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Groundwater distribution influenced by mining activities is hard to be tracked due to the lack of accurate and real-time monitoring data. To address the groundwater dynamic change data under the mining conditions of open-pit coal mines, a three-dimensional automatic observation network of groundwater was constructed, and this observation network takes open-pit as the center, showing a radioactive distribution, based on hydrogeological conditions, and observes different aquifers. The data was analyzed by integrating hydrology, mining activity, and meteorological data. Analytic hierarchy process was adopted to reveal the underground disturbance influencing factors, and suggestions for groundwater protection were given. The results show that the dynamic variations of the groundwater with time can be divided into 3 types (precipitation affected, unaffected type, and mining affected types). The drainage operation during the open-pit mining triggered the drop of groundwater level, resulting in a cone of depression. The maximum drawdown of the central groundwater level was 60 m. And the disturbance mainly occurred in the mining area where the maximum groundwater disturbance radius was 8 km. Artificial drainage was the main disturbance factor of groundwater, and the range of groundwater level drop within the disturbance radius was closely related to the distance from the open-pit coal mine and the drainage volume. The closer the distance to the mines and the higher the drainage volume led to the deeper the groundwater level drop. This study shows the importance of the three-dimensional observation network of groundwater and provides a good reference for groundwater resources protection and ecological restoration in open-pit coal mines.

It is important to study the mechanism of water inrush on a seam floor by exploring the rules of permeability variations during rock deformation on the seam floor and in the course of fracturing as well as their responses to characteristics of the macromechanical environment such as mine ground pressure, engineering geology, and fluid mechanics. First, through the analysis of bearing pressure changes in the process of exploiting the working face, a mechanical model for the seam floor above the confined water is established. Based on the graphic data-processing software Mathcad, the computational process and methods for assessing the vertical, horizontal, and shear stresses are provided together with the corresponding variation curve of the rock stratum 5 m below the floor, covering the entire process from a position 120 m away from the working face to a position 280 m behind it. Second, the permeability coefficients of different lithologies are measured in the laboratory. For rock stratum 5 m below the floor, the corresponding external loading path is set up according to its actual stress. The actual dynamic stress environment of the rocks is simulated, and their permeability characteristics are studied. In addition, based on data fitting, the permeability coefficient variations in the mining process are determined for a rock stratum 5 m below the floor. Finally, in accordance with the permeability variation law of the floor of the working face, the seam floor is divided into six areas, namely, the compression and expansion zone, the bed separation and expansion zone, the pressure relief zone, the compression zone, the stable recovery zone, and the stability zone. Thus, the water-resisting performance of the floor can be expressed more objectively.

Based on well correlation, division of sedimentary facies and microfacies, core observation, and analysis of rock thin sections, the authors comparatively analyzed the sedimentation and diagenesis of the oolitic beaches in the Puguang and Yuanba areas of northeastern Sichuan Basin, and expounded their control on reservoirs. In the Puguang area the oolitic beach is thick and lateral migration distance is short, intervals overlaid one another, while in the Yuanba area the oolitic beach is thin and lateral migration distance is long. The two areas both experienced various types of diagenesis. There happened intense early dissolution and wide-spread dolomitization in the oolitic beach of the Puguang area, where type-I reservoirs of high porosity and permeability are developed. In the Yuanba area, strong compaction and pressure dissolution, and late burial cementation led to the development of type-III reservoirs of low porosity and permeability. The main factors that control the sedimentation and diagenesis are paleotopography and changes in sea level. Sedimentation controls the distribution and thickness of reservoir, and diagenesis determines the porosity formation and evolution and ultimately the reservoir quality. Key words: northeastern Sichuan, Feixianguan Formation, oolitic beach, sedimentation, diagenesis

The broken pattern of the overburden strata induced by mining has a non-ignorable effect on overlying strata movement, failure, and safety in mining production. To study the caving pattern of overlying strata and determine the calculation method of fracture pathway parameters due to roof caving induced by coal mining, the trapezoidal broken models were developed to explain and prevent water leakage, and even water inrush, during the mining process. By incorporating the variation of the volume expansion coefficient, a connection among the parameters of the fracture pathways and fracture angles, face width, and mining height could be established, which shows that the larger the degree of the fracture angle is, the smaller the value of the volume expansion coefficient and face width is with a relatively larger mining height. This relationship was also used to determine the eventual evolution configuration of the trapezoidal broken model. The presented approaches may help us to better understand the movement of overburden strata and provide an idea to help settle conflicts related to fracture space calculations induced by coal mining.

