Strata movement and stress evolution when mining two overlapping panels affected by hard stratum

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scopus – master journals – JCR

ایمپکت فاکتور

۴٫۲۷۶ در سال ۲۰۲۰

شاخص H_index

۲۶ در سال ۲۰۲۱

شاخص SJR

۰٫۹۰۱ در سال ۲۰۲۰

شاخص Quartile (چارک)

Q1 در سال ۲۰۲۰

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Strata movement and stress evolution when mining two overlapping panels affected by hard stratum

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:
  1. Introduction

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 [11]; 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 [18].  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 [21].  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 [22].  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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