the change of stress and fracture fields, thus affect safety and environmental such as the occurrence of ground pressure, groundwater loss and surface subsidence. Therefore, mining-induced strata movement and its influence on safety and environment are the basic scientific problems of coal mining. The understanding of these laws will improve the scientific nature of coal mining. Because of the complexity of strata movement, however, there are still several issues to be addressed. This paper introduces the mining-induced strata movement of the block structure, which is followed by the review of advances and outstanding issues in the influence of strata movement on longwall face support, mining-induced fractures evolution, groundwater, surface subsidence, and mininginduced stress field. It is found that mining-induced strata movement is a combination of stress concentration caused by the span of thick and hard strata and the mechanical behaviors of the rock blocks associated with the breakage of the strata. During the collapse of thick strata and the corresponding rock block movement, the characteristics of mutations and discontinuities typically occur. In such a process, a structure that can sustain large deformation may be formed after the rock blocks are hinged. The “R.-S” stability of the structure causes significant influence to such phenomena as the occurrence of ground pressure, mining-induced fractures and surface subsidence. Mining-induced strata movement is like a “black box” system. Currently it is just explained in the aspect of control principle, and reaches the level of a “gray box” system. Therefore, strata control refers to “macroscopic” control in many engineering cases. The Voussoir Beam model has established longwall support theory and the estimation principle of support working resistance. In a general case, the support resistance that is determined as the weight of the overburden with a thickness of 4 -8 times the mining height could meet the safety requirements of most mining projects. Specially,8 times should be chosen for the longwalls with a large mining height or a thin immediate roof, a shallow cover depth,or the support crush risks. As for some particular conditions, however, support crush cannot be avoided by the single measure of increasing support resistance, but should be combined with other engineering precautionary measures. According to the stability of rock blocks of overburden key strata, three types were proposed to characterize surface subsidence for varied alluvium conditions in different areas of China. It is suggested that subsidence type should be considered during the selection of subsidence prediction, control and reclamation methods. The presence of key strata and the corresponding breakage characteristics play a vital role in the distribution of mining-induced stress. At present, the prevention of accidents caused by stress concentration is harder than that of methane accidents. With this in mind, it is suggested that only test-style mines could be established in the areas with tectonic stress concentration or a large depth. This paper points out the direction for the study of strata movement and the corresponding influence on safety and environment in the coal mining industry. [ABSTRACT FROM AUTHOR]

Groundwater reservoir technology is a vital way to achieve both efficient mining and water conservation in western coalfields in China. The stability of coal pillar dam is an emphasis of reservoir design, which plays an important role in the stability of groundwater reservoirs. Coal pillar dam should ensure the safety of coal mining, as well as the safe operation of groundwater reservoirs. The stability of coal pillar dam is closely related to water weakening and engineering geological conditions, such as buried depth, mining stress, geological structure and so on. In order to study the strength weakening law of coal pillar dam of groundwater reservoirs under water, this paper took Madiliang mine No.5 in western mining area as the research object, carried out a non-destructive water immersion test on coal sample and a uniaxial compression test on coal sample under various water content and repeated soaking. The results show that the water content of coal samples with various water content increased rapidly within 0-20 h; after 20 h, the grew rate slowed down; and in 20-70 h, the water content grew slowly; in 70-140 h, the growth of water content of coal sample was nearly stable. In conclusion, the water content of coal sample increases with the soaking time, but the increase rate gradually decreases, and finally tends to be flat. With the increase of water content( the number of times of soaking), the uniaxial compressive strength of coal sample decreases gradually, but the peak strain increases gradually, and the elastic modulus decreases gradually. Compared with the dry coal sample, the uniaxial compressive strength of the first water-saturation coal sample and the coal sample with the third soaking decreased by 27.1% and 50.0% respectively, and the elastic modulus decreased by 34.6% and 58.5% respectively. Combined with the above results and the elasticplastic mechanics theory, this paper discussed the damage zone and plastic zone width of coal pillar dam under various water content, carried out the research of coal pillar dam width considering overburden rock pressure, water pressure and water weakening, and designed the width of the groundwater reservoir combining with the engineering geological conditions of Madiliang mine. At the same time, the paper further analyzed the influencing factors of the width of coal pillar dam, concluding that the width of coal pillar dam is closely affected by water content, buried depth, and mining thickness. [ABSTRACT FROM AUTHOR]

In Yushenfu mining area, the concept of water-preserved coal mining is based on the groundwater level decline and vegetation degradation caused by coal mining in the early stage. After theoretical research and engineering practice in many years, a key technical system for water-preserved coal mining has been initially established, which effectively guides the exploitation of coal resources and ecological environment protection in the ecological fragile mining areas. Under the high standards for the construction of national ecological civilization, the ecological environment protection of coal-water resources symbiosis areas in the arid and semi-arid regions of western China is facing a historical test. This paper reviewed the achievements of water-preserved coal mining technology, and concluded that the research on geological conditions, rock movement and water-preserved coal mining methods had basically solved the outstanding problems in single coal seam mining, while the investigation on water and ecological constraints on coal mining, and ecological restoration and reconstruction lagged slightly behind. By combing the relevant contributions, this paper explores the scientific issues in the study of five water-preserved coal mining and related fields. This includes the ecological constraints identification, the quantification and monitoring of the groundwater dependent on the mining area, the detection and prediction of the water conducting fissure zone under the conditions of large mining height and repeated mining, the quantification and evaluation of the thickness of the effective aquiclude, the overburden control and ecological reconstruction and restoration. Under the new situation, the responsibility and tasks of ecological protection in mining areas are significant. More research is needed to support the water-preserved coal mining in western China and promote the construction of green mining areas. [ABSTRACT FROM AUTHOR]

