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The destruction of shallow aquifers by water-conducting fractures of overlying strata caused by underground coal mining is the most representative form of mining-induced damage in the Yushenfu mining area. It has become an important factor restricting the green mining of coal in the Yushenfu mining area and even the ecological protection and high-quality development of the middle reaches of the Yellow River. As the key scientific problem of water-preserved coal mining, the scientific understanding of the development law and main influencing factors of water-conducting fractures in overlying strata has attracted great attention. Taking the geological occurrence characteristics of the main coal seam in Yushenfu mining area as the prototype, 24 different types of numerical models are constructed with the key characteristics of the overburden structure, such as the number of layers of sandstone in the overburden (sand layer coefficient) and the thickness ratio of sandstone and mudstone in the overburden (sand–mud ratio), as the main variables. By means of numerical simulation experiment and theoretical calculation, combined with field measurement and comparison, the influence of the key characteristics of overburden structure on the development height of water-conducting fracture is studied and revealed. It is proposed that the effective area for the study area to achieve water-preserved coal mining by using the height-limited mining method must conform to the coal seam overburden structure characteristics of "sand–mud ratio 6:4 and sand layer coefficient less than 70%" and "sand–mud ratio 8:2 and sand layer coefficient less than 80%". The results not only enrich and deepen the research on the influence of geological factors and the law of controlling the development of water-flowing fractures in overlying strata, but also provide theoretical support for the precise protection of groundwater resources in the Yushenfu mining area in the middle reaches of the Yellow River. [ABSTRACT FROM AUTHOR]

The destruction of shallow aquifers by water-conducting fractures of overlying strata caused by underground coal mining is the most representative form of mining-induced damage in the Yushenfu mining area. It has become an important factor restricting the green mining of coal in the Yushenfu mining area and even the ecological protection and high-quality development of the middle reaches of the Yellow River. As the key scientific problem of water-preserved coal mining, the scientific understanding of the development law and main influencing factors of water-conducting fractures in overlying strata has attracted great attention. Taking the geological occurrence characteristics of the main coal seam in Yushenfu mining area as the prototype, 24 different types of numerical models are constructed with the key characteristics of the overburden structure, such as the number of layers of sandstone in the overburden (sand layer coefficient) and the thickness ratio of sandstone and mudstone in the overburden (sand–mud ratio), as the main variables. By means of numerical simulation experiment and theoretical calculation, combined with field measurement and comparison, the influence of the key characteristics of overburden structure on the development height of water-conducting fracture is studied and revealed. It is proposed that the effective area for the study area to achieve water-preserved coal mining by using the height-limited mining method must conform to the coal seam overburden structure characteristics of “sand–mud ratio 6:4 and sand layer coefficient less than 70%” and “sand–mud ratio 8:2 and sand layer coefficient less than 80%”. The results not only enrich and deepen the research on the influence of geological factors and the law of controlling the development of water-flowing fractures in overlying strata, but also provide theoretical support for the precise protection of groundwater resources in the Yushenfu mining area in the middle reaches of the Yellow River.

Water-preserved coal mining (WPCM) in water-shortage mining areas is an important aspect of water resources management. This paper aimed at the protection of Cretaceous groundwater resources during the high-intensity mining in the Yonglong mining area, China, and carried out basic theory and practical application of WPCM. The hydrogeological structure and engineering geological characteristics were investigated on-site. On-site detection and numerical simulation were used to study the dynamic evolution laws of overburden failure and water-conducting fractured zone (WCFZ), and the seepage laws of mining-induced overburden were analyzed by the rock triaxial seepage test. The results showed that it was feasible to carry out WPCM in the Yonglong mining area. From the view of reducing the height of WCFZ and preventing water hazards, the technical measures for WPCM were proposed. The research results can provide a theoretical basis and technical approach for WPCM in the water-shortage mining areas. HIGHLIGHTS The feasibility of water-preserved coal mining was analyzed.; Overburden failure and seepage laws induced by coal mining were studied.; Water-preserved coal mining technologies were proposed.;

With abundant mineral resources, many types of mining industry and many mines, mining development in China has led to the decline of groundwater level around the mines, waste of water resources, water quality pollution, surface collapse, land degradation, reduction of vegetation cover, and different degrees of impact on groundwater resources and ecological environment. In order to solve the problems of water waste and ecological damage caused by the lateral recharge of water from the strong seepage loose layer to the mine pit, we proposed a vertical curtain water interception technology with flexible magnetic suction membrane to protect the groundwater resources and ecological environment of coal mines. We firstly studied the performance of the suction membrane material, developed the magnetic absorption suction membrane connection process, and carried out indoor tests of different suction membrane connection processes, then we conducted a 1 369 m strong seepage loose layer water interception curtain field test application in the test mine. The research results show that the impermeable membrane has low permeability coefficient, dense structure, high flexibility, resistance to deformation and durability, and is a good material for water cut, pollution control and seepage control, which can meet the requirements of vertical curtain for the strong seepage loose layer of the mine. The self-developed magnetic suction joint material and connection process solved the problems of shallow laying depth, joint leakage and complicated operation of existing connection processes such as overlapping lap, joint lock and joint box, etc. The construction depth of suction membrane curtain connected by magnetic suction joint is not limited by the connection conditions, and the water interception effect of magnetic suction joint connection process is better than that of overlapping lap and joint lock (joint box) connection process. Through the test of making, laying, connecting and backfilling the curtain into a wall with 2 kinds of flexible magnetic absorbent impermeable membranes, the gap at the joint of the impermeable membrane was reduced from 5-20 cm to 0, and the two adjacent impermeable membranes were closely connected as an organic whole, which reduced the water passage of the interception curtain at the joint. Through the mine-field site test, it was found that the water catchment pits below the curtain which had been filled with strong seepage loose layer water leakage for a long time, had dried up, and the water level of strong seepage loose layer outside the curtain had increased by 5.55-9.12 m, and the water level inside the curtain had decreased by 3.21-5.84 m, so the protection of strong seepage loose layer water resources had achieved good results.

