Numerical Modeling Study of the Influence of Softcover on Strata and Support Behavior in a Bord and Pillar Depillaring Working

Abstract

This research focuses on the strata control issues in a Bord and Pillar depillaring working under the influence of dead load condition of voluminous and fragmented softcover of overburden dump material. It reports the modeling of a mine working through the FLAC 2D software under the Indian geo-mining conditions. The modeling results of an actual mine working under softcover were compared with that under the intact overburden condition to assess the influence of the soft overburden over the depillaring working. The modeling work involved progressive caving of the strata and the cyclic goaf filling following the model-simulated occurrence of main fall and periodic caving. Mohr-Coulomb Failure criteria along with a simplified strain-softening (MCSS) model was used to study the failure and caving mechanism. Salamon’s compaction model was used to simulate compaction and resultant stress recovery in the goaf material. Comparison of the model findings was done in terms of load on supports, abutment stress, and convergence, apart from the stress redistribution and failure mechanism. The load transfer mechanism of the soft overburden was also studied for an overall understanding of the strata behavior in such workings.

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Abbreviations

FA:

Face advance

HC:

Hardcover

IC:

Intact condition

IO:

Intact overburden

IP:

Intact parting

IR:

Immediate roof

LR:

Loading roof

MR:

Main roof

SC:

Softcover condition

SSC:

Settlement softcover condition

SIC:

Settlement intact condition

SR:

Settlement ratio

ν :

Poisson’s ratio

H :

Depth of cover

β :

Coefficient of thermal conductivity

E :

Elastic modulus

G :

Geothermal gradient

σ v :

Vertical stress

σ h :

Horizontal stress

σ c :

Compressive strength (MPa)

σ t :

Tensile strength (MPa)

c :

Cohesion (MPa)

ϕ :

The angle of internal friction (°)

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Acknowledgments

The authors are thankful to the Head, Department of Mining Engineering, IIT (BHU) for providing adequate laboratory and computational facilities. Further, they express gratitude to the M/s. BCCL for providing the site details for carrying out this scientific study.

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Correspondence to G. S. P. Singh.

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Highlights

• Numerical simulation results depicted that the main roof experienced a more dynamic loading effect as compared to the immediate roof in the soft overburden condition.

• Cumulative displacement of the yielded main roof and immediate roof strata increased after the periodic weighting in the depillaring working.

• Settlement at the surface is highest than the goaf material due to deformation of the fractured hardcover in the soft overburden conditions.

• Rib pillars faced shear failure in the horizontal direction due to the rotational and sliding tendency of the yielded block of the overlying immediate roof.

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Sahoo, S.K., Singh, G.S.P., Sharma, S.K. et al. Numerical Modeling Study of the Influence of Softcover on Strata and Support Behavior in a Bord and Pillar Depillaring Working. Mining, Metallurgy & Exploration 37, 1151–1168 (2020). https://doi.org/10.1007/s42461-020-00246-1

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Keywords

  • Softcover
  • Hardcover
  • Bord and Pillar
  • Depillaring
  • Caving
  • Deformation
  • Strata yielding