Strata movement and stress evolution when mining two overlapping panels affected by hard stratum
|نوع نگارش مقاله||
scopus – master journals – JCR
۴٫۲۷۶ در سال ۲۰۲۰
۲۶ در سال ۲۰۲۱
۰٫۹۰۱ در سال ۲۰۲۰
|شاخص Quartile (چارک)||
Q1 در سال ۲۰۲۰
خرید محصول توسط کلیه کارت های شتاب امکان پذیر است و بلافاصله پس از خرید، لینک دانلود محصول در اختیار شما قرار خواهد گرفت و هر گونه فروش در سایت های دیگر قابل پیگیری خواهد بود.
فهرست مطالب مقاله:
Mining causes stress redistribution and stratum movement. In this paper, a numerical model was built according to the geological conditions in the 12th coal mine in Pingdingshan city to study the strata movement and the evolution of stress when mining two overlapping longwall panels, named panels
#14 and #15. The strata close to the mined panel move directly towards the gob, while the strata that are farther away swing back and forth during the mining process. The directed movement and swinging can break the transverse boreholes for gas extraction; a surface borehole should not be within the range of directional movement. The stress evolution suggested that the mining of the lower panel #15 after the upper panel #14 would further increase the de-stressed range, while the stress concentration around the mined panel would be increased. Hard strata usually carry a greater stress than adjacent rocks and soft coal seams. The stress in a hard stratum increases greatly, and the stress decreases greatly in the coal seams below the hard stratum. This study supplies a reference for similar coal mines and is useful for determining the de-stressed range and transverse borehole arrangement for gas extraction.
|بخشی از متن مقاله:|
Deep coal seams usually bear a higher ground stress and a higher gas content than shallow coal seams, which increases the risk of gas outburst, and most coal seams deeper than 500 m are prone to dangerous gas release [1–۳]. To reduce the risk of explo- sion, the development of a safety coal seam as a measure of protec- tion is a method that is widely used all over the world. The redistribution of stresses and the movement of surrounding rocks during mining a protective coal seam is important for determining the pressure relief range and the location of the borehole to extract gas for pressure relief [4,5]. The recommended upper and lower pressure relief limits when mining a protective coal seam with a slope below 25 , according to Chinese law, are ۱۰۰ m and ۵۰ m, respectively, and coal mining enterprises are encouraged to study their own accurate parameters. However, in deep coal mines, methods for determining the pressure relief zone have been studied less extensively.Rock strata movement in the vertical direction is widely studied [6–۸]. The roof was divided into three zones in the vertical direc- tion, including the cave zone, the fractured zone, the original zone, and three zones in the horizontal direction, including the abutment stress concentration zone, pressure relief zone, and pressure recov- ery zone [9,10]. The boundaries of the zones are different in differ- ent rock strata, and currently there is no proper method to clearly identify the boundaries. Physical laboratory models were used to study the roof movement, and then identify the boundaries ; however, laboratory models are typically in 2D and cannot be used to represent the real conditions. The de-stressed range was also tested by a field experiment, which is an intuitive method for studying the evolution and distribution of pressure [12–۱۴]; how- ever, the testing points are usually insufficient and sometimes very difficult to determine. Roof movements caused by hard and thick sandstone were also investigated [15–۱۷], which was helpful for studying the abnormal characteristics of the gas flow and extrac- tion. The structural characteristics of key strata and strata behavior when mining a thick coal seam were also examined, and the results proved useful for determining the working resistance . Numer- ical modelling using elastic finite and boundary element methods was performed to analyze the stress redistribution, strata failure,
and water inflow enhancements that result from these coal mining operations [19,20].
In general, monitoring parameters is the most difficult aspect of laboratory or field experiments, and it is difficult to monitor stress or movement in the inner coal or rock. Numerical simulation is one of the most appropriate methods for underground studies and is widely used in underground engineering . Both physical and numerical models are simplified, because it is usually difficult to construct a large and sufficiently accurate model to represent the original geological conditions and stress field. In addition, there are usually several coal seams in one coal mine; for example, there are five valuable coal seams in the Pingdingshan coal field. Mining of several coal seams can lead to a complex stress evolution, which will greatly affect the de-stressed range . Mining of several coal seams will also cause complex strata movement in both the verti- cal and horizontal directions. Rock strata usually differ in hardness, which also leads to complication of the stress evolution and strata movement.
In this paper, we construct a numerical model according to the real geological conditions of the 12th coal mine in Pingdingshan and verify the model based on field results to study the stress evo- lution and strata movement when mining several overlapping longwall panels. The evolution of stress and the vertical stratum movement are helpful for determining the de-stressed range. Sur- face boreholes are used to extract gas to relieve pressure in the gob and to study the strata movement in the horizontal direction according to the location of the transverse boreholes. Because the hardness of the strata is quite different in the 12th coal mine, the stress evolution caused by strata hardness is also investigated in this paper.
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