Underground water storage in goaf is one of the important means of water conservation and mining in the western ecologically fragile area. The stability of waterproof sealing wall is related to the safety of water storage in goaf. In view of the key problem that the stability of the waterproof sealing wall in the goaf is difficult to monitor and the water pressure resistance ability is difficult to predict, under the background of underground mining end sealing in Chahasu Coal Mine, by means of theoretical analysis, numerical simulation and field measurement, the mechanical properties of coal seam and roof and floor are tested, and the minimum compressive strength of coal body and roof and floor is obtained. Considering the stress characteristics of the sealing wall structure, the maximum bearing capacity of the waterproof closed wall without the influence of mining is calculated and deduced. The numerical model of waterproof sealing wall is established, and the stress state, deformation and damage of sealing wall under the influence of advanced mining and different water head heights (6, 9, 12 and 15 m) were analyzed. The stress and displacement monitoring systems of the waterproof sealing wall in the underground goaf has been developed. Based on the theoretical analysis, the monitoring points had been reasonably arranged and applied in the field. On this basis, combined with theoretical analysis and numerical simulation results, the maximum safe head height of the waterproof sealing wall and the head height of the warning water line are determined. The results showed that the advance mining has a certain impact on the damage of the waterproof sealing wall, and the water pressure increases the sliding range of the cracks between the sealing wall and the coal pillar contact surface. The maximum water head height borne by the waterproof sealing wall at the end of mining is 12 m, and the water head height of the warning water level line of the waterproof sealing wall is 9.6 m. The contact surface between the wall and the coal pillar as well as the top and bottom corners of the closed wall are structural weak surfaces, which are prone to damage. Attention should be paid to strengthening the monitoring or observation of the position of the sealing wall embedded in the coal and rock mass and the top and bottom corners of the sealing wall. If necessary, grouting and plugging can be used to reinforce the weak surface or leakage part of the structure. The research results can provide theoretical basis and application reference for stability monitoring and water pressure resistance evaluation of similar mine waterproof sealing walls.

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Short-wall block backfill mining (SBBM) technology can effectively solve the problems of coal resources waste, water resources loss and gangue waste accumulation. However, after the long-term effect of mine water, the internal heavy metal ions in the gangue backfill materials may be leached, which have a certain potential impact on the groundwater environment in the mining area. Therefore, according to the technical characteristics of SBBM technology, comprehensive prevention of water resources loss and water resources pollution during SBBM was studied systematically. First, prevention and control of water resources loss in the mining area. Based on the combination relationship of “coal pillar, backfill body-barrier layer-aquifuge”, The development of water-conducting fractures in overlying strata under SBBM were analysed. The control mechanism of water resources protection under the evolution of overlying strata structure induced during SBBM was revealed. Secondly, prevention and control of water resources pollution in mining areas. The migration model of heavy metal ions in the gob was established. Then, the pollution mechanism of gangue backfill materials to water resources was revealed, the migration law of heavy metal ions in gangue backfill materials was analyzed, the comprehensive prevention and control technology of water resources destruction in mining area was summarized, the comprehensive prevention and control technology of water resources loss-pollution in mining area was summarized, and the design method of filling ratio based on water resources loss-pollution prevention was put forward. The results show that the gangue materials were filled into the gob as the backfill body, the gangue materials would be the permanent bearing body, which bore the load of the overlying strata accompanied with the protective coal pillar among the blocks, which could greatly prevents the collapse of the low-level stratum, restrict the water-conducting fractures to penetrate the barrier layer and protect the integrity of the high-level stratum. In addition, the heavy metal ions in gangue backfill materials were subjected to the coupled action of seepage, concentration, and stress and then driven by water head pressure and gravitational potential energy to migrate along the side of the coal pillar and below the floor stratum, during which mine water served as the carrier. The migration distance of heavy metal ions increased with increasing of the permeability of floor strata, leaching concentration of heavy metal ions/pollution source intensity, depth of floor breaks and water level heights, and decreases with the increase of gangue particle size and surrounding rock stress. Based on this, the comprehensive prevention and control technology of water resources loss-pollution in mining area was summarized, it included mining parameter control technology, backfill parameter control technology, pollution source control technology, transmission route control technology and in-situ water control technology. and the design method of filling ratio based on water resource loss-pollution prevention and control was put forward, which can realize the comprehensive prevention and control of water resource loss-pollution in mining area. This study will provide scientific theoretical basis and guidance for the comprehensive prevention and control of the water resources destruction problems caused by coal mining.