Currently more coal resource is buried in deep and more high-quality resource is located in the west of China. It makes a deep mining and a mining in the west become the new normal of coal resources exploitation. Thus a green mine construction, green mining development and green mining propulsion are imperative. This paper puts forward a"mining-dressing-backfilling+X"technical conception of green mining of coal resources. That is an underground integrated production system, which is integrated coal mining, coal-waste separation, and gangue backfilling with "active control of strata movement, gob-side entry retaining, gas extraction, disaster prevention, water-preserved-mining". The system forms a coal mining-dressing-backfilling+X(control, retain, extraction, prevention and preserved) collaborative production mode. The paper defines the"mining-dressing-backfilling+X"technical connotation and framework of greenmining, expounds "mining-dressing-backfilling+X"evolution of four generations, analyzes the specific technical advantages of its practice of green mining and gives the scientific engineering design method. The paper elaborates five aspects of typical "mining-dressing-backfilling + X"technology corresponding technical principle, engineering requirements, design process and methods, key technology and process equipment. Engineering practice of the Tangshan Coal mine, Zhaizhen Coal mine and 12 th Coal mine of Pingdingshan Group has respectively proved that "mining-dressingbackfilling+ control", "mining-dressing-backfilling + retain", "mining-dressing-backfilling + extraction " technologies have a remarkable technical superiority and the engineering demonstration effect. "Mining-dressing-backfilling + X "green mining extension in the future combines "mining-dressing-backfilling+processing", "mining-dressing-backfilling+intelligent", "mining-dressing-backfilling+adjustment"and "mining-dressing-backfilling +coordination". The overall formation of the "mining-dressing-backfilling+X"technology system can provide a strong technical support for the realization of green mining of coal and associated resources. [ABSTRACT FROM AUTHOR]

Rock burst occurring in deep coal roadway is a technical problem to be solved, 85% of which occurs in the roadway, and its frequency and intensity increase dramatically with the increase of mining depth. This paper analysis the instability mechanism of deep coal roadway roof based on the elastic-plastic mechanics and fracture principle, expounds the rupture instability mechanism of roadway roof strata with increasing stress and energy, derives the load, deformation and energy conditions of rock burst, and elaborates the fission instability evolution law of composite roof which turns roof into the vicious circle of "interlayer separation-rock beam cracking-dynamic crack by dynamic load" or even instant caving. The instability process of deep coal roadway roof is closely related to the cooperatively extension of six main cracks under the superposition action of high stress and dynamic pressure. The six cracks of "one horizontal and five vertical" extend together and form a "door" -like breaking block to push into roadway and cause damage. The paper presents the six manifestation pattern of rock burst and dynamic instability, puts forward the effective unit control timbering countermeasure of ‘‘roof truss cable+roadway center long cable+roadway drift angle bolt”. [ABSTRACT FROM AUTHOR]

The change of coal permeability related to gas pressure is important to coal mining and CBM exploitation.The permeability evolution of various kinds of coal is different and changes with stress conditions. To investigate the permeability evolution of coal samples changed in gas pressure, the strain and permeability of coal samples collected from the No.9 coal seam in Zhaogezhuang mine,Kailuan,China were measured during gas pressure reduction under constant temperature, axial and confining stress by using Triaxial servo-controlled seepage rig.The experimental results showed that coal shrinkage strain increased with the decrease of gas pressure.And the permeability of coal cores may increase gradually or decrease firstly and then increase( The gas pressure cor-responding to permeability rebound is less than 1.0 MPa).When the gas pressure reduced to 0.3 MPa,the perme-ability was 1.9-2.9 times of the initial condition( gas pressure was 2.0 MPa).Considering that coal axial and radial strains are approximately equal,a theoretical model was established to describe the permeability evolution of the three-dimensional deformation coal.The model also reflected the effects of gas pressure and gas desorption on coal permeability.The analysis showed that in the process of reducing gas pressure, the permeability of coal will change from decreasing to increasing at a certain gas pressure( rebound gas pressure pr). The equation of rebound gas pressure pr was derived.It indicated that prwas determined by coal volume modulus ,K, and Langmuir coefficients related to the adsorption, εpand pL.The greater volume modulus K and the adsorption deformation coefficient εpare, the higher pris.And prwas independent of the external stress and the internal gas pressure. According to the derived permeability model, the permeability curves and the rebound gas pressure pr of coal samples under various stresses and gas pressures were calculated by referring to the experimental data of this paper and other published articles. The numerical results were close to the experimental data with a maximum relative error less than 8.9%.The trend of coal permeability changing with gas pressure in the experiment depends on the rebound gas pressure prand the experimental gas pressure.When pr≥pmax( the maximum gas pressure in the experiment), coal permeability decreases with gas pressure increasing.When pr≤pmin( the minimum gas pressure value in the experiment), coal permeability increases with gas pressure.When pmin

