Evolution Characteristics of Pressure-Arch and Elastic Energy during Shallow Horizontal Coal Mining

To ensure safety mining during shallow horizontal coal mining based on the monitoring data of the roof weighting of a typical mining engineering in China, the load distribution characteristics of the roof in the mining field were analysed, and the mechanical model of the pressure-arch in the surrounding rock was established. Then the evolution characteristics of the pressure-arch and elastic energy were revealed during shallow coal mining by theoretical and numerical analyses. Results show that the continuous pressure-arch can form when the horizontal stress exceeds the vertical stress, and the elastic energy of the roof is released by the mining unloading effect. The caved zone of the overlying strata is formed below the inner boundary of the pressure-arch. The elastic energy is accumulated in the pressure-arch and the energy becomes the highest at the front arch foot. The sliding of the caved zone along the shear zone in the mining field can induce the strong roof weighting. The concentrated stress and the released energy during each mining stage increase with the working face advancing, and the height of the shear zone also increases. This study can provide a theoretical reference for similar mining engineering

Research on surface subsidence law in high-intensity mining of shallow buried with thick coal seam

Taking Daliuta Coal Mine in Western Shendong mining area as the engineering background, this paper selected typical shallow buried high-intensity mining panel 52307 to establish the observation station for surface movement. Combined RTK technology and 3D laser scanning technology for real-time monitoring, based on key layer theory and CISPM comprehensive surface subsidence prediction model software, the characteristics of surface movement and deformation, surface movement angular parameters and surface cracks in high-intensity mining of shallow buried was studied. The results showed that with the advance of the panel from the set-up room, the surface subsidence was small at the set-up room position and then increased suddenly and rapidly. Simultaneously, the subsidence curve became steep sharply. When the maximum subsidence value was reached, the subsidence velocity tended to slow down. The surface movement deformation was mainly concentrated in the middle of the panel, while the subsidence deformation around the panel and the influence range of surface movement was small. The surface movement angular parameters were quite larger in the Daliuta coal mine area, while the bedrock movement angle and boundary angle reached 87.7 ° and 84.1 ° respectively. The surface cracks caused by mining were in an overall “C” shape, mainly distributed in the middle of the panel. Then, As the working face continued to advance, the ground fissures continue to slowly extend, develop, and gradually close from the set-up room to the tailgate side, eventually forming a continuous surrounding "funnel" shape. Ground fissures always lagged behind the working face position and the lag distance of surface cracks increases linearly with the mining speed. According to the analysis of surface subsidence law and surface cracks development, it was concluded that under the condition of high-intensity mining of shallow buried with thick coal seam, due to the high mining intensity of the working face, fast advancing speed, single key layer structure and low occurrence horizon, the roof activity was intense and easy to slide and lose stability. As a result, it was appeared resulting in rapid convergence around the surface movement basin, serious damage in the middle, and intensive development of ground fissures

Analysis and application of backfill mining in thin coal seams for preventing building damage

As coal resources trapped under surface buildings impede the efficient mining of coal seams and constrain the sustainable development of coal mines, a super-high-water backfill mining technique for preventing building damage was adopted. According to the established model of equivalent mining height (EMH), the influence factors were obtained. Afterwards, a measurement to improve the backfill rate was analyzed based on the slurry fluidity. Meanwhile, the relationships between the backfill body compression and its influence factors were studied by numerical simulation. In this way, a more accurate EMH was obtained. To prove this trial practicable, the obtained EMH and the probability integral method were used to predict the surface movement and deformation of the C7401 panel. At the same time, a surface movement observation was set up to observe the mining influence on the surface ground and buildings. The comparison between the predicted and measured data indicated that they corresponded well with each other, the surface movement and deformation values were all controlled within grade I, which protected the surface buildings. Moreover, by applying the super-high-water backfill mining technique, not only building damage has been controlled within Grade I, but the impact on the ecological environment has been reduced also, such as surface subsidence, groundwater leakage and groundwater lowering, which is in harmony with the construction of green mines. The practical trial can provide a reference for mining under similar conditions and is vital for the sustainable development of the mining industry and economic growth

Research and application of maximum surface subsidence model under the condition of repeated mining in weakly cemented strata