The shallow groundwater of the Quaternary Salawusu Formation in China is distributed widely in the arid and semi-arid areas of northern Shaanxi and is an essential component of water supply and ecosystem maintenance there. To safely exploit the coal resources and protect the water resources, it is important to understand the impact of local high-intensity coal mining on such shallow groundwater. We used the "three maps—two predictions" method, the theory of equivalent mining height, and numerical simulations to evaluate the water inrush conditions for the 3–1 coal seam and to analyze the feasibility of backfill mining under the Qingcaojiegou and Hezegou Rivers. The results for the Jinjie coal mine showed that: part of the Quaternary porous phreatic aquifer and most of the J2z weathered-bedrock pore–fissure confined aquifer are high-risk areas in the connectivity zoning map; there are large areas of strong or relatively strong water-abundant areas in the 3–1 coal seam roof, and; large areas in the southwest, northwest, and northeast parts of the coalfield are in high- and low-risk areas and face a serious threat of roof water inrush. Overall, it should be feasible to mine under these rivers, using backfill mining to effectively reduce the height of the water-flowing fractured zone and amount of surface subsidence. [ABSTRACT FROM AUTHOR]

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The application of water resources protection mining has alleviated greatly the deterioration of ecological environment in the ecologically fragile mining areas of Western China. To quantitatively evaluate the improvement effect of this technology on the ecological environment of the mining area, the evaluation index system of ecological environment in the mining area was proposed based on the water-preserved mining techniques of water resources protection mining. The entropy weight method and the Decision-making Trial and Evaluation Laboratory were selected as the subjective and objective weight method, and the cloud model theory was used as the modeling basis, then a quantitative evaluation model of ecological environment of water-preserved mining was constructed. Besides, the Halagou coal mine in Shendong Group was taken as an example, and the ecological environment of this mining area was quantitatively assessed to verify the rationality of the proposed evaluation model. The results show that the ecological environment level of the Halagou mining area is between Excellent and Good (generally at a good level), which is consistent with the actual ecological environment situation of the Halagou mining area. Thus, the rationality of the proposed evaluation model is verified. Through the evaluation cloud map, the evaluation results are biased towards the evaluation level of Good, indicating that there is still room for improvement in the ecological environment of the Halagou coal mine. Combined with the analysis results, suggestions for the sustainable improvement of the ecological environment of the mining area are given: Halagou coal mine should focus on the restoration of subsidence area and the control of mine water inflow.

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Strata movement control during coal seam's backfill mining is very much related to the mechanical properties of backfill body in goaf. A mechanical model of the structural water-resistant strata (SWRS) of stope overburden in backfill water-preserved mining (BWPM) was established on the basis of the key strata theory in ground control. This approach was conducted to investigate the mechanical properties of backfill body on the overburden water-resistant strata stability. The proposed model was based on the compressive mechanical properties of the filled gangue, which considered the linear and nonlinear elastic mechanical properties of backfill body. The stability mechanics criterion of the SWRS of stope overburden in BWPM on the nonlinear elastic foundation was deduced by introducing the tensile yield criterion. The maximum tensile stress (MTS) that acts on the SWRS of stope overburden decreased with the increase of the backfill body's linear elastic foundation coefficient of k1 and the nonlinear elastic foundation coefficients of k2 and k3. However, the MTS rapidly decreased with the increase of k1 and slowly decreased with the increase of k2 and k3. The sensitivity analysis indicated that k1 exhibited the greatest effect on the MTS that acts on the SWRS, thereby accounting for 72.38%. In addition, k2 and k3 showed less effect on the MTS that acts on the SWRS, thereby only accounting for 19.56% and 8.06%, respectively. Results showed that the backfill body's linear elastic foundation coefficient plays a very important role in controlling the stability of the SWRS of stope overburden in BWPM. Increasing k1 is more beneficial to the stability control of the water-resistant strata of stope overburden than increasing k2 and k3, especially the latter. [ABSTRACT FROM AUTHOR]

The Jurassic coalfield in northern Shaanxi, China is one of the seven largest coalfields in the world. It is located in an arid region of northwestern China, with poor water resources and fragile ecological environment. Due to coal mining, the rock layers on the coal seam will be slumped and fractured to produce fissures. The penetrated fissures will cause a mine water burst disaster and cause damage to groundwater and surface water. The strip filling method can control the expansion of the diversion fissure zone and protect the groundwater and surface water from the underground mining of coal. In this paper, the effects of different strip filling conditions on the diversion fissure zone are studied by discrete element numerical experiments. The study indicates that the upward-fissure and the downward-fissure penetrations are the direct causes of the instability of the water-blocking rock group. After the upward fissure extends to a certain extent, there will be a downward fissure. Under the condition of controlling the width of the filling strip and the compressive strength, the strip filling method can effectively prevent the upward and downward fissures of the water-blocking rock group from penetrating and can ensure that the surface water system is not affected by the underground coal mining activities. [ABSTRACT FROM AUTHOR]

China has a long history of coal mining. The mining method has gradually changed from the room-pillar mining to the full-mechanized mining. Based on Dabianyao coal mine and Liangshuijing coal mine in China, this article takes the ground subsidence induced by different mining methods as the object of study. Through field investigation and analysis of the basin area, the ground subsidence in the basin is divided into the sudden subsidence of room-pillar mining and the predicted subsidence of underground full-mechanized mining. This paper expounds and summarizes the characteristics of ground fissures and subsidence troughs which are the main manifestations of surface subsidence in the basin. On the basis of disaster investigation, investigators also investigate the land resources, springs, wells and surface water in the basin. The results show that the ground subsidence has serious influence on the geological environment. The topography and physiognomy are changed by the ground subsidence. The land resource has been destroyed. Groundwater leaks and water level drops, and the surface water also flows along with ground fissures. Many springs in this area have dried up, and branch ditches have been cut off. [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]