The energy endowment characteristics of "relatively rich in coal, poor in oil, less natural gas, and uranium deficiency"in China result in that the coal resources as the China’s main energy will not change in the short term.Meanwhile, the relatively abundant coal resources are still the most stable and cost-effective competitive minerals in China.There should be a clear understanding that it is unrealistic, unwise and unscientific to abandon the actual energy choices based on coal to solve China’s energy problems. However, it should be noted that the coal resources have brought about environmental pollution, ecological damage, waste of resources, and high emissions in the whole process from geological exploration to development and utilization.Therefore, the development of the coal industry in China will certainly undergo some significant changes in the new era.Implementing scientific exploration and development, clean utilization, and low-carbon consumption, characterized by science, safety, ecology, high efficiency, standardization, digitization, and intelligence, is the only way to realize the sustainable development of China’s coal industry.Aimed at the challenges and opportunities for the coal industry in China, the present situation and existing problems of coal resources in the whole process from geological exploration to development and utilization is analyzed, and the strategic thinking of building an upgrade version of main energy( coal) industry in China is proposed.In this paper, the authors focus on 11 key scientific and technological problems faced in the process of realizing the upgrade version of China’s main energy( coal) industry, namely the problems of comprehensive coordination, green exploration, deep exploration, and intelligent exploration for coal resources in the process of geological exploration; the problems of green, safety, recovery rate, occupational health, and high benefit in the coal development process; the clean and low-carbon problems in the process of consumption and utilization.Meanwhile, the corresponding exploratory solutions are put forward.It is of great theoretical significance and practical value to promote the transformation and upgrading for China from a large coal producing country to a powerful coal industrial country, and also to address the sharp contradiction between China’s current economic and social development and the protection of ecological environment. [ABSTRACT FROM AUTHOR]

The protection and utilization of groundwater resources in coal mining process is the prerequisite and necessary condition for realizing green mining at the ecological fragile mining area in western China. Among them, the extensive application of water-preserved mining and underground reservoir technology provides the possibility for solving the problem of coal-water co-production. In this paper, with the background that the stability of the coal and rock boundary of underground reservoir changed under the conditions of repeated immersion in water, the sandy mudstone of the No.3-1 coal seam roof of Wulanmulun Mine was investigated. The natural water absorption law of the sample was obtained by non-destructive water immersion test, and the water immersion time of the sample water content reaching saturation state was obtained. According to the immersion time, the sample was dried-saturated and repeatedly immersed in water. It was found that the water content increased exponentially with the number of immersion, whereas the shear strength and the number of water immersion in the sample decreased exponentially. The cohesive force decreased with the increase of the number of immersion times, while the internal friction angle increased first and then decreased, indicating that the uniformity of the material, and the shape of the fracture surface and the shape, size and direction of the fracture caused the internal friction angle to increase. The cycle immersion later was the dominant factor to make the internal friction angle decrease. Based on the relationship between cohesion, internal friction angle and number of dry-saturated cycles, the Mohr-Coulomb criterion was established based on the number of dry-saturated cycles. The acoustic emission counting curve had a strong correspondence with the shear stress curve. The acoustic emission event increased significantly at the moment of sample failure, corresponding to the obvious rising phase of the cumulative acoustic emission counting curve. The sample mainly had a low RA value during the failure process, and the failure time corresponded to a high RA value, i.e. , the common type of crack in the failure process of the specimen was tensile crack, and the moment of failure corresponded to the obvious shear crack. These results show that the strength of coal and rock pillars in the groundwater reservoir boundary changed significantly under the action of water immersion-water loss during the impoundment-pumping process in the groundwater reservoir. It is suggested that the weakening effect of water on the strength of boundary coal and rock pillars should be considered when constructing the underground reservoir. [ABSTRACT FROM AUTHOR]

Water resources destruction and geological environment changes caused by mining in ecologically fragile areas of western China have seriously restricted the sustainable development of economy, society and environment in mining areas. Through reviewing the research progress of water-preserved coal mining and carrying capacity of geological environment in coal mining areas, and combining with the current situation of geological environment in western China rich in coal and short of water, the research framework of carrying capacity of geological environment based on the concept of water-preserved coal mining is proposed. It is considered that the function mechanism of "coal mining activity-water resource destruction-geological environment effect"should be systematically analyzed by combining the concept of water-preserved coal mining with the theory of carrying capacity of geological environment. The methods of attribute analysis, ecological demand analysis, numerical analysis and catastrophe theory should be used in studying the carrying capacity of geological environment. In particular, the quantitative method, comprehensive evaluation method and the classification method of carrying status and carrying capacity of geological environment should be investigated. By means of simulation experiment, the relationship data between the geological environment and the critical value of mining intensity under the carrying capacity of typical coal mine area are obtained. Then the technological method of coal mining under water-containing for controlling and alleviating the geological environment problems in coal mine area is extracted to determine the reasonable mining intensity and scale. On the basis of the research of carrying capacity, this paper put forward the collaborative monitoring method for the influencing factors of carrying capacity of geological environment, and the criterion of bearing capacity early warning grade of carrying capacity. The connotation and basic research ideas of geological environmental carrying capacity based on the concept of water-preserved coal mining will enrich the scientific connotation of water-preserved coal mining and geological environmental carrying capacity, and provide a theoretical and technical support for the coordinated development of coal resources and water resources protection in the fragile ecological environment areas of western China. [ABSTRACT FROM AUTHOR]

