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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]

Under the influence of open-pit mine stripping and internal backfill,there is a significant difference between the roof structure, overburden rock activity law and mining press show rule in longwall mining face of open-pit slope mine,which is different from the conventional formation condition working face. Therefore, calculation method of roof pressure also needs to be studied theoretically and experimentally according to the special roof overburden structure characteristics and stress field environment of the open-pit mine slope coal. The west side slope and south side slope coal seam in heidaigou open pit No.1 mining area is research background. The characteristics of the side slope coal seam roof overburden structure are analyzed. The coal seam at the low open-pit bench is internal backfill, and the stripping is more.This thinner and lower strength bedrock roof is covered with massive loose dumping.There is essentially no key stratum in the roof of the thick loose overburden of the weak thin bedrock. The weak thin bedrock under the bench of open-pit mine only provides a limited protective effect as immediate roof of longwall mining face.The crushing of weak the thin bedrock is also more serious because of the thick loose dumping loading.According to the traditional underground pressure theory,the roof pressure calculation of the thick loose overburden of the weak thin bedrock with no key stratum should be calculated according to the weight of all rock stratum above the support.However, according to the experimental results of similar materials, the actual pressure of the support is much smaller than the weight of the rock stratum above it.Experiments show that some protective structures still exist in roof strata with no key stratum.Based on the experimental observation and the analysis of underground pressure theory, combined with drawing theory, a hybrid model of the thick loose overburden of weak thin bedrock is proposed. The model is composed of the ellipsoid arch structure and the self-stability of immediate roof.In the open-pit mine slope coal, there are also another with no internal backfill roof overburden types of thin bedrock without overburden.For this roof overburden type,a hybrid model of thin bedrock without overburden is proposed. The model is composed of step cantilever beam structure and the selfstability of immediate roof.This paper summarizes the types of three roof overburden in the open-pit slope coal,and deduces and establishes an analytical formula for calculation method of roof pressure under the condition of three roof structures in longwall mining face of open-pit slope mine. According to the hybrid model of the thick loose overburden of weak thin bedrock,that is, the roof pressure calculated by the hybrid mechanical model combining ellipsoid arch structure and the self-stability of immediate roof is consistent with the result of similar materials experiment.Considering the self-stability of immediate roof of the calculation of the roof pressure than the traditional do not consider the self-stability of immediate roof of the roof pressure is about 14% less. Using experimental and theoretical analysis methods, the problem of ground pressure, such as roof caving,overburden strata movement,roof pressure calculation and so on, is systematically studied in longwall mining face mining process of open-pit slope mine. [ABSTRACT FROM AUTHOR]

Aimed at the challenges, such as long overhanging top-coal, poor cavability, low recovery and incoordination of coal cutting and coal drawing,faced in longwall top coal caving( LTCC) mining with extra-thick and hard coal seam in Yushen mining area, the authors discussed the feasibility and necessity of LTCC operation with super-large cutting height( greater than 6.0 m), and analyzed the coupling between hydraulic roof support and surrounding rock. Based on the coupling of strength, stiffness and stability of support-surrounding rock, a structure coupling theory of support-surrounding rock in LTCC mining with super-large mining height is put forward. The concepts and theories of "small structure" primary coupling, active supporting, and "large structure"secondary coupling,passive bearing,in the support system of hydraulic supports and the surrounding rock are explained from the perspective of the interaction mechanism between them.The authors analyzed the influence of "large and small structure"coupling of surrounding rock on the supporting effect and adaptability. It is pointed out that the structural design of hydraulic support used in LTCC not only needs to meet the requirement of adaptation of small structure supporting system to the strong dynamic load caused by periodic failure and instability of large structure, but also needs to consider the influence of the structure of hydraulic support( especially the structure of coal drawing mechanism) on the caving and migration law of hard topcoal,as well as the load evolution process of the support. The coupling between the structure of hydraulic support and the structure of caved top-coal can realize a smooth drawing of top coal and improve the recovery rate of top-coal.The methods of theoretical analysis, similarity simulation, numerical simulation and field investigation are adopted to analyze the caving and drawing structure of hard top coal and the arching effect during the coal drawing process. The influence of the structure height of hydraulic support on the caving structure and resource recovery rate of the top coal is discussed. The effect of caving mechanism structure on the arch structure of top coal and the secondary crushing effect of caving mechanism structure on top coal are studied. The structural improvement and optimization strategies of the strong coal drawing mechanism are put forward, and the mechanism and effect of coal breaking are discussed. This paper would provide guidance and reference for the coupling theory of hydraulic roof support and surrounding rock in similar hard and extremely thick coal seam. [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]

Vegetation distributed in arid and semi-arid regions, due to insufficient precipitation to maintain long-term survival, requires groundwater to provide part or all of its water demand, and thus is phreatophyte. When the underground mining destroys the aquifer, the groundwater level will drop significantly, which will cause water stress to phreatophyte, and control the ecosystem evolution process. In this paper, the authors investigated the basic characteristics of groundwater level change caused by coal seam mining in Yushen mining area, and proposed a method to determine groundwater level threshold under ecological constraints in mining area. As long as the roots are in contact with the groundwater capillary rise zone, the groundwater can be utilized by plants. Therefore, the sum of the maximum capillary rise height and the root length is regarded as the maximum critical depth of the groundwater. Under the guidance of capillary flow theory, the formula to calculate maximum capillary rise height is established by the relationship between particle arrangement and pore diameter, and the method of determining the maximum capillary rise height by particle gradation curve is given. According to the calculation, the maximum capillary rise height of the Mu Us aeolian sand is 0.7-2.0 m and the lower limit of the water level under the ecological constraints in the mine area is 4.0 m. Based on the groundwater flow field in 2016, the Yushen mining area is divided into ecologically restricted areas and unconstrained areas with a water depth of 4.0 m. Vegetation with a water depth of less than 4.0 m is highly dependent on groundwater and belongs to the ecological confinement zone. The decline of groundwater level caused by coal seam mining is very likely to cause water stress on vegetation, which is the focus of ecological environment protection in mining areas. This illuminates the limitations of ecology and water level on coal mining in Yushen mining area, which lays a theoretical foundation for further promoting water-preserved coal mining technology. [ABSTRACT FROM AUTHOR]