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To better understand the physical and mechanical behavior of weakly cemented rock with different moisture contents for the success of water-preserved mining, this paper presents the systematic tri-axial compression tests on three typical rock samples (i.e., mudstone, sandstone, and sandy mudstone) sampled from Ili mining area, where the environmental requirements for water conservation are significantly strict. Both the influences of moisture content and confining pressure on the failure mode and the stress-strain behavior of weakly cemented rock have been discussed and compared with each other. Test results showed that: (1) compared to sandstone and sandy mudstone, both the peak stress and residual stress of the weakly cemented mudstone are much more sensitive to confining pressure and moisture content. In detail, the peak stress is very relevant to moisture content, whereas, the residual stress is more sensitive to the confining pressure, (2) with the increase of moisture content, both the yield and ductility of weakly cemented mudstone have been significantly enhanced. However, a similar experimental observation has been found for sandstone and sandy mudstone, and (3) the microstructure and the mineral component are believed to be the two main factors leading to the scatter in terms of the stress-strain behavior for different weakly cemented rocks. Experimental results and discussions presented in this paper can provide the guideline for further research on the application of water-preserved mining in other coal mines with a similar geological condition.

In view of the problems such as the shortage of filling time and filling space,the difficulty of coordination between coal mining and filling operation and so on,the new method named “backfilling while mining” was applied to water-preserved mining.In the mining of process,all the roadway in the mining block is divided into several mining stages.The work on the roadway's mining and filling in the next stage begin when the previous stage’s work are finished.With the work on all the roadway's mining and filling finished,the filling body will substitute coal absolutely.For the purpose of the roadway's sides being solid coal or filling body reaching the designed strength,the roadway should be excavated alternately.The research results are applied to Wangtaipu coal mine.Field practice shows that under the condition of the mining rate of the whole block reaching 96.8%,and the surface deformation is less than the Grade I damage index,the shallow water resources will be preserved effectively.The method applies the mining pattern of “backfilling while mining” so it can realize the advantage of fast continuous mining and backfilling mining and achieve the work on water-preserved mining. [ABSTRACT FROM AUTHOR]

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present paper is to study the relationship between vegetation and groundwater, and the constrains on coal mining in ecologically fragile mining area. A field survey was carried out to determine the general rules of vegetation community succession, along with the increase of depth to groundwater table (DGT) in a typical region. Based on the remote sensing data and DGT data before mining, a statistical relationship between the normalized difference vegetation index (NDVI) and DGT was established in Yushenfu coal mining area. The results showed that the vegetation has a zonal characteristic as DGT increasing,and the most suitable DGT for vegetation is 0-4.0 m, the smaller the DGT, the more sensitive the vegetation. Combined with the hydrological condition and the relationship between vegetation and groundwater, the Yushenfu coal mining area could be divided into three parts: vegetation constraint region, groundwater constraint region and non-constrained region. It is in the vegetation constraint region that coal mining will cause extensive damage to vegetation. As the DGT dramatically declined, the NDVI improved in large extent by 2014, to some extent, this was due to the present mining mainly located in non-constrained region. Mine planning and coal mining must pay attention to the relationship of vegetation and groundwater in ecologically fragile mining area. [ABSTRACT FROM AUTHOR]

The similar simulation experiment has always been an essential method to study water-preserved mining, during which the similarity between simulation materials and rock properties is the most significant issue. Ningdong coalfield is a typically ecological-fragile mining area where a special sandstone contains a large amount of low maturity and clay minerals. This sort of sandstone represents the soft-rock properties under mining influence and water absorb-drying process. It was confirmed that this is coarsely argillaceous arkose which is formed in quickly emerging sedimentary environment in accordance with its composition and structure. The sandstone is comprised of clay, quartz and feldspar by the quantified analysis of X-ray diffraction. The clay incorporates enormous mont-morillonite, illite smectite mixed layer and chlorite and all of these materials are water swelling. The study of triaxial compressive strength and permeability of the sandstone by MTS Servo demonstrates that the sandstone samples have plastic-failure characteristics. The permeability of water-saturated sandstone has mutational points, after which it is approximately constant before increasing to the maximum at failure. In addition, the uniaxial compressive strength and elastic modulus have a negative relation with moisture content. [ABSTRACT FROM AUTHOR]

The burnt rock aquifer is an important ecological water resources in Yushenfu mining area. In order to study the water loss and protection of burnt rock, this paper analyzed classification, distribution, hydraulic connection and water enrichment feature of burnt rock. Numerical simulation method was used to predict water loss which caused by mining and then concluding three approaches of “offsite storage” burnt rock water. The research shows that burnt rock can be divided into 3 categories and 5 small classes, among them sinter rock and similar lava rock are main water storage carriers. The distribution of burnt rock is controlled by topography, while the scale is affected by coal seam thickness, exposed height and spontaneous combustion conditions. Besides, water abundance of burnt rock is determined by supply condition, excretion condition and water storage condition. The result also shows the burnt rock aquifer is subjected to the recharge of the overlying aquifer and excreting by spring and mine drainage. Additionally, draining water quantity and borehole design was summarized by numerical simulation. On the basis of experience of water-preserved mining, three methods could be summarized to protect and utilize water resource of burnt rock, which are reservoir water storage, goaf water storage and surface water irrigation. [ABSTRACT FROM AUTHOR]