Yushenfu coal field is located in the Maowusu Desert and the Loess Plateau convergence zone in China, where ecological environment is fragile and ecological water resources are scarce. The heterogeneous distribution of main aquifers and mine water inflow influence the safe production of coal mines. Thus, the protection and uti-lization of water resources are of significance to coal mine production and ecological construction. After analyzing the distribution and water abundance of the main aquifers, such as Salawusu Formation, burnt rock and weathering bedrock, combining the thickness of overlying bedrock and water inflow on field, the operating coal mines and unplanned areas could be divided into four types which are the areas of water scarcity, water richness, water abundance and surface water source. The study area has been divided into sub-regions according to the classification and their distribution. Based on the classification, the concrete measures for water preservation and mine water utilization have been proposed such as storage and purification in goaf area, industrial utilization, agricultural irrigation, wetlands construction and artificial lakes. In the paper, the scientific content of water-preserved mining has been extended and interpreted as that both preserving shallow main aquifers and effectively utilizing coal mine water resource should be taken simultaneously. It proposes that mining damage and ecological self-repair should be considered before coal mine construction. It also proposes that the idea of using economic benefits to repay the local ecosystem and green economy which provides certain references for mining area planning and construction. [ABSTRACT FROM AUTHOR]

Coal mining with water protection is an inevitable choice for the sustainable development of ecologically fragile mining areas. The study and application of coal mining with water protection is an urgent problem to be solved in coal development planning, construction and production in northwest China. Taking Yushen mining area in northern Shaanxi Province as an example, this paper studies the types of water-preserved coal mining coalmines in combination with the quantity distribution of shallow water resources( water-preserved coal mining target seam) and the impact of coal mining on shallow water resources. Firstly, the spatial occurrence structure characteristics of eco-water-coal measures strata in the study area are analyzed. Also, the eco-geological environment types for the purpose of water-preserved coal mining are proposed, which are divided into oasis type with phreatic water and bottomland in desert, oasis type with surface water and valley river, loess gully type with surface runoff, and regional deep groundwater enrichment type. Secondly, the distribution of total storage per unit area of shallow water resources is calculated and determined. Then, based on the influence degree of coal mining on ecological layer and shallow water, four types of environmental engineering geological patterns( basically unaffected model, gradually restored model after destruction, gradually deteriorated model and disaster model) are proposed. Based on the analysis of the key indicators affecting the division of environmental engineering geological patterns, including the height of the water-flowing fractured zone and the mining water-resisting of residual aquiclude, etc., the zoning threshold and determination method for environmental engineering geological patterns is established. Finally, based on the distribution characteristics of shallow water resources and environmental engineering geological patterns, the grade types of water-preserved coal mining coalmines are put forward for the first time, which is divided into normal mining mine, water-preserved coal mining first-class mine, water-preserved coal mining second-class mine and water-preserved coal mining third-class mine. [ABSTRACT FROM AUTHOR]

The exploitation of underground coal resources can easily lead to the loss of precious shallow water resources, which leads to the death of surface vegetation and the imbalance of ecosystem. To protect the shallow water resources( river, lake and diving of quaternary sand aquifer), which maintains the ecological environment of the western mining area, especially to protect the underground diving( ecological) water level, the concept of water conservation mining in short-distance coal seams was put forward based on the previous theoretical achievements of water conservation mining in shallow single coal seam and the experience of rock control engineering. The concept integrated the protection of ecological water level, and the prevention and control of water inrush. In order to achieve an efficient water conservation mining under the mining conditions of short-distance coal seams and extremely short-distance shallow water resources, this paper studied the technical problems, such as the collaborative control of strata water-conducting fractures in the disturbed area of repeated mining, the low-damage control of ultra-thin barrier layers and the monitoring and warning of water inrush( outburst) on mining surface. The study presented the long wall water conservation mining method, the water conservation mining under continuous mining and filling with wall system and the infrared monitoring and warning methods for water inrush in working face to realize the safe and efficient mining. More specifically, the methods included the strata control of short-distance coal seams, the calculation of the height of water-conduct fractures, the deformation calculation of aquicludes, the infrared radiation theories of loaded coal and rock, the control of water diversion fractures in the disturbed area of repeated mining, the filling body actively connected to the roof and the rapid operation technology among mining, supporting and transportation. Meanwhile, the weak areas of water conservation mining were determined. Based on water resource protection, the optimized working face layout of shallow buried and short-distance coal seams, mining method allocation and water resource movement monitoring, an efficient mining theory was formed. The achievements have been achieved in the practice of water conservation mining in north Shaanxi and north China, which provides supports for green mining in China. [ABSTRACT FROM AUTHOR]

