Multiscale Intelligent Inversion of Water-Conducting Fractured Zone in Coal Mine Based on Elastic Modulus Calibration Rate Response and Its Application: A Case Study of Ningdong Mining Area

Water-conducting fractured zone is the direct inducement of water inrush, water losing, and environmental deterioration in coal mines. How to predict the height of water-conducting fractured zone economically and accurately has always been the research difficulty of water-preserved mining. The paper selects the Meihuajing coal mine in Ningdong mining area as the engineering background. Firstly, transform the distribution law of the water-conducting fractured zone into a deterioration mechanism of coal-rock strength under the action of water-rock. Through laboratory tests, the water-rock coupling degradation law of rock mass under uniaxial action is revealed, and an intelligent statistical model of damage rate response under different water content is proposed. Secondly, based on the cross-scale elastic modulus calibration principle and the rate response intelligent statistical model proposed above, the borehole elastic modulus instrument is used to quantitatively characterize the strength characteristics of elastic modulus rate response law and field lithological parameters. Finally, based on the 18 samples of the water-conducting fractured zone, a height prediction model of a water-conducting fractured zone based on the measured value of elastic modulus is proposed by using the method of PSO-SVR. Taking R2 and RMSE as evaluation indexes, the error comparison between PSO-SVR and the empirical formula is carried out. Research indicates that, compared with the empirical formula, R2 of the PSO-SVR model increased by 18.3% and RMSE decreased by 92.7%. The predicted value of the PSO-SVR is consistent with the measured value, which significantly improves the prediction accuracy of the height of the water-conducting fractured zone. It provides a theoretical basis and technical support for the coordinated development of safe and efficient development of coal and ecological protection in Ningdong mining area.

Statistical analyses of groundwater chemistry in the Qingdong coalmine, northern Anhui province, China: implications for water–rock interaction and water source identification

Hydrochemistry of groundwater is important in coal mines because it can be used for understanding water–rock interaction and inrush water source identification. In this study, major ion concentrations of groundwater samples from the loose layer aquifer (LA), coal-bearing aquifer (CA) and Taiyuan Formation limestone aquifer (TA) in the Qingdong coal mine, northern Anhui province, China, have been analyzed by a series of statistical methods for identifying the source of chemical constituents in groundwater and the source of inrush water. The results indicate that the mean concentration of the major ions in the LA were ordered as follows: HCO3− > SO42− > Na+ + K+ > Cl− > Ca2+ > Mg2+ > CO32−, whereas average values of the CA in decreasing order are SO42−, Na+ + K+, HCO3−, Cl−, Ca2+, Mg2+ and CO32−, and the major ion concentrations of the TA have the following order: SO42− > Na+ + K+ > Ca2+ > HCO3− > Cl− > Mg2+ > CO32−, and most of the samples are Na-SO4 and Ca-SO4 types. TDS content in water increases with aquifer depth, whereas the pH values ranged from 7.1 to 8.9, indicating a weak alkaline environment. Two sources (weathering of silicate minerals and dissolution of evaporate minerals) have been identified by principal component analysis responsible for the chemical variations of the groundwater, and their contribution ratios have been quantified by Unmix model. Moreover, based on the Q-mode cluster and discriminant analyses, the samples with known sources have been identified correctly to be 95.7% and 97.6%, respectively, and the samples with unknown sources have been determined with high probability (78–100%).

Analisys of mud inrush water sources into underground working of the Sokolovskoe ore deposit

There is a serious threat of groundwater inrush from overlying sedimentary layers for underground mining. When ore is extracted using block caving method, the area of overburden collapse over ore zone disrupts the natural structure of high hydraulic-conductivity and low hydraulic-conductivity layers. This process creates conditions for the accumulation and transfer of groundwater to mine workings, which lead to accidents, up to disastrous proportions. The research aim is to determine the spatio-temporal distribution of mud inrushes, and to identify groundwater supply sources of inrushes to reduce the geotechnical risks of underground mining in Sokolovskaya mine. Research methods include localization, classification, and analysis of monitoring data, comparison of mud inrushes distribution with geostatistical parameters of the main aquifers.The majority of large-scale accidents caused by mud inrushes are confined to the central and northern area of caved rock zone. The most risky stage of the ore body extraction is the initial block at the lower extraction level. The sources of water supply for the majority of the mud inrushes are high water level areas of the Cretaceous aquifer to the north and west of the mine. Rational targeted drainage aimed at draining the identified areas of the aquifer is the best way to reduce the risk of accidents.