In order to protect the ecological phreatic level in ecologically fragile mining area, the reasonable thickness of protected loess with mining were studied. Based on groundwater dynamics, the mechanisms of phreatic level leaky with mining had been analyzed. Also, the laws of phreatic level variation with different mining residual thickness and the physical properties of loess had been analyzed by water-electric similar simulations. The results show that the more leaky head and the weaker water isolation, the smaller phreatic decline with mining. While 42.6 m loess of Lishi Group or 21.0 m loess of Baode Group, the mining phreatic level can range in the ecological phreatic level for the typical geological condition of the study area. Water-electric similar simulations of typical geological condition in mining workface is achieved by multiple software. The relationship of mining residual thickness and phreatic decline shows that water-electric simulation results are anastomosing in theoretical results. The results are preliminarily proved by engineering practice. [ABSTRACT FROM AUTHOR]

Theoretical analysis is taken on the water sediment two phase flows pattern of fractured rock based on lattice Boltzmann method and a model is built. Also, the basic conservation equations are derived and the control equations are established. The water and sand phase interface is analyzed by using the Euler point and Lagrange point based on the immersed boundary method. Numerical simulation is taken on sand inrush, and the flow patterns of sand moving in fracture is analyzed, the influence of particle size and fracture width on the velocity of sand inrush is studied. With the results in single fracture, a mechanical model of sand mining roof covered with thick loose is established to analyze water and sand inrush, the authors find that at the initial stage, the sand particles flowing in cracks can restrain its development, with the water pressure continually applied, a large number of water and sand mixture begin to flow in, which makes the pore pressure increase, causing the cracks rapidly develop, even causing the roof fall, aggravating the water and sand inrush. [ABSTRACT FROM AUTHOR]

Considering the wide-range and nonlinear characteristics of strata movement and the demand between large range and high precision in the physical simulation of water-preserved mining, a method for improving displacement measurement precision in physical modeling has been proved by experiments. The results show that the measurement accuracy is improved as the number of reference points and displacements increase. The increase of the number of reference points could reduce the system error which fluctuates in a range depending on the number of reference points and the fluctuation ascribes to the plus or minus of error. The mean error starts to reduce and diminish significantly when the number of reference points is 15 and 25 respectively. Therefore, at least 25 reference points are required to ensure the required precision. The method suggests a way for measuring strata movement in mining physical models. [ABSTRACT FROM AUTHOR]

The core idea of the shallow buried coal seams in Western China is to protect the ecological water level. The theoretical basis of the strata control in water conservation mining is the stability of the water resisting layer. According to simulation model tests and mining surface cracks observation, it reveals that the cracks of overburden strata induced by mining are mainly composed of “upwards cracks” and “downward cracks”. The water resisting property of overburden aquifer layer depends on the interpenetration of mining cracks band. The calculation formulas of the height of upward crack zone and the developing depth of downward crack zone are set up. Based on the thickness of the water resisting strata to the mining height, so-called resisting-mining thickness ratio, the water resisting criterion is established, and the classification method of water conservation mining is also put forward. Based on the overburden condition of Yushenfu mining area, the classification index range for the water conservation mining in shallow buried coal seam is suggested. [ABSTRACT FROM AUTHOR]

In terms of the problem of the lowering of water level at Yellow River ecological wetland, which is caused by water inrush into coal working face from the thin aquifuge-low confined water limestone aquifer,this paper used numerical simulation, in-situ measurement and mathematical statistics methods to analyze the development rule of the floor failure in mining,and to study the key technology of loess efficient grouting for coal seam floor based on laboratory experiments and grouting industrial experience. The results show that the mine water inrush will be reduced more than 90% by grouting de-sanding-decentralized loess slurry under the depth of floor failure, and the high intensity mining caused no further degradation in semi-arid areas. There is a remarkable ecological benefit to ecological wetland. [ABSTRACT FROM AUTHOR]

In terms of the key scientific problems in the research of basic theory on water resources protection during mining on coal seam in northwest China, this paper introduces the following research developments：the stratigraphic structural characteristics of northwest coalfield, the space-time evolution laws on the stabilities of the overlying strata structure and aquiclude, and the mechanism and control theory of water-protection coal mining. The geometrical structure model of ecology-water-coal measure rock strata was established based on different eco-geological types in northwest mining area. Distribution characteristics and water cycle migration regularity of the shallow water resources were analyzed. The expression and reconstruction method of overlying rock fracture was proposed. The coordinated variation model and the gradual variation model on the relationship among upper aquiclude, medium barrier strata and lower main roof were built. A classification system on water-protection mining technology referred to virginal/repeated mining was constructed. A new type of shortwall mining with water protection was explored. The above works lay a foundation for scientific coal mining method on water protection in northwest of China. [ABSTRACT FROM AUTHOR]

In order to solve the water inrush problems induced by mining under water bearing strata, this paper proposes the method of water protection based on solid backfill mining. Meanwhile, the fundamental principle of this method is introduced and the evolution characteristics of water-conducting fracture in solid backfill mining are analyzed. Moreover, the calculation model of critical compression ratio is established according to the predicting formula of the height of water-conducting fracture zone in solid backfill mining and the coal mining regulations and coal pillar design affected by buildings, water bodies, railways and main roadway. Then, the compression ratio of coal seam induced by mining under water bearing strata is designed, which is used for the layout of solid backfill mining panel. The engineering application results in CT101 backfill mining panel show that the average measured value of mass ratio is 1.32, which is bigger than theoretical design value and the height of water-conducting fracture zone is about 10.0 meters, indicating that this method effectively reduces the height of water-conducting fracture zone and can achieve the goal of safe mining under water bearing strata. [ABSTRACT FROM AUTHOR]

