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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]

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]

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]

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]