To identify the lithology of coal seam roof and explore the influence of these roofs on the enrichment of coalbed methane, low-frequency rock petrophysics experiments, seismic analyses and gas-bearing trend analyses were performed. The results show that the sound wave propagation speed in rock at seismic frequencies was lower than that at ultrasound frequencies. Additionally, the P-wave velocities of gritstone, fine sandstone, argillaceous siltstone and mudstone were 1,651 m/s, 2,840 m/s, 3,191 m/s and 4,214 m/s, respectively. The surface properties of the coal seam roofs were extracted through 3D seismic wave impedance inversion. The theoretical P-wave impedance was calculated after the tested P-wave velocity was determined. By matching the theoretical P-wave impedance of the four types of rocks with that of the coal seam roofs, we identified the lithology of the roofs. By analyzing known borehole data, we found that the identified lithology was consistent with that revealed by the data. By comparing and analyzing the coal seam roof lithology and the gas-bearing trends in the study area, we discovered that the coal seam roof lithology was related to the enrichment of coalbed methane. In the study area, areas with high gas contents mainly coincided with roof zones composed of mudstone and argillaceous siltstone, and those with low gas contents were mainly associated with fine sandstone roof areas. Thus, highly compact areas of coal seam roof are favorable for the formation and preservation of coalbed methane. [ABSTRACT FROM AUTHOR]

Groundwater is the main source of water in the grassland in eastern China, this region is one of the largest coal bases in China. It is of great significance to study the influence of opencast coal mine exploitation on the chemical characteristics of groundwater in grassland and thus to evaluate the suitability of irrigation water based on changes in the chemical characteristics of water. To study the background values of the chemical characteristics of groundwater and thus to assess the effects of high-intensity coal mine exploitation on groundwater, the water samples in this study were obtained from the mining site, as well as from private wells and rivers. It is found that the dominant hydrochemical types of the local surface water and groundwater are the Ca2+-Mg2+-HCO3– and Na+-Cl– types. The concentrations of Na+, HCO3– and SO42– are relatively high in these water samples, and nearly all of them exceed those in the WHO and GB 5749-2006 standards. Both the shallow aquifer water and surface water samples exhibit high salinity, low and moderate alkalinity, and low conductivity, which indicates that they can be used for irrigation. However, the quality of the deep groundwater samples is Permissible to Doubtful, and the coal seam aquifer water is not suitable for irrigation due to its high salinity, high alkalinity and high conductivity. To guarantee the safe usage of domestic and irrigation water, mine drainage is an important alternative to alleviate the local water usage contradiction. The post-processing drainage of coal seam aquifers should be fully taken into consideration. A groundwater monitoring network around the mining area, including urban areas, should be established and improved. The coal seam aquifer water source should be adequately avoided during future well drilling. [ABSTRACT FROM AUTHOR]

The exploitation of coal resources can lead to change of regional environment, and open-pit mining makes even more direct impact on vegetation, topsoil, surface water and underground water in grass area. Studying the change of hydrogeological condition caused by open-pit mining is beneficial for rational utilization of water resource in grass area and guaranteeing normal exploitation of open-pit mine. In this study, the Shengli 1 open-pit coal mine with typical hydrogeographical features, locating in typical meadow steppe area, was taken as researched area. Through collecting basic mine production data, such as annual output, drainage quantity, water inflow, the water inflow (including static- storage and recharge rate) of mine was predicted and calculated by horizontal catchment channel method, big well method and replenishment quantity method, respectively. This study investigates the hydrogeological condition changes of open-pit coal mine in grass area during production process. Results show that the static storage of hydrogeological unit exerts great impact to coal mine exploitation and production in early stage, while recharge rate exerts continuous influence to the whole mining process. As the quarternary loess in earth surface of steppe area is thick, and phreatic layer has a direct association with mining pit, the replenishment quantity method can achieve the most accurate calculation; the influence of open-pit mining to geohydrologic condition is mainly determined by aquifer hydraulic conductivity and mining depth. [ABSTRACT FROM AUTHOR]