Shenfu mining area is a China’s important coal production base and a typical high intensity mining field, and also a typical fragile ecological environment of arid and semi-arid areas, in which the burnt rock aquifer is one of the main groundwater resources. In order to study the influence and the protection of the burnt rock aquifer, taking the 5-2 coal mining in the first mining area of Zhangjiamao Mine field as an example, by studying the hydrogeological structure system and the water flowing fractured zone of 5-2 coal roof, this paper investigates the types and characteristics of water resources, establishes the water-preserved mining target of 5-2 coal seam, divides the water-preserved coal mining partition of 5-2 coal seam, and puts forward a new water-preserved coal mining technology which is burnt rock grouting curtain interception method. The results show that there are six main types of water resources in the study area, where only the burnt rock aquifer of 4-2 coal seam has the significance of water-preserved mining and the 5-2 coal mining area is divided into anhydrous mining area and water-preserved limited mining area of the 4-2 coal burnt rock aquifer. In the water-preserved limited mining area of 5-2 coal seam, the designed curtain wall spatial morphology, the position and quantity of curtain line and the row spacing and structure of grouting drilling are reasonable. In addition, the procedure and processes of drilling and grouting planed are scientific, and the implemented key technologies of grouting curtain, such as dual-site bidirectional water diversion grouting, zoning grouting of burnt rock full section, immediate test of anti-seepage and interception effect, are feasible. The pre-drainage of the 4-2 coal burnt rock aquifer of the working face before mining, and the measurement of the working face water inflow after mining in the water-preserved limited mining area of 5-2 coal seam show that the static reserve and the dynamic recharge of the 4-2 coal burnt rock aquifer water quantity are about 20 000 m3 and less than 5 m3 per hour respectively. It means the grouting curtain closure realizes the effective isolation of the 4-2 coal burnt rock water inside and outside the curtain, and greatly reduces the water discharge of the 4-2 coal-burnt rock water and the Changjiagou reservoir water with which it has direct hydraulic connection, and the protective mining effect of water resources is remarkable. [ABSTRACT FROM AUTHOR]

In the western part of China, mine disasters such as support failure, surface stepped subsidence and mine earthquake, are prone to occur when lower coal seam is extracted which is closely beneath the coal pillars left after room-and-pillar mining with shallow overburden. In this paper, physical modelling and numerical simulation method were adopted to investigate the dynamic instability process of upper coal pillar group and the mechanism of support failure under the influence of lower coal seam mining. According to the measured statistics in some mines after coal mining of Yuyang District, only when the proportion of elastic core area of the coal pillars is greater than 31% can the room coal pillars keep long-term stability. The simulation result after mining lower coal seams shows that the failure form and instability sequence of the upper coal pillars have close relations with the positions relative to the lower coal seam working face. The damage and instability of room coal pillar occur in the positions of open-off cut, working face, and the middle of goaf successively. Furthermore, the coal pillars in the open-off cut and working face mostly show horizontal shear failure, while the coal pillars in the middle of the goaf show vertical fracturing damage. According to the numerical simulation results of Shigetai Coal Mine, the peak abutment pressure of coal pillar in upper 2-2 coal seam increases from in-situ stress 2. 8 MPa to 12 MPa after coal mining with the stress concentration factor at 4. 28. After the lower 3-1 coal seam working face mined, the peak abutment pressure of the retained pillar in upper 2-2 coal seam continually increases to 30 MPa with the stress concentration factor up to 10. 71. The open-off cut side of the lower coal seam working face showed uneven horizontally bearing with the coal pillar directly above the lower coal seam working face and the influence of horizontal tensile deformation are the main reasons for the diagonal failure mode of the boundary coal pillars. After the instability of two sides coal pillars, the roof instantaneously occur overall shear breakage, causing mine earthquake, and multi-layered strata in the roof settled suddenly in the form of "rigid body motion"and hit against the floor, leading to the collapse of the room coal pillars in the middle of goaf. At the same time, the huge impact force further leads to the full cutting of the strata between the upper and lower coal seams, which results in the roof cutting and support failure in the lower coal seam working face. It was found in the experiment that there was only about 0. 45 seconds from the failure of the first coal pillar in the overlying coal pillar group to the overall unstable movement and the final stability, among them, the full cutting of the strata between the upper and lower coal seams only took about 0. 05 seconds. [ABSTRACT FROM AUTHOR]

Coal bump often occurs in the mining process between two adjacent mines under the control of large geological bodies. In order to study the coal bump mechanism between adjacent working faces of two adjacent coal mines under the condition of large fault and huge thick overburden conglomerate, this paper investigates the 23070 working face at Yuejin coal mine and the 21220 working face at Changcun coal mine in China. The analyses of monitoring data are carried out on the characteristics of coal bump behavior, microseismic spatio-temporal evolution and microseismic energy. Furthermore, the theoretical analysis and numerical simulation of stress distribution of overburden structure during the mining process of two working faces are conducted. The results show that the activation of F16 thrust fault and overall control of massive conglomerates in Yima mining area provide the stress conditions for coal bump. During the mining process of two mines’ adjacent working faces, the "asymmetric T-shaped"structure is formed between the rock beamabove the goaf and coal-rock pillar between two mines. The coal bump around the 21220 working face leads to the stress transfer onto the two mines’ pillar and the 23070 working face, which induces the coal bump around the 23070 working face. Mining disturbance between two mines leads to stress transfer and induces rock burst, which is closely related to the initial bump intensity and mining length of later working face. Finally, based on theory and engineering monitoring, a coal bump controlling technique with chain-weakening and consumption-increasing between two coal mines is put forward, which regards the weakening of the structural chain of high stress transfer as core. The results provide a theoretical basis for the study on the mechanism and control of coal bump between two adjacent working faces in two adjacent mines. [ABSTRACT FROM AUTHOR]

