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Weathered bedrock aquifer is the main water-filled aquifer for coal mining in Jurassic coalfields in northern Shaanxi. The regional prediction of the water richness of weathered bedrock aquifer is the key to mine water control. Taking the central and western part of Hongliulin Minefield as the research area, based on the analysis of the factors affecting the water-richness of the weathered bedrock, the thickness of the weathered bedrock, the core removal rate, the degree of weathering, the combination of lithology, the top elevation of the weathered bedrock and the sand base ratio are selected to use as the discriminant indexes, 41 groups of effective weathered bedrock borehole pumping test data in the study area are used as training samples and verification samples with a 3∶1 random allocation method to construct a water-rich Bayes discriminant analysis model. This model is used to predict the water richness category of weathered bedrock that has not been drilled for pumping test in the central and western part of Hongliulin Minefield, and the water richness prediction diagram of weathered bedrock is obtained. The results show that the overall water-rich water in the western first panel of the study area is relatively strong, and the spatial distribution of strong water-rich area is uneven. Most areas of the north second panel and the south second panel have relatively weak water richness, and the extremely weak water rich areas are distributed in the southeast. By comparing with the actual production of the working face water inflow and the location of the water outlet point, the prediction result of the water-rich zone is consistent with the actual situation.

The pre-drainage of roof water in working face is one of the main means of water disaster prevention and control in coal mines in western China. Affected by the widely developed weakly cemented sand mudstone interactive stratum, the drainage drilling hole is easy to collapse and shrink, blocking the drainage channel, resulting in the rapid attenuation of the water inflow in a short time. The problem of hole collapse can be effectively solved by installing a steel screen tube with a total length longer than the depth of the unstable layer in the drilling. The attenuation rate of drilling water inflow and the total amount of drainage are used as the evaluation indexes of drainage effect. After installing the screen, the drainage efficiency of drilling for 30 days is increased by 49.3% compared with that before installation, and the drainage water in the drilling is increased by 10 times in the same time period.

Coal seam fire area is widely distributed in western coal area of China. When there is a strong hydraulic connection between the burned rock aquifer and other aquifers in the coal seam fire area, it will pose a serious threat to the safe mining of coal mine. Taking the 1-2 upper coal concealed burning area in the southeast corner of Ningtiaota Coal Mine as an example, based on various past hydro-geological data, the ancient topography before the deposition of Baode Formation was restored, and the stratum characteristics of the concealed fire area and the geological characteristics of the compensation channel drainage were analyzed. The factor analysis method is used to extract the characteristic factors reflecting the water abundance of burnt rock and weathered bedrock aquifer, and the comprehensive water-rich zone of burnt rock and weathered bedrock aquifer is obtained through GIS superposition method. The results show: the 1-2 upper coal seam burned from the early Cretaceous to the Pliocene, the development of ancient gullies provides favorable conditions for the formation of spontaneous combustion and burning metamorphic rocks in coal seams; the burnt rock aquifer and weathered bedrock aquifer in the concealed burning area are basically connected together to form a unified aquifer; the overburden rock combination relationship on 1-2 upper coal concealed burning area can be divided into three types, namely burnt rock-weathered bedrock combination, coal seam-burnt rock-weathered bedrock combination, coal seam-burnt rock-normal bedrock-weathered bedrock combination. Strong water abundance areas are mainly distributed in a small area in the north and west of the burning area, the medium water abundance areas are distributed in the burning area in a belt along the northwest-southeast direction; the eastern and northern areas of the concealed burning area are relatively weak in water abundance; the weak water abundance areas are distributed outside concealed burning area. Compared with the water inflow of underground water exploration and release boreholes, the evaluation of water abundance is in good agreement with the practice.

In the paper, N1212 working face was taken as the research object, the law and mechanism of surface cracks in shallow coal seam mining were studied by means of field investigation, dynamic monitoring and numerical simulation. The results show that the development degree of surface cracks in shallow coal seam mining is high, mainly “step” cracks, and the in-plane cracks are distributed at parallel intervals with an interval distance of 8-15 m. The cracks have two kinds of activity characteristics: “opening-closing” and “only opening and disconnecting”; the stress evolution and failure in the overlying strata extend forward in the form of “arch”, and the overlying rock fissures and surface cracks are connected with each other; the advanced generation and activity characteristics of surface cracks are closely related to surface movement and deformation, surface “tension-compression” deformation transformation and slope slip. The research results can provide a theoretical basis for the prevention and control of ground collapse in coal mining areas.

