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Abstract

Accurate understanding of the three-dimensional (3D) morphology of a complex goaf and its relative displacement in space is a precondition to further analyzing the stability of the cavity. In this study, to make an accurate stability analysis of the goaf, laser detection and numerical simulation are used to study the interior space form of goaf and the change characteristics of stress and displacement in goaf. The results of the study show that the BLSS-PE mining 3D laser system as a field detection tool can detect the morphology of the cavity more comprehensively and improve the accuracy of the detection data to a certain extent. Combined with the numerical simulation software analysis, it can be seen that the maximum principal stress in the 818-2# goaf increases after excavation. In addition, the maximum value appears in the top and bottom plates of the goaf, and the minimum stress remains nearly unchanged. The tensile stress appears in the upper and lower plates but is lower than the surrounding rock. The maximum horizontal and vertical displacements of the 818-2# goaf are small. The plastic zone appears in the surrounding rock of the goaf as the mining work progresses, but the area is small. It is concluded that the goaf is relatively stable overall. The research results may provide a strong reference for ground pressure management in mines and comprehensive control of goaves.
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Authors and Affiliations

Gangyou Sun
1
ORCID: ORCID
Yuandi Xia
2
ORCID: ORCID
Qinrong Kang
2
ORCID: ORCID
Weizhong Zhang
2
ORCID: ORCID
Qingzhen Hu
2
ORCID: ORCID
Wei Yuan
2
ORCID: ORCID

  1. The Fourth Research and Design Engineering Corporat ion, China
  2. School of Resources and Safety Engineering, Wuhan Institute of Technology, China
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Abstract

The impact of caulking of goafs after mining exploitation of a hard coal seam with caving is expressed as the change in value of a a exploitation coefficient which, as defined, is the quotient of the maximum reduction in the surface height of a complete or incomplete trough to the thickness of the exploited seam. The basis for determining the value of the exploitation coefficient was geological and mining data combined with the results of the measurement of subsidence on the surface – measuring line 1222-1301 – of the Ruda mine. There, mining was carried out between 2005 and 2019, with a transverse longwall system and the caulking of goafs. The research team used two methods to determine the impact of the caulking applied in the goafs on the value of the exploitation coefficient. In the first method the goafs are filled evenly along the whole longwall, and in the second method unevenly and on a quarterly basis. The determination of the values of the exploitation coefficients for selected measuring points was preceded by the determination of the parameters of the Knothe-Budryk theory, which was further developed by J. Białek. The obtained dependencies are linear and the values of the correlation coefficients fall between –0.684 and –0.702, which should be considered satisfactory in terms of experimental data. It is possible to reduce the value of the exploitation coefficient by caulking the goafs by about 18%, when filling the goafs to 0.26% of the height of the active longwall.
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Bibliography

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Authors and Affiliations

Andrzej Kowalski
1
ORCID: ORCID
Jan Białek
2
ORCID: ORCID
Tadeusz Rutkowski
3
ORCID: ORCID

  1. Central Mining Institute, 1 Gwarków Sq., 40-166 Katowice, Poland
  2. Silesian University of Technology, 2A Akademicka Str., 44-100 Gliwice, Poland
  3. PGG S.A. KWK Ruda, Ruda Śląska, Poland
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Abstract

The article presents a numerical model of a U-ventilated longwall, taking into account detailed elements such as arch yielding support, roof supports and shearer. What distinguishes it from previous models is the mapping of adjacent goafs. This model considers the current state of knowledge regarding spatial height distribution, porosity and permeability of goafs. Airflow calculations were carried out using the selected turbulence models to select appropriate numerical methods for the model. Obtained results show possibilities of conducting extensive numerical calculations for the flow problems in the mine environment, taking into account more complex descriptions and the interpretation of the calculation results carried out with simpler models.
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Bibliography

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Authors and Affiliations

Jakub Janus
1
ORCID: ORCID

  1. Strata Mechanics Research Institute, 27 Reymonta Str., 30-059 Kraków, Poland
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Abstract

The roof-caving step scale goaf behind the working face is sensitive to the region’s spontaneous combustion and gas concentration distribution, including many rock block cracks and holes. A severe deviation from the dynamics of fluids in porous media by representative element volume (REV), leading to the results of Computational Fluid Dynamics (CFD) simulation, has a significant error. A heterogeneous two-dimensional pore network model was established to simulate the goaf flow accurately. The network was first created using the simple cubic lattice in the OpenPNM package, and the spatial distribution of the “O-ring” bulking factor was mapped to the network. The bulking factor and Weibull distribution were combined to produce the size distribution of the pore and throat in the network. The constructed pore network model was performed with single-phase flow simulations. The study determined the pore structure parameters of the pore network through the goaf’s risked falling characteristics and described the flow field’s distribution characteristics in the goaf. The permeability coefficient increases as pore diameter, throat diameter, pore volume and throat volume increase and increases as throat length decreases. The correlation between throat volume and permeability coefficient is the highest, which indicates that the whole throat is the main control factor governing the air transport capacity in the goaf. These results may provide some guidelines for controlling thermodynamic disasters in the goaf.
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Authors and Affiliations

Ke Gao
1
ORCID: ORCID
Qiwen Li
1
ORCID: ORCID
Lianzeng Shi
1
ORCID: ORCID
Aobo Yang
1
ORCID: ORCID
Zhipeng Qi
1
ORCID: ORCID

  1. Liaoning Technical University, College of Safety Science and Engineering, Key Laboratory of Mine Thermodynamic Disasters and Control Of Ministry Of Education, China
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Abstract

Entries in steeply pitching seams have a more complex stress environment than those in flat seams. This study targets techniques for maintaining the surrounding rock mass stability of entries in steep seams through a case study of a steep-seam entry at a mine in southern China. An in-depth study of the deformation and instability mechanisms of the entry is conducted, employing field measurement, physical simulation experiment, numerical simulation, and theoretical analysis. The study results show that the surrounding rock mass of the entry is characterised by asymmetrical stress distribution, deformation, and failure. Specifically, 1) the entry deformation is characterised by a pattern of floor heaving and roof subsidence; 2) broken rock zones in the two entry walls are larger than those in the roof and floor, and the broken rock zone in the seam-floor side wall is larger than that in the seam-roof side wall; 3) rock bolts in the middle-bottom part of the seam-floor side wall of the entry are prone to failure due to tensile stress; and 4) rock bolts in the seam-roof side wall experience relatively even load and relatively small tensile stress. Through analysis, disturbances were found to occur in both temporal and spatial dimensions. Specifically, in the initial mining stage, the asymmetrical rock structure and stress distribution cause entry deformation and instability; during multiple-seam multiple-panel mining operations, a wedge-shaped rock mass and a quasi-arc cut rock stratum formed in the mining space may cause subsidence in the seam-floor side wall of the entry and inter-stratum transpression, deformation, and instability of the entry roof and floor. The principles for controlling the stability of the surrounding rock mass of the entry are proposed. In addition, an improved asymmetrical coupled support structure design for the entry is proposed to demonstrate the effective control of entry deformation.

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Authors and Affiliations

Panshi Xie
Yongping Wu
ORCID: ORCID

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