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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]

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]

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]

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]

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]

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]