In order to study the development characteristics of water-conducting fracture zone in deep-buried gently inclined multi-coal seam mining, taking the overlapping mining area of 2-1 coal and 2-2 coal in Shicaocun Coal Mine as the research object, through the underground uphole water injection test and numerical simulation method, the overlying rock failure and the development characteristics of water-conducting fracture zone are studied. The results show that under the same geological and mining conditions, the development process of water-conducting fracture zone of overlying 2-1 coal with 1.8 m mining thickness and 2-2 coal mining thickness of 3.4 m can be divided into occurrence and slow increase stage, sudden increase stage and stable stage. However, the development rate of 2-2 coal water-conducting fracture zone is higher than that of 2-1 coal water-conducting fracture zone. Under the condition that the distance between 2-1 coal and 2-2 coal seam is 11 m, the height of compound water-conducting fracture zone produced by 2-2 coal mining is greater than that of 2-1 coal mining. After comprehensive analysis, it is determined that the development height of water diversion fracture zone in repeated goaf of multiple coal seams in Shicaocun Coal Mine is 49.6 m.

In order to study the surface movement and deformation law caused by the middle deep buried thick coal seam mining in northern Shaanxi Province, the first working face （112201 ｗｏｒｋｉｎｇ ｆａｃｅ） of Xiaobaodang Coal Mine which lies in the middle of the third phase planning area of Yushen Mining Area was taken as the research area. The surface movement and deformation characteristics, the movement deformation parameters and development laws of surface cracks caused by coal mining are obtained through the combination of observation station, GNSS observation station and theoretical analysis. The results show that: the maximum subsidence and the maximum subsidence coefficient were 3 840 mm and 0.66 respectively caused by mining of 112201 coal face. The duration of surface movement and deformation was about one and a half years. The start-up stage last 18 days, and the active stage last 110 days. Among the active stage, the surface movement and deformation are mainly concentrated in 43 days. The surface subsidence in the active stage was 91.4% of total subsidence value. The degree of development of surface crack induced by mining of 112201 coal face was weak. Relatively speaking, the development degree of surface cracks above the cut hole was greater than that above the trough, and the degree of the surface cracks above the goaf was weakest. The surface crack in the 112201 coal face was developed behind the mining position, and the width showed a “single peak” dynamic characteristic. There is coupling synchronization between the dynamic change characteristic and the velocity of surface subsidence.

Under the background of the ecological civilization era, rapidly obtaining coal mining information, timely assessing the ecological environmental impacts, and drafting different management and protection measures in advance to enhance the capacity of green mine construction have become the urgent technical problems to be solved at present. Simulating and analyzing mining subsidence is the foundation for a land reclamation plan. The Cellular Automata (CA) model provides a new tool for simulating the evolution of mining subsidence. This paper takes a mine in East China as a research area, analyses the methods and measures for developing a model of mining subsidence based on the theories of CA and mining technology, then discusses the results of simulation from different aspects. Through comparative analysis, it can be found that the predicted result is well consonant with the observation data. The CA model can simulate complex systems. The system of mining subsidence evolution CA is developed with the support of ArcGIS and Python, which can help to realize data management, visualization, and spatial analysis. The dynamic evolution of subsidence provides a basis for constructing a reclamation program. The research results show that the research methods and techniques adopted in this paper are feasible for the dynamic mining subsidence, and the work will continue to do in the future to help the construction of ecological civilization in mining areas.