Carrying out mine environmental research is a concrete action to build a "beautiful China", which can turn abandoned mines into mountains with clear waters and green trees. The previous exploitation of mineral resources was at the expense of human living environment, resulting in irreparable waste of resources and destruction of ecological environment, which brought serious mine environmental problems. At present, China is faced with outstanding mine environmental problems, but the restoration progress of mine environment is relatively slow. In order to solve the mine environmental problems caused by the exploitation of mineral resources scientifically, the idea of systems engineering is adopted, and the paper means to address the mine environmental problems from the following nine aspects: classification, investigation, evaluation and prediction, restoring techniques and modes, evaluation of land suitability, monitoring and early warning, information system research and development, regulations and standards, and mine environmental management. The classification scheme of mine environmental problems and the effect characteristics of each type are put forward; and in order to standardize mine environment investigation and data collection, the technical methods and standards of field in situ investigation are established; in order to grasp the present situation of mine environment and predict the future, the methods and models for mine environment evaluation and environmental predictions for different development schemes are put forward; due to the systematic attribute of mine environment, the research on environmental problems, remediation targets, remediation technologies and remediation model has been carried out, and the restoration and treatment model of mine environment has been established; from the perspective of the restoration and reuse of mine land resources, the theory and method of land suitability evaluation after restoration and treatment are constructed; and the monitoring and early warning technology of mine environment is developed for real time monitoring, analyzing the changing trend and early warning the emergencies; in order to visually display the achievements of mine environmental remediation and to share the experiences and lessons of restoration and management, a mine environmental information management system based on cloud platform, big data and other modern information technologies is developed; the laws, regulations and standards about mine environment at home and abroad are collated, compared and analyzed; and the responsibilities of the government and enterprises in the management of mine environment are expounded. Finally, the future development of mine environment research are prospected from the aspects of elimination the negative impact on ecological environment, exploitation the positive-effect resources of closed-pit mines, economic construction and transformation of mining cities, prevention theory and methods in deep mining mines, ecological environment of underground mines, theory and technology for public safety prevention and control, setting up of mine environment platform with big data and artificial intelligence. [ABSTRACT FROM AUTHOR]

With the deep coal mining in China, the contradiction between the mine water inrush from aquifer underling the coal seam and the decline ecological water level is more and more serious. Based on the analysis of the assemblage characteristics between the No. 5 coal seam and the aquifer(auifuge) in Chenghe mining area, the present study is to investigate the depth of destroyed floor by combining the theoretical calculation and in-situ measurement. The influence of coal seam mining on the confined water underling the coal seam has been studied from the perspective of aquifer structure, ecological water level and water quality. The results indicate that the maximum depth of destroyed floor of the No. 5 coal seam is 8-10. 8 m, and the main control factors of the depth of destroyed floor are the dip length of working face and the lithologic association of floor. And there is a positive correlation between the dip length of working face and the depth of destroyed floor, a negative correlation between lithologic association of floor and the depth of destroyed floor. Influence degree of the aquifer structure from large to small can be divided into Ⅰ,Ⅱ,Ⅲ level area, and the Ⅰ level areas are mainly distributed in the central-south and north,which covers an area of 6. 78 km2,accounting for 45． 2% of the total area; there is no obvious effect on water level and water quality. The paper puts forward a grouting reinforcement technology to protect water resources and stabilize the ecological water level in mining, and finds an effective way for the healthy development of coal industry in Weibei region. [ABSTRACT FROM AUTHOR]

The deep mining of coal mines leads to some significant changes in the physical properties of coal and rock, stress environment and gas occurrence law. The perturbed range of overlying rock and level of dynamic-static load have also increased significantly. In addition, the disaster effect caused by the linkage of mine groups and the control effect of large geological bodies appear in deep mining. The same disaster effect with the coexistence and conversion of rock burst and coal & gas outburst occurs. Therefore, above characteristics make the prevention and control of dynamic disaster in deep coal mines become a problem to be solved urgently. Considering the situation that the conditions of disaster breeding and mutual transformation mechanism are complex and still unclear, the quick detection method, prevention- control technology and equipment are still lacking, in this paper, the key scientific and technical problems of prevention- control for dynamic disaster in deep mining are condensed, the thought of prevention and control with different sources in multi-scales for coal and rock dynamic disasters in deep mining is proposed, the research direction of prevention and control technology for dynamic disaster in deep mining is determined, and the theory and technical framework of prevention and control with different sources in multi-scales for coal and rock dynamic disasters in deep mining are established. Based on the above achievements, the theory and technology system of prevention and control with different sources in multi-scales for coal and rock dynamic disasters in deep mining are formed successfully, which can provide a theoretical and technical support for the prevention and control of rock burst, the outburst of coal and gas or compound dynamic disaster in deep mining of coal mines in China. [ABSTRACT FROM AUTHOR]

Goal rock is naturally comprised of a large number of randomly-distributed discontinuities such as joints/ cracks and weak interlayers. The geometry, size, distribution, contact and infillings of the discontinuities essentially govern the physical/mechanical properties and failure mechanism of coal rock. It is intractable to theoretically and accurately characterize the discontinuities and the governing influences on the deformation and failure of coal rock. This paper presented a 3D finite element model of fractured coal rock representing the irregular geometry, complex contact, intersection, and network features of interior joints and cracks by means of high-resolution GT techniques and 3D reconstruction methods. The birth-death clement algorithm was employed to characterize and visualize the stress field distribution, spatial distribution of failed areas, energy dissipation and release during the deformation and failure of fractured coal rock when subjected to the varied unloaded conditions. The analysis discloses the determinative influences of the unloading paths and the properties of joints and cracks on the macro mechanical behavior and the failure mechanism of fractured coal rock. The paper presents a promising way to identify and characterize the governing effect of unloading due to deep excavation on real fractured coal rock. [ABSTRACT FROM AUTHOR]