The stability of sandwiched water-resisting strata plays a significant role in the closed multiple-seam mining. The upper accumulated water in the upper gobs can seeped and flow into the lower mining space once the stability of sandwiched water-resisting strata is destroyed. In some situations, a sudden release of upper accumulated water is occurred, which brings serious threats for the safe mining of lower coal seam. The basic concept of water-resisting control strata under the influence of multiple mining was proposed in this paper. The damage parameter（D）calculation model of interbuRDen was established based on theories of damage mechanics. The relationships between the damage parameters（D）and the compressive strength/the damage range of interbuRDen were analyzed, respectively. Then, the influence of multiple mining damage on the stability of water-resisting control strata was investigated. The results showed that（1）The water-resisting control strata referred to the strata which did not broken under the multiple mining influences and played a significant role in preventing the downwaRD seepage and expansion of accumulated water in the upper gobs. （2）The damage parameter（D）could be used to measure the damage range of interbuRDen under multiple mining influences. （3）The relationship between the compressive strength （RD） of the interbuRDen and the damage parameter（D）was:RDof the interbuRDen showed a linear decreasing trend with the increasing of D. The reduction factor was 1-D. （4）The maximum failure depth/height(Hmax)and the maximum distance to the working face (Lmax) increased with the increase of damage parameter（D）. The larger the damage parameter（D）, the greater the increase of Hmax and Lmax. （5）The stability of water-resisting control strata was closely related with the superimposed damage induced by the multiple mining. It was necessary to comprehensively evaluate the damage range of interbuRDen under the multiple mining of upper and lower coal seams. The stability of water-resisting control strata under six different conditions were determined and the reasonable control measures were then complemented to ensure the safety of lower coal seam mining. The study on the influence of multiple mining damage on the stability of water-resisting control strata can provide a theoretical guidance for the safe mining of lower coal seam under the water accumulation area. [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]

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]

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]

In order to solve the outstanding problems faced by the coal mining, the key core technologies of the future development direction and the urgent breakthrough of the coal mining are found, the domestic and foreign energy structure and the coal status are analyzed. It is pointed out that using the scientific and technological progress to realize the safe and efficient green mining and clean and efficient utilization is the development direction of the coal, and the development of intelligent coal mine is an inevitable choice for the development of the coal industry. The connotation of intelligent coal mine and three basic theoretical problems and research directions are put forward:(1) the unified expression of multi-source and heterogeneous data and the information dynamic correlation relationship in digital coalmine;(2) the mechanism of complex surrounding rock environment-mining system and the theoretical basis of intelligent control of the whole path and attitude of equipment group;(3) the system health condition prediction and maintenance decision-making mechanism of mine equipment group. Eight operational management platforms of intelligent MOS multi-system integrated management, underground robot cooperative intelligence and feed management, underground precise positioning and navigation and 5 G communication management, geological and mine mining and transportation information dynamic management, video enhancement and real-time data-driven 3 D scene reproduction remote intervention, environment and hazard perception and security early warning system management, systematic management of intelligent unmanned working face and the health management of the whole mine equipment and facilities are conceived. The functions, characteristics and key problems of each platform are analyzed, and the corresponding construction paths and methods are put forward. By analyzing the composition and construction target of intelligent coal mine, the paper puts forward eight key technology short-boards and key technologies that need to be broken in intelligent mining, and puts forward the measures to promote the development in the aspects of both technology and management. At the technical level, there are three main directions: data acquisition and utilization, intelligent decision making and equipment R & D. At the management level, scientific production capacity layout, specialized operation service and the establishment of new standard rules and regulations system are put forward. The development goal and realization path of intelligent coal mine and intelligent mining technology are pointed out. [ABSTRACT FROM AUTHOR]

The rib spalling is a technical problem to be solved urgently in steeply dipping thick seam mining. Based on the geological conditions and characteristics of strata behaviors at No. 25221 working face in 2130 Coal Mine, the load and instability characteristics of coal wall is investigated by theoretical analysis, numerical simulation, physical analogue material simulation, and field monitoring. Results show that the asymmetry characteristics of mining pressure and strata behavior of large mining height face is higher than that of general mining height face in steeply dipping seam, which is due to mining height increase. Because the inhomogeneous characteristics of the overburden filling are further enhanced, the asymmetric characteristics of the supporting pressure of the coal wall are also obviously increased. During the process of mining, the mechanical properties of coal wall will gradually deteriorate, coal wall crazes and slip body appears. Then the slip body slides along the slip surface, rib spalling emerges, when the surrounding constraints of slip body are relieved or support pressure increases. In inclination direction, the central area is the high incidence area of rib spalling, upper secondary and lower minimum, which is consistent with the asymmetric loading characteristics of coal wall. Besides, in vertical direction, the displacement at the upper part of coal wall is larger than that at the lower part, and rib spalling is easy to occur near the roof area. And under the influence of the gravity tendency component of coal wall, the rib spalling is easy to spread to the upside. On the basis of safety production demands at No. 25221 working face in 2130 Coal Mine, some control measures have been proposed in the paper. [ABSTRACT FROM AUTHOR]