Horizontal wells within the roof are an effective method to develop gas in broken and soft coal seams, and layer-penetrating fracturing is a key engineering method for the stimulating of horizontal wells within the roof of a coal seam. To understand the propagation law of fracture in the composite roof of coal seams, this study conducted research using numerical simulation and physical similarity simulation methods. Furthermore, engineering experiments were carried out at the Panxie coal mine in the Huainan Mining Area and the Luling coal mine in Huaibei Mining Area, to further validate this technology. The numerical simulation results indicated that fracture within the coal seam roof can propagate from the roof to the target coal seam, effectively fracturing the coal seam. Due to the coal seam's plasticity being greater than that of the roof mudstone, the coal seam forms a broader fracture than the roof. With the increase in pseudo roof mudstone thickness and being under constant fracturing displacement, the energy consumed by the pseudo roof mudstone during fracturing causes a decrease in pore pressure when fracture extends to the coal seam, resulting in a reduction in fracture width. Therefore, the pseudo roof mudstone is an adverse factor for the expansion of hydraulic fracturing. Physical similarity simulation results demonstrated that when horizontal boreholes were arranged within the siltstone of the coal seam roof, were under reasonable vertical distance and high flow rate fracturing via fluid injection conditions, and if the coal seam had a thin pseudo roof mudstone, the fracture could propagate through the direct roof-pseudo roof interface and the pseudo roof-coal seam interface, extending to the lower coal seam. The fracture form was curved and had irregular vertical fractures, indicating that hydraulic fracturing can achieve production enhancement and the transformation of soft and hard coal seams. However, when the coal seam had a thick pseudo roof mudstone, the mudstone posed strong resistance to hydraulic fracturing, making it difficult for the fracture to propagate to the lower coal seam. Therefore, the pseudo roof mudstone plays a detrimental role in hydraulic fracturing and the production enhancement of coal seams. The engineering verification conducted at Panxie coal mine and Luling coal mine showed that by utilizing a construction drainage rate of 7.5 cubic meters per minute at Panxie coal mine, the maximum fracture length reached 218.3 m, with a maximum fracture height of 36.8 m. The maximum daily gas production of a single well reached 1450 cubic meters per day, with a total gas extraction volume of 43.62 × 104 cubic meters across 671 days. At Luling coal mine, utilizing a construction drainage rate of 10 cubic meters per minute, the maximum fracture length reached 169.1 m, with a maximum fracture height of 20.5 m. The maximum daily gas production of a single well reached 10,775 cubic meters per day, with a total gas extraction volume of 590 × 104 cubic meters for 1090 days. This indicated that the fracture within the roof of coal seams can penetrate the composite roof of coal seams and extend to the interior of the coal seams, achieving the purpose of transforming fractured and low-permeability coal seams and providing an effective mode of gas extraction. [ABSTRACT FROM AUTHOR]

Models for recognizing the source of underground mine water is the basis for real-time monitoring of the water source in active underground mines. Real-time monitoring of the water source is of great significance for predicting water inrush and controlling flooding disasters. This study used the hydrochemistry data of the main aquifers of the Ningtiaota Coal Mine, Jiaozuo Coal Mine, Xieyi Coal Mine, and Huacheng Coal Mine. Through contrast experiments, the influence of dimension reduction processing of discriminant indexes and the selection of discriminant analysis methods in the recognition of the ability of the mine water source model were analyzed for different sample sizes for hydrochemistry data. The research shows that when the sample size is small, the dimension reduction processing using stepwise discriminant analysis and principal component analysis can significantly improve the model's ability to recognize the mine water source. The recognition accuracy of the model using the distance discriminant method is significantly lower than that of the other two methods, and the recognition ability of the Bayes model is slightly better than that of the Fisher model. When the sample size is large enough, the dimension reduction processing can no longer improve the recognition ability of the model, and all three methods have the same recognition ability. This study can provide an important reference for the establishment and optimization of mine water source recognition, and it is expected to be significant for the prediction and prevention of coal mine water inrush events. [ABSTRACT FROM AUTHOR]

The main aim of this study is to generate groundwater spring potential maps for the Ningtiaota area (China) using three statistical models namely statistical index (SI), index of entropy (IOE) and certainty factors (CF) models. Firstly, 66 spring locations were identified by field surveys, out of which, 46 (70%) spring locations were randomly selected for training the models and the rest 20 (30%) spring locations were used for validation. Secondly, 12 spring influencing factors, namely slope angle, slope aspect, altitude, profile curvature, plan curvature, sediment transport index, stream power index, topographic wetness index, distance to roads, distance to streams, lithology and normalized difference vegetation index (NDVI) were derived from the spatial database. Subsequently, using the mentioned factors and the three models, groundwater spring potential values were calculated and the results were plotted in ArcGIS 10.0. Finally, the area under the curve was used to validate groundwater spring potential maps. The results showed that the IOE model, with the highest success rate of 0.9126 and the highest prediction rate of 0.9051, showed the preferable performance in this study. The results of this study may be helpful for planners and engineers in groundwater resource management and other similar watersheds. [ABSTRACT FROM AUTHOR]