In this paper, the author presented a strategy for classifying local multi-channels MS waveform, triggering by a single event. There were three steps to achieve the goal. Firstly, based on STA/LTA method, the first arrival and terminated time had been picked up, using the MS signal preprocessed; secondly, the author extracted the waveform features, time-frequency (L,f), amplitude (A), statistics of amplitude distribution (AD) and threshold algorithm (TS), and correlation coefficient (R); thirdly, before establishing an effective judgment mechanism, this method employed a hierarchical recognition framework with 3 layers, which integrated preliminary judgment, combined recognition and optimization judgment. This method was validated through analyzing a coal mine visual event in Shandong Province, and the result shows that it is successfully used to classify electromagnetic interference wave, background noise and MS events. The result can basically meet the requirements of classification accuracy. [ABSTRACT FROM AUTHOR]

High-grade syngas can be produced from the reforming of CH4 with CO2. To achieve efficient conversion of reforming reaction into syngas production, the reforming of CH4 with CO2 for syngas production was conducted in this paper under microwave irradiation, with biomass char as catalyst and microwave absorbing medium. The influences of the conditions including reaction temperature, molar ratio of CO2 and CH4, addition amount of biomass char as well as the introduction of water vapor on the reforming reaction were investigated. The results reveal that an increase in the conversion of reactant gases into syngas production can be achieved through raising reaction temperature, enhancing molar ratio of CO2 and CH4 or increasing addition amount of biomass char. Raising reaction temperature results in a promotion in the ratio of H2 to CO, while enhancing molar ratio of CO2 to CH4 or increasing addition amount of biomass char bring about a decrease in the ratio of H2 to CO. And the introduction of water vapor is not only favorable for the reforming reaction, but also is responsible for an increase in the ratio of H4 to CO. [ABSTRACT FROM AUTHOR]

For the low porosity and pressure coalbed methane ( CBM) reservoirs in China, the paper adopted the technology thought of combining the temporally plugging technology of the nanomaterials with circulative micro foam drilling fluid. Through the methods of evaluation on the stability of foam drilling fluid, performance tests of drilling fluid and microstructure observation, the expansibility, roiling recovery rate and gas permeability test of original coal rock, the ability of micro-foam mud stabilized by nanoparticles on reducing the damage of CBM reservoir was evaluated. We found that firstly, nanoparticles can improve the stability of foam drilling fluids. Furthermore, the micro-foam mud stabilized by nanoparticles have the advantage of high-controllable density (0. 7-1.0 g/cm³) and viscosity, which can adapt to the drilling requirements of the low porosity and pressure coal seam, and which can effectively restrain the adsorption and swelling of coal rock matrix. Finally, the micro-foam mud stabilized by nanoparticles can effectively plug the low porosity and permeability coal seam, while the gas permeability recovery rate of coal is as high as 72% -96% after slice processing for the surface of pollution section of coal rock. With the integrative consideration, the micro-foam mud stabilized by nanoparticles can not only protect coal seam stability, but reduce the reservoir damage of coalbed methane, and is suitable for the low porosity and low pressure coalbed methane reservoirs drilling. [ABSTRACT FROM AUTHOR]

The existing design methods of strip coal pillar are conservative. Therefore a more rational and effective design method of strip coal pillar is needed to improve the coal recovery rate. Based on the unified strength theory (UST),a formula of limit strength for strip coal pillar was derived, which can take intermediate principal stress into account rationally. Then, analytical solutions of yielding width and remained width for strip coal pillar were presented and compared with the extended results of Wilson formula and generalized SMP criterion. Finally, parametric studies were discussed. The results show that the unified formula of limit strength, yielding width and remained width for strip coal pillar obtained in this paper is a series of results and has very broad theoretical values; the effects of intermediate principal stress and strength parameters (cohesion and inner friction angle) of coal seam on the strip coal pillar design are significant and should be fully considered; the result of Wilson formula is too conservative and the result of generalized SMP criterion is a linear approximation of the unified formula. [ABSTRACT FROM AUTHOR]

A mathematical model of thermal reversal oxidation of the low concentration methane was established in this paper. The computational fluid dynamics method was used to simulate the temperature distribution and methane concentration distribution under various operating parameters. The calculated values of methane conversion showed good agreement with the corresponding available experimental data. The model was used to investigate the effects of operational conditions such as the approach velocity and equivalence ratio on the oxidation of methane. The results show that the temperature distribution within the bed is substantially M-typed;the high temperature zone and the methane concentration distribution curve along the direction of gas flow move periodically; the greater the inlet methane concentration, the higher the temperature peak, the closer to the inlet end of the temperature curve and the wider the high-temperature region; if the premixed methane gas flow rate increases from 0. 15 m/s to 0. 70 m/s,the maximum temperature peak and the high temperature zone change little, because as the gas flow velocity increases, both the heat releasing in the reaction bed and the heat carried out by the flow increase. [ABSTRACT FROM AUTHOR]