To study the safety of overlying strata by backfilling in the water preserved mining under thick alluvium and thin bedrock, the CT101 coal mining face of Wugou Colliery was chosen as the research site. By employing theoretical analysis, numerical simulation and drilling detection to analyze the stability of water-resisting key strata, revealing the destruction rule of overlying strata in working face mining with filling, and analyze the safety of mining. The results show that water-resisting key strata remains stable when the thickness of coal seam is 6 m and filling rate is 85%；the downward cracks with bridging are distributed mainly over both the ends of working face. As the working face advancing, downward crack depth periodically increases and decreases. The depth of downward crack is 5.5 m, and the height of upward crack is 6.41-11.85 m, the thickness of the aquifuge is 17.38-23.97 m, working face can be mined safely. The study provides a reference for the safety analysis on mining under similar mining conditions. [ABSTRACT FROM AUTHOR]

The ecological environment is relatively weak due to the low precipitation and high evaporation. The study area is the Dananhu mining area of Hami coal field, which is located in the Turpan-Hami basin. For the ecologically vulnerable area, the authors studied the hydro-geological conditions for water-preserved mining and its feasibility. The structure of aquiclude in the roof of major coal seam has been systematically assessed. Furthermore, the authors investigated the development characteristics of the height of the water flowing fractured zone, and studied the development potential of aquifer under protection. Then, the practical application for water-preserved mining had successfully conducted at the 1801 working face of Dananhu No.5 Coalmine as a case study. This study proposed a preliminary program for the development and utilization of protecting high salinity aquifer water, gaining experience for water-preserved mining in the ecologically vulnerable area of the Turpan-Hami Basin. This paper first put forward and practiced the roof water disaster control and water-preserved mining combining engineering in the typical ecological fragile area of Tuha Basin, providing theoretical and practical references for safely exploit the coal resources in Turpan-Hami coal field, which is one of the four major coal bases in Xinjiang Province. [ABSTRACT FROM AUTHOR]

The desert runoff area is an important water source in Yushen mining area. To protect water resource in desert,and ensure safe and efficient coal mining, the authors develop a key technology for coal mining with water contained in desert. The influence factors and the zoning standards of the coal mining with water contained are analyzed by means of field measurement and numerical calculation. The results show that：coal miming under river recharged by desert may lead to two type of water loss, i.e., flow in river and groundwater in recharge area. The recharge area is divided into water and sand inrush region, water inrush region, leakage region and water retention region. The residual thicknesses of aquifuge can be regarded as a safe indication whether the flow in river could pour into worked-out section or not. Repairing cracks in leakage area, building dam drainage in water bursting area, using the hydrodynamic conditions and controlling sand source flow technology can control in water and sand inrush area. The comprehensive treatment of mining area made a successful engineering application for the mining face across trench. [ABSTRACT FROM AUTHOR]

Shendong mining area is a China’s important coal production base and a typical high intensity mining field，which is also a typical fragile ecological environment of arid and semi-arid areas. The coordinated development of coal production and ecological environment in high intensity mining area is an important research topic in the area. Aiming at the lack of water resource in arid and semi-arid, fragile ecological environment in Shendong mining area, this paper puts forward the partition of hydrogeological structure and the water-preserved mining by studying the structure characteristics of hydrological geology, coal strata structure type, etc. On this basis, according to different hydrogeological structure types, it puts forward the key technologies of water-preserved mining such as coal mining important water source area in mining area, thick bedrock aquifer, burning rocks aquifer and thin bedrock aquifer and the use of mine water resources. Finally, combining with the typical mine, it applies the key technologies into engineering practice and achieves a good application effect. [ABSTRACT FROM AUTHOR]

It is universally acknowledged that phreatophytic transpiration changes sensitively with groundwater level declining. The present study tries to find the groundwater level decline threshold limited to the vulnerable ecological conditions at Yushen mine. The methods include in-situ test and numerical analysis, firstly an experimental base was constructed for collecting data, including meteorological factors, soil moisture, groundwater level and Salix psammophila transpiration, then a root water uptake model was derived to simulate the change of Salix psammophila transpiration during groundwater level declining. The results show that：Salix psammophila transpiration is strictly controlled by meteorological factors, there appears two extremums before and after 12 noon, and Salix psammophila transpiration changes more sharply with a shallow groundwater level. The contribution rate of groundwater to evapotranspiration declines with the groundwater depth goes deeper, which decrease from 100% to 0 with groundwater depth decreasing from 15 cm to 215 cm. Salix psammophila cannot utilize groundwater when the groundwater depth is more than 215 cm, that is the threshold of groundwater level decline limited to the vulnerable ecological conditions during coal mining in the study area. The results achieved above will enrich the coal mining technology at ecologically vulnerable coal mine. [ABSTRACT FROM AUTHOR]

Aim to find methods for aquifers and ecology protection in arid and semi-arid mines, the paper put forth the concept and the scientific connotation of water-preserved mining, and established its basic frame from systematical theory based on coal geology, mining conditions and strata movement characteristics in the Yushen mine area. Water-preserved coal mining applies to in arid and semi-arid coal mining areas. Its objective is to protect aquifer structures and base flow of rivers. Its major research contents include geological and hydrogeological conditions, rock movement control technology, constraint conditions both water and ecology, and key mining technique. Three basic ways, which are to refrain from water flowing fractures by controlling strata movement, to reconstruct aquicludes and remodel aquicludes by grouting, are widely adopted in water-preserved mining. Challenges facing are filling at high cost and negative environmental effects of shallower buried depths of water table in deserts due to land subsidence. Studies on water-preserved coal mining are theory base and evidence for coal mining and water resource protection in arid and semi-arid mines. [ABSTRACT FROM AUTHOR]