Research on Disaster-Control Method of Metro Station in Soft Fluid-Plastic Stratum

Soft and broken ground is a common geological condition for subway pit water damage. The complex hydrogeological environment is the main cause of frequent disasters. It relied on the inrush water project of the soft fluid-plastic stratum in the pit of the Shang Yuanmen station in Nanjing. And based on the geological data and the actual site of the project, the station was evaluated for hazards and analysis of major and difficult points. Combined with a variety of geophysical exploration methods, the source of water in the foundation pit and the key areas for pulp reinforcement was obtained. Based on field tests and indoor tests of grouting reinforcement, the parameters before and after grouting reinforcement were analyzed. The effect of material proportioning and grouting pressure on the parameters of stratum reinforcement was studied. It revealed the effect of the behavioral mechanism of material properties and grouting pressure on different mechanical indexes. It creatively proposes a localized controlled grouting process and uses COMSOL modeling to explain its reinforcement mechanism. In addition, foundation pits applied a full set of monitoring system. Finally, a complete set of comprehensive control methods were formed for water inrush in soft fluid-plastic stratum of complex urban strata. Then, the methods are implemented at the project site. Practice has proved that this method successfully seals the inrush water and reinforces foundation pits while ensuring the safety of foundation pits and surrounding construction pipelines. It is hoped that this method can be used as a reference for similar projects.

Damage Characteristics and Mechanism of a Strong Water Inrush Disaster at the Wangjialing Coal Mine, Shanxi Province, China

A serious groundwater inrush occurred at the Wangjialing coal mine on March 28, 2010. Great effort from all over the country was taken during the postaccident rescue. However, triggered by accumulated water in the upper abandoned tunnels and goafs of a nearby closed individually owned coal mine, it caused great damage, including 38 deaths and direct economic losses of over 49 million yuan. The inrush water was from the abandoned tunnels and goafs, which were filled subsequently by groundwater from the sandstone aquifer in the roof of the coal seam. The passage formed in the west roof of the heading face of the air return tunnel in the 20101 first mining face. Unidentified distribution and water-filled degree of the abandoned tunnels and goafs are critical bases for the accident. That important regulations for abundant groundwater exploration and release were not carried out thoroughly was another fatal cause leading to the accident. The poor awareness of water hazard controlling also contributed to the accident to a large extent.

Prediction of Mine Inrush Water Based on BP Neural Network Method

Based on predictions of the mine inflow of water and the complexity of influential factors, a method of BP neural network is put forward for mine inrush water prediction in this paper. We chose proper impact factors and establish non-linear artificial neural network prediction model after analyzed the impact factors of mine water inflow in Shandong Heiwang iron, and also made one prediction with normal mine water inflow during the iron mining operation. It turned out that the result can match with the actual prediction data, which make it possible to predict the mine water inflow with the prediction of Artificial Neural Network.

Heavy metals in groundwater from the Wolonghu coal mine, northern Anhui Province, China and their hydrological implications

Groundwater is important for either resource usage or safety of coal mining in north China. In this study, concentrations of eight kinds of heavy metals (Pb, Cd, Cu, Ni, Cr, Zn, Fe and Mn) in groundwater from three deep aquifers in the Wolonghu coal mine, northern Anhui Province, China have been analyzed for water quality assessment and water source identification. The results suggest that the groundwater have different concentrations of heavy metals among aquifers, which might be the results of different occurrence forms of heavy metals (e.g. Pb, Cd, Cu and Cr were adsorbed by iron hydroxides) and different kinds of water rock interactions (e.g. Mn and Zn originated from carbonate rocks). In comparison with the groundwater quality standard of China and WHO, most of them cannot be used for drinking directly but must be treated before drinking, especially the Pb, Cd and Fe contents. Moreover, hydraulic connection between aquifers has been identified by plots of factor scores and cluster analysis, which is similar to the results obtained by previous studies. Moreover, discriminant analysis demonstrated that heavy metals can be used for identification the source of inrush water in coal mines.