In order to ensure strata movement control effect by solid filling mining, by combining the theory, experiment and practice, quality influence factors and strata movement control mechanism were analysed by fully mechanized solid backfilling. From the aspects of strata movement control theory, filling quality design, filling quality control and filling quality monitoring, solid backfilling quality control system framework was put forward in this paper, at the same time, the key technology was studied in detail which contained the relation between coal volume and filling, dynamic compaction and backfilling quality monitoring system. The quantitative model and the formula of the dynamic compaction were established. The underground solid filling quality monitoring system was built. Finally,the backfilling quality control system framework was put into using Pingdingshan twelve coal mine engineering practice, which can obtain the good engineering effects. [ABSTRACT FROM AUTHOR]

Based on the analysis of field observation, drilling data and geophysical data, this paper interpreted the structural deformation characteristics of Lower Yangtze region and its preservation potential for shale gas. The results show that the deformation characteristics of Lower Yangtze region vary in different areas. The structural style is not only different from south to north, but also from east to west. To the east of Maoshan, the structure style is mainly controlled by decollement folding, which was caused by the Indosinian-Yanshan movement. The following extension and reversion movements greatly are destroyed the previous structures. So it still has good shale gas preservation conditions for shale gas and not very hard to explore. The west Maoshan region, however, is strongly reworked by strong reverse and tension movements since the Indosian-Yanshan movement, and as a result a serious of extensional and faulted basins and volcanic basins were formed, which are very negative for the shale gas preservation and explorations. [ABSTRACT FROM AUTHOR]

The characteristics of late tectonic activities were studied in this paper through the field geological investigation in Wuhu area. Combining with the analysis of the regional tectonic evolution, the authors propose that the later tectonic activities which had important influence on the Paleozoic strata are divided into compressive nappe structure at Indo-China period and extensional structure at Yanshan and Himalayan period. Furthermore, the study reveals the tectonic migration regularity and that the shale gas preservation of Paleozoic strata in Wuhu area was less affected by the thrust nappe tectonics of Indo-Chinese movement, while dominated by the extension tectonics of Yanshan and Himalayan movement. This cognition about the influence of late tectonic activities should be considered in the exploration of shale gas. [ABSTRACT FROM AUTHOR]

Aiming at the current status of coal mining problems in China, this paper put forward the concept and connotation of "scientific coal mining" and "sustainable capacity of coal mining". Scientific coal mining is to maximally obtain natural resources on the premise of the harmonized geology and ecological environment under the guidance of outlook of scientific development, and to achieve sustainable mining with safety, high efficiency, green, economy and social harmony on the premise that hazards posed by complicated geological conditions and engineering circumstances were controlled; sustainable capacity of coal mining refers to the maximal coal mining capacity using safe, high-efficient and environment-friendly method on the premise that the reserves for sustainable mining within certain period were guaranteed, mainly including three requirements; safe mining, green mining and high-efficient mining. Accordingly, innovatively proposed the assessment index system and standards of the sustainable capacity of coal mining which are comprised of mining safety level, green level and mechanization level and makes comparative analysis of the current sustainable capacities of coal mining of the five coal production areas in China, the whole China and the advanced coal mining countries in the world. The results show that the coal mining capacity in 2010 scores 42.58 on average, and the coal output which complies with the standards of the sustainable capacity of coal mining and scores over 70 is about 1.078 billion tons, accounting for only 33.27% of the overall coal output; while the sustainable capacities of coal mining of the advanced coal mining countries like the United States of America, Australia, Britain and Germany score over 90. There is still a big gap between the coal mining in China and that in the advanced coal mining countries in the world, so China should extensively disseminate the idea of scientific coal mining and sustainable capacity of coal mining, insist on scientific coal mining, and raise the scientific level of coal mining in an all-round manner. [ABSTRACT FROM AUTHOR]

Based on the Kaiping coalfield gas geology research, using the method of hierarchical tectonic control theory, this paper systematically researched control action of different levels of tectonic activity on gas occurrence of kaiping coalfield. The results show that except coals with once coal generation process in NW part of Kaiping syncline, coals go through twice coal generation processes in other parts, because of the influences of thrust nappe structure and magmatic intrusion. Tectonic development inhomogeneity of Kaiping leads to coal the difference of gas occurrence. Due to the sealing role of reverse faults and water, there are good gas storage conditions in NW part, while gas loses too much in SE part because of the dissipation role of normal faults and water. Different tectonic evolution and tectonic types have different effects on coal heterogeneity. With different coal metamorphic grade and deformation characteristics in the local, there are different pore-fracture features, which leads to different gas-bearing properties. [ABSTRACT FROM AUTHOR]

To reflect the effect of confining pressure on the brittleness of the post-peak rock, the degradation angle of post-peak strength of the new parameter was presented. Based on the test data for mudstone of Shanxi in triaxial compression, the linear relationship between the degradation angle and the confining stress was founded. The law between the equivalent plastic shear strain and the degradation angle was presented, and the strain softening model of rock based on the degradation angle was set up. Fish function method within FLAC was used and the numerical code was developed. In numerical case study, the strain softening processes under variable confining pressure for mudstone of Shanxi were modeled. The simulating results accord with experimental data. Those show that the degradation angle is an effective parameter to reflect the effect of confining pressure on the brittleness of the post-peak rock; the model in this paper is reasonable and can be used to model the strain softening processes of post-peak strength rock. [ABSTRACT FROM AUTHOR]