The characteristics of surface subsidence under the condition of repeated mining in weakly cemented strata are of great significance to the safe and efficient mining and ecological restoration of coal resources in weakly cemented mining areas in western China. Theoretical analysis, similar simulation, numerical simulation and field monitoring are used to study the migration law of overlying strata and surface subsidence model under repeated mining conditions in weakly cemented strata, and the model is applied in engineering. The bulking characteristics of weakly cemented rock and the influence mechanism of repeated mining overburden strata movement on surface subsidence are discussed through theoretical analysis. The ‘maximum surface subsidence model under the condition of repeated mining in weakly cemented strata’ is established. There is a linear relationship between the bulking coefficient of weakly cemented rock, the mining thickness of lower coal and the maximum surface subsidence of weakly cemented strata. Through similar simulation and numerical simulation, the characteristics of repeated mining overburden and surface subsidence in weakly cemented strata are analyzed. The research results show that the development law of the separation height of the initial mining and repeated mining of the weakly cemented strata is basically the same, and both show a step-like rise. The surface subsidence curve of repeated mining is asymmetrically distributed, and the maximum subsidence value is biased towards the side of open cut. The maximum development height of overlying strata, the maximum surface subsidence value and the surface subsidence coefficient after initial mining and repeated mining are given. The established maximum surface subsidence model is used to predict the maximum surface subsidence value on site. The predicted value of the maximum surface subsidence model is similar to the measured value on site during the mining process of the working face, which verifies the rationality of the ' maximum surface subsidence model under the condition of repeated mining of weakly cemented strata '. At the same time, the predicted value of the maximum surface subsidence after the mining of the working face can provide a reference for the actual work on site

Effects of vegetation on the structure and diversity of soil bacterial communities in the Arctic tundra

The relatively simple vegetation of the Arctic tundra provides an ideal site in which to study the relationships between plants, bacterial communities and soil chemistry. Here, results of 16S rRNA gene sequencing of secondary Arctic brown soils collected from underneath colonies of Dryasoctopetala, Luzulaconfusa and Bistortavivipara in the Arctic tundra near Ny-Ålesund, Svalbard, Norway, reveal significant differences in bacterial communities related to soil environmental properties. Redundancy analysis shows that all measured geochemical factors were significant in structuring microbiomes, with strong correlations related to soil pH and organic matter contents. Vegetation is likely to affect the physical and chemical properties of the soil, which in turn affects the bacterial community and composition of the soil

Overlapping expression patterns and differential transcript levels of phosphate transporter genes in arbuscular mycorrhizal, Pi-fertilised and phytohormone-treated Medicago truncatula roots

A microarray carrying 5,648 probes of Medicago truncatula root-expressed genes was screened in order to identify those that are specifically regulated by the arbuscular mycorrhizal (AM) fungus Gigaspora rosea, by Pi fertilisation or by the phytohormones abscisic acid and jasmonic acid. Amongst the identified genes, 21% showed a common induction and 31% a common repression between roots fertilised with Pi or inoculated with the AM fungus G. rosea, while there was no obvious overlap in the expression patterns between mycorrhizal and phytohormone-treated roots. Expression patterns were further studied by comparing the results with published data obtained from roots colonised by the AM fungi Glomus mosseae and Glomus intraradices, but only very few genes were identified as being commonly regulated by all three AM fungi. Analysis of Pi concentrations in plants colonised by either of the three AM fungi revealed that this could be due to the higher Pi levels in plants inoculated by G. rosea compared with the other two fungi, explaining that numerous genes are commonly regulated by the interaction with G. rosea and by phosphate. Differential gene expression in roots inoculated with the three AM fungi was further studied by expression analyses of six genes from the phosphate transporter gene family in M. truncatula. While MtPT4 was induced by all three fungi, the other five genes showed different degrees of repression mirroring the functional differences in phosphate nutrition by G. rosea, G. mosseae and G. intraradices

Three-Failure Match

Based on the analysis and comparison of several major football match systems currently used, this paper summarizes the drawbacks of the current competition systems and puts forward a new match-making model - the three defeat match. By using the theory of probability Knowledge, the use of computer simulation method of the game and the original matchmaking system of quantitative analysis and comparison, the results show that the three defeat match focus group, knockout advantage, and can overcome these shortcomings system is a more reasonable Competition system

Top coal caving mining technique in thick coal seam beneath the earth dam

It is important to study the mining technology under structures for raising the coal resources recovery ratio. Based on the geological and mining conditions, the top coal caving harmonic mining technique in thick coal seam beneath the earth dam was put forward and studied. The 5 factors such as the panel mining direction, panel size, panel location, panel mining sequence and panel advance velocity were taken into account in this technique. The dam movement and deformation were predicted after the thick coal seam mining and the effects of mining on the dam were studied. By setting up the surveying stations on the dam, the movement and deformation of the dam were observed during mining. By taking some protective measures on the dam, the top coal caving mining technique in thick coal seam beneath the earth dam was carried out successfully. The study demonstrates that harmonic mining in thick coal seam is feasible under the dam. The safety of the earth dam after mining was ensured and the coal resources recovery ratio was improved. Keywords: Earth dam, Thick coal seam, Top coal caving mining, Harmonic mining, Mining damages and protectio