In order to study the influence of high intensity coal mining on the groundwaterlevel in Yu-shen-fu area,and analyze the relationship between phreatic decline and coal mining intensity, authors draw the groundwater level contour map in 1995 and 2014 through data collection and field investigation, then obtained the groundwater level variation and the relationship of mutual-feed joint-variation with coal mining intensity through map overlapping. The results indicate that; (1) 73.0% of regional groundwater level does not change significantly, but there are 758. 9 km2 where the groundwater level lowers more than 8 m, accounts for 7. 3% of the study area, thus it has a large impact on the regional groundwater balance. (2) The high intensity coal mining is the main driving force that causes the groundwater level decline more than 8 m ,7 1 .5% of which is concerned with mining scale. (3) Water flowing fracture zone and aquifer characteristics are two factors to control the range and degree of groundwater level variation. Coal mining with water-containing is extremely important to achieve the harmonious development of resources and environment. [ABSTRACT FROM AUTHOR]

Based on the exploitation background of gully terrain area in western China, the relationship between strata movement and groundwater level decline was established by adopting theoretical analysis and simulation methods, and then the influence of longwall mining on surface runoffs in gully terrain area was discussed. The results show that if the aquifer is not damaged by mining-induced fractures, the basin morphology and catchment area will vary due to mining subsidence, which would subsequently affect the distribution of surface runoffs and water environment. With the increasing intensity of underground mining, four types of surface runoffs distribution caused by mining in gully terrain area will appear including “stable” type, “derivative” type, “transfer” type and “deterioration” type. When mining height and mining area are relatively small, groundwater and surface water level decline is not obvious and regional water environment has minor changes. When mining height is large but mining area is small comparing to the basin area, groundwater level decline is not obvious but surface subsidence is considerable. Hence, the buried depth of groundwater level is shallower than before in mining area. When there are gullies overlaying on the surface of the mining area, groundwater may outcrop in the gully as its low elevation, from which new surface runoff would derive. As the mining area enlarges comparing to the basin area, groundwater level in the whole area obviously declines; thus the original surface runoffs outside the mining area disappear and are transferred to the mining area because of its large surface subsidence. Finally, groundwater level declines rapidly due to larger mining height and mining area. Eventually, all the surface runoffs disappear and are converted into groundwater, causing regional ecological environment deterioration. This research provides a theoretical basis for water-preserved mining practice in arid and semi-arid areas of western China. [ABSTRACT FROM AUTHOR]

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It is the unique geological environment conditions in northern Ordos Basin Jurassic coalfield that the issue “water-preserved coal mining” is presented. After years of research，there have been some significant progresses in basic research and engineering practice. This paper summarized the latest achievements in the research of water-preserved coal mining. In the basic research phase：identified spatial distribution relation between coal bed with aquifers and impermeable layer；established the structure type of coal bed roof；divided the coal mining area into different partitions to protect aquifer；and specified the mining methods in different regions to protect groundwater. In the engineering practice phase：five kinds of aquifer-structure-preserved mining methods be employed to protect roof aquifer structure，including cut-and-fill mining，strip mining，slice mining，short-wall continuous mechanical mining and fast marching mining；reinforced bottom plate by grouting to protect Karst confined water in Weibei mining area；and transferred swallet into mined-out area to improve the utilization. [ABSTRACT FROM AUTHOR]

• Establish an ecological evaluation index system based on water preserved mining. • Use DEMATEL theory to realize the relationship analysis between indicators. • Propose the subjective and objective weight method of DEMATEL-entropy method. • Cloud model is introduced to construct the eco-environment cloud evaluation model. • Verify the rationality of the cloud evaluation model through example. The application of water resources protection mining has alleviated greatly the deterioration of ecological environment in the ecologically fragile mining areas of Western China. To quantitatively evaluate the improvement effect of this technology on the ecological environment of the mining area, the evaluation index system of ecological environment in the mining area was proposed based on the water-preserved mining techniques of water resources protection mining. The entropy weight method and the Decision-making Trial and Evaluation Laboratory were selected as the subjective and objective weight method, and the cloud model theory was used as the modeling basis, then a quantitative evaluation model of ecological environment of water-preserved mining was constructed. Besides, the Halagou coal mine in Shendong Group was taken as an example, and the ecological environment of this mining area was quantitatively assessed to verify the rationality of the proposed evaluation model. The results show that the ecological environment level of the Halagou mining area is between Excellent and Good (generally at a good level), which is consistent with the actual ecological environment situation of the Halagou mining area. Thus, the rationality of the proposed evaluation model is verified. Through the evaluation cloud map, the evaluation results are biased towards the evaluation level of Good , indicating that there is still room for improvement in the ecological environment of the Halagou coal mine. Combined with the analysis results, suggestions for the sustainable improvement of the ecological environment of the mining area are given: Halagou coal mine should focus on the restoration of subsidence area and the control of mine water inflow. [ABSTRACT FROM AUTHOR]

With the adoption of lab physical simulation, this paper has studied the moving characteristics of overlying strata and the development rules of water-flowing fractured zone in multi-excavation disturbed zone in close-distance seams, and analyzed the feasibility of water-preserved mining in multi-excavation disturbed zone. The experiment result has showed that under the geological conditions of Suancigou Coal Mine, after the upper slicing mining of upper-6 coal seam, the development height of water-flowing fractured zone of underlying strata is 50.2m, and the No.3 mudstone (water-resisting layer) is kept in good condition, thus, the water-preserved mining can be adopted in this area. After the lower slicing mining of upper-6 coal seam, the development height of water-flowing fractured zone reaches to 73.4m, and the No.3 mudstone (water-resisting layer) remains intact, thus, the water-preserved mining can be achieved in this area. After the excavation of No.6 coal seam, the water-flowing fracture penetrates No.3 mudstone and connects with the aquifer of Shanxi formation of lower Permian series, causing the loss of water resources, thus, the water-preserved mining cannot be adopted in this area. Meanwhile, although the water-flowing fracture of underlying strata in the middle of gob is gradually closed under compression after excavation, the fracture development of underlying strata around the gob is difficult to be closed, especially at the vicinity of the mining terminal line where has strike advanced fracture with obvious development. Therefore, to adopt water-preserved mining in No.6 coal seam, relevant technical measures of excavation must be adopted, such as lowering the mining height, filling the surrounding areas of the gob, adopting coordinated excavation to avoid overlaps in the boundaries of the upper and lower parts of gob, and practicing strip mining or short wall mining etc. The research results provide reference for water-preserved mining in close-distance seams. [ABSTRACT FROM AUTHOR]

The success of the water-preserved mining technology is closely related to the stability of the aquiclude and the aquifer, in particular, which is made of weakly cemented rock mas. This paper starts with the tri-axial compression tests on the mudstone specimens obtained from the Ili mining area, followed by the systematic numerical simulation via the Particle Flow Code (PFC) program, aiming at obtaining an in-depth understanding of the response of weakly cemented mudstone under tri-axial compression loading state. The main outcomes obtained from this research indicated that: (1) the behavior of weakly cemented mudstone is closely sensitive to the confining pressure. As the confining pressure increases, both the peak strength and plastic deformation capacity of weakly cemented mudstone will be enhanced; (2) the main feature of weakly cemented mudstone after tests is its centrosymmetric "Z" shape, mainly attributed to the progressive separation of the particle element of mudstone; (3) the behavior of weakly cemented mudstone either in terms of the axial stress-axial strain or the failure mode is sensitive to the confining pressure. If the applied confining pressure is lower than 5 MPa, the micro-cracks are in the form of the single shear band, whereas the tested specimens will tend from brittle shear to plastic shear associated with the "X" shear when the confining pressure is higher than 5 MPa; and (4) The failure of weakly cemented mudstone is mainly attributed to the continuous expansion and penetration of internal microcracks under compression. The brittle failure mode of weakly cemented mudstone tends to ductile failure with the increase of confining pressure. The main contribution of this research is believed to be beneficial in deepening the understanding of the mechanics of weakly cemented mudstone under tri-axial compression and providing the meaningful reference to the practical application of water-preserved mining in the Ili mining area. [ABSTRACT FROM AUTHOR]

Coal production safety and protection of water resources in coal mines located under aquifers requires an in-depth analysis of key aquiclude strata (KAS), including their physical, mechanical, and seepage characteristics. Based on hydrogeological conditions of thickness and buried depth of coal seam, thickness and water abundance of the aquifer, KAS thickness, etc., the experimental comprehensive testing method of mechanical and permeability parameters of KAS in the Wugou Coal Mine, China, are proposed. This paper applies state-of-the-art X-ray diffraction (XRD), scanning electron microscopy (SEM), and mechanical test methods to study mineral composition, microstructure, mechanical properties, water absorption, and softening coefficient of KAS rock samples collected from the mine under study. The comprehensive analysis of the results obtained made it possible to clarify the particular water-inrush mechanism and stability control of KAS using the revealed stress-strain-permeability dependencies of composite KAS and non-Darcy seepage behavior of post-peak fractured KAS. The model of KAS damage status with different backfill effects is established and successfully applied to the case study. Findings of this study are considered instrumental in the KAS-based prevention of water-inrush hazards and more rational exploitation of coal resources. Image 1 • Mineral composition, microstructure, mechanical properties, water absorption, and softening coefficient of KAS are studied. • Water-inrush mechanism and stability control of composite KAS are revealed. • Findings of this study are considered instrumental in the KAS-based prevention of water-inrush hazards. [ABSTRACT FROM AUTHOR]

To better understand the physical and mechanical behavior of weakly cemented rock with different moisture contents for the success of water-preserved mining, this paper presents the systematic tri-axial compression tests on three typical rock samples (i.e., mudstone, sandstone, and sandy mudstone) sampled from Ili mining area, where the environmental requirements for water conservation are significantly strict. Both the influences of moisture content and confining pressure on the failure mode and the stress-strain behavior of weakly cemented rock have been discussed and compared with each other. Test results showed that: (1) compared to sandstone and sandy mudstone, both the peak stress and residual stress of the weakly cemented mudstone are much more sensitive to confining pressure and moisture content. In detail, the peak stress is very relevant to moisture content, whereas, the residual stress is more sensitive to the confining pressure, (2) with the increase of moisture content, both the yield and ductility of weakly cemented mudstone have been significantly enhanced. However, a similar experimental observation has been found for sandstone and sandy mudstone, and (3) the microstructure and the mineral component are believed to be the two main factors leading to the scatter in terms of the stress-strain behavior for different weakly cemented rocks. Experimental results and discussions presented in this paper can provide the guideline for further research on the application of water-preserved mining in other coal mines with a similar geological condition. [ABSTRACT FROM AUTHOR]