TY - JOUR
T1 - Continuous Compaction and Permeability Evolution in Longwall Gob Materials
AU - Liu, Ang
AU - Liu, Shimin
AU - Wang, Gang
AU - Elsworth, Derek
N1 - Funding Information:
This study was sponsored by the Alpha Foundation for the Improvement of Mine Safety and Health, Inc. (ALPHA FOUNDATION). The views, opinions, and recommendations expressed herein are solely those of the authors and do not imply any endorsement by the ALPHA FOUNDATION, its Directors and staff. We also thank our partner mine, Tangkou coal mine, for support and for providing access to the mine for field work. The data used in this study can be downloaded from the Zenodo website ( https://zenodo.org/record/3929410 ).
Publisher Copyright:
© 2020, Springer-Verlag GmbH Austria, part of Springer Nature.
PY - 2020/12
Y1 - 2020/12
N2 - Understanding the evolution of gob compaction and related gas transport behavior is necessary for the planning and optimization of gas ventilation and control in longwall coal mines. In particular, the detachment of the undermined roof into the gob leaves a loosely compacted perimeter that skirts the longwall panel. This permeable gob perimeter in plan view forms as a result of shear separation from support provided by the solid ribs. This detachment and the resulting rotated and reduced stresses limit compaction, elevate permeability and exert significant control on gas flow during active longwall mining operations. We report gob compaction experiments on in-mine-collected fragmented rock and conduct mechanical compaction on stacked samples that are either uniformly coarsening upwards (case A) or are coarsening upwards, but capped by a segregated upper layer of coarse rock (case B). Observed compaction is linked to a capillary model representing porosity reduction and permeability evolution. As applied uniaxial stress increases from 0 to up to ~ 2000 kPa, the porosity decreases from 0.64 to 0.41(~ 36%) for the uniform stacked material (A) and but only from 0.66 to 0.51 (~ 23%) where the gob is topped with a layer of coarse “roof” rock simulants (B). Particle–particle self-adjustment dominates the compactive behavior at initial low stress and results in significant strain—followed by a linearly elastic region through the remainder of loading. The elastic regime is used to predict the permeability of the loosely compacted gob, considering the redistribution of stresses induced by shear collapse at the rib. Permeability evolution is scaled through the evolving compactive strains and particle size distribution of the fragmented rock, enabling results to be up-scaled to mine scale. These results provide a first rational method for analyzing the interactions between caved gob and the ventilation system towards mitigating gas concentrations and minimizing the hazard.
AB - Understanding the evolution of gob compaction and related gas transport behavior is necessary for the planning and optimization of gas ventilation and control in longwall coal mines. In particular, the detachment of the undermined roof into the gob leaves a loosely compacted perimeter that skirts the longwall panel. This permeable gob perimeter in plan view forms as a result of shear separation from support provided by the solid ribs. This detachment and the resulting rotated and reduced stresses limit compaction, elevate permeability and exert significant control on gas flow during active longwall mining operations. We report gob compaction experiments on in-mine-collected fragmented rock and conduct mechanical compaction on stacked samples that are either uniformly coarsening upwards (case A) or are coarsening upwards, but capped by a segregated upper layer of coarse rock (case B). Observed compaction is linked to a capillary model representing porosity reduction and permeability evolution. As applied uniaxial stress increases from 0 to up to ~ 2000 kPa, the porosity decreases from 0.64 to 0.41(~ 36%) for the uniform stacked material (A) and but only from 0.66 to 0.51 (~ 23%) where the gob is topped with a layer of coarse “roof” rock simulants (B). Particle–particle self-adjustment dominates the compactive behavior at initial low stress and results in significant strain—followed by a linearly elastic region through the remainder of loading. The elastic regime is used to predict the permeability of the loosely compacted gob, considering the redistribution of stresses induced by shear collapse at the rib. Permeability evolution is scaled through the evolving compactive strains and particle size distribution of the fragmented rock, enabling results to be up-scaled to mine scale. These results provide a first rational method for analyzing the interactions between caved gob and the ventilation system towards mitigating gas concentrations and minimizing the hazard.
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U2 - 10.1007/s00603-020-02222-z
DO - 10.1007/s00603-020-02222-z
M3 - Article
AN - SCOPUS:85089496427
SN - 0723-2632
VL - 53
SP - 5489
EP - 5510
JO - Rock Mechanics and Rock Engineering
JF - Rock Mechanics and Rock Engineering
